comparison of crt and lcd monitors quotation

CRT stands for Cathode Ray Tube and LCD stands for Liquid Crystal Display area unit the kinds of display devices wherever CRT is employed as standard display devices whereas LCD is more modern technology. These area unit primarily differentiated supported the fabric they’re made from and dealing mechanism, however, each area unit alleged to perform identical perform of providing a visible variety of electronic media. Here, the crucial operational distinction is that the CRT integrates the 2 processes lightweight generation and lightweight modulation and it’s additionally managed by one set of elements. Conversely, the LCD isolates the 2 processes kind one another that’s lightweight generation and modulation.

The obsolescence of CRT monitors requires replacing stimulators used for eliciting VEPs with new monitors. Currently, LCD monitors are the only suitable alternative, however other technologies, like OLED, may become a viable option [23]. So far, the ISCEV extended protocol for VEP methods of estimation of visual acuity recommends ensuring luminance artifacts caused by non-CRT stimulators [9], which can be achieved by reducing the stimulus contrast [23]. However, this may not be possible without falling below the minimum contrast values recommended for VEP [1, 23]. Since LCD stimulators have been shown to result in mostly a delay in the VEP responses [2,3,4, 23] but seem not to affect the size of the amplitudes [2], we expected no difference between the estimated visual acuity by using LCD or CRT monitors used as a stimulator for the sweep VEP.

The results of the first experiment show statistically significant effects of the monitor type on the time-to-peak after stimulus onset and the peak-to-trough amplitude (Table 1). The mean delay of the time-to-peak after stimulus onset between recordings obtained using the LCD and the CRT monitor was about 60 ms, which is quite high and possibly caused by the relatively old LCD monitor used. Accordingly, statistically significant effects on the time-to-peak after stimulus onset and the peak-to-trough amplitude were found for the monitor/contrast combination in the results of the second experiment (Table 4). Surprisingly, the mean delay of the time-to-peak after stimulus onset of the CRT monitors with high contrast was with up to 151 ms, longer (Table 5) than that of the LCD monitors (with low and high contrast), although one would expect modern monitors to have shorter or even no delays [24, 25]. Additionally, a statistically significant interaction between the spatial frequency and the monitor type was revealed in both experiments, causing an increased time delay for the intermediate spatial frequencies (1.4–10.3 cpd) with LCD stimulation (Fig. 2, top left) in the first experiment and an almost linear increase with the spatial frequencies in the second experiment (Fig. 2, bottom left). This may be explained by the semi-manual cursor placement, which is necessary because the amplitudes are less pronounced at frequencies below and above this frequency band. Another cause might be an input lag resulting from the time required by the monitor to prepare the image data to be displayed. This could be caused by, e.g., internal scaling for non-native resolutions, which may even be present when using the monitor’s native resolution. In the worst case, this leads to nonlinearities of the response timing of the LCD monitor when presenting patterns of low or high frequency [26, 27]. In doubt, the precise duration of the input lag should be measured using a photodiode attached to the display [28] and in case of being constant, the delay could then be subtracted from the respective time-to-peak values. Finally, the higher latencies may also be caused by the different software used for generating the stimuli: whereas in the first experiment, a custom-developed Java-based software was used, in the second experiment, the Python-based PsychoPy was employed. Nevertheless, these differences seem not to affect the estimated visual acuity. The mean peak-to-trough amplitude using the LCD monitor in the first experiment is reduced by about 0.9 µV with a confidence interval from − 1.6 to − 0.2 µV compared to the CRT stimulator, but increased by about 2.6 µV (confidence interval from 1.2 to 4.0 µV) when comparing the new LCD monitor with the CRT monitor (both with high contrast) in the second experiment (Table 5). However, these differences were, despite being statistically significant, within the expected standard deviation from about 0.5 to 7 µV of the P100 amplitude found in the literature [29,30,31] and therefore probably of no clinical relevance (Fig. 2, right). Interestingly, the results of Nagy et al. [2] suggest a similar reduction in the peak-to-trough amplitude when using an LC display for stimulation. In the first experiment, no statistically significant interaction between monitor type and spatial frequency on peak-to-trough amplitude was found but a tendency to smaller amplitudes at intermediate frequencies (Table 1), whereas in the second experiment, the effect of the interaction of stimulator and spatial frequency was statistically significant (Table 4). It has to be taken into account that the residuals of the models were heteroscedastic and therefore the statistical significance of the effects may be overestimated [32].

In the first experiment, the difference between the subjective visual acuity and that estimated by the second-order polynomial method, or by the modified Ricker function, was not statistically significant from a hypothetical assumed value of 0 logMAR (Table 2). Neither were the variances between CRT and LCD statistically different. Accordingly, the linear mixed-effects models revealed no statistically significant effects of neither the monitor type, the recording cycle, nor their interaction on the difference between subjective and estimated visual acuity for both estimation methods (Table 3).

In contrast in the second experiment, the differences between subjective visual acuity determined using FrACT and the visual acuities estimated using the modified Ricker function along with the conversion formula used in the first experiment were significantly different from the hypothesized difference of 0 logMAR for both, the new gaming LCD monitor and the old LCD monitor, at high and low contrast, but not for the CRT monitor. After using an individually adjusted conversion formula for each monitor/contrast combination, no statistically significant difference from the hypothesized difference of 0 logMAR was found (Table 7). However, one should keep in mind that using the results to calculate the conversion formula used to predict the results is circular reasoning. Nevertheless, it indicates, that using individual established conversion formulas calculated from a sufficiently large number of normative data will minimize the error between true visual acuity and estimated visual acuity.

Table 6 lists the signal-to-noise ratio calculated from the fitted Ricker model for the different combinations of monitors and contrasts. The highest SNR was found for the CRT monitor using high contrast. The LCDs showed lower SNR values. The on average higher amplitudes obtained using LCD monitors (Table 5) indicate that more noise is present when stimulating using LCDs. However, this effect could be caused by the different software used for the stimulus presentation and the lower number of sweeps recorded for averaging compared to the recordings using the CRT monitor. Nevertheless, none of the differences between the SNR values obtained from the different monitor types was statistically significant (Table 6), which corresponds to the findings of Fox et al. [28].

We want to point out the limitations of the current study: We included only healthy participants, so the possible effects of LCD stimulators on patients with reduced visual acuity remain unclear and should be further investigated, especially since we found a statistically significant, albeit not clinically relevant, effect of the monitor/contrast combination on peak-to-trough amplitude and time-to-peak after stimulus onset in the second experiment (Tables 4, 5). Further limitations are that the participants were not stratified by age and that the subjective visual acuity in the first experiment was determined using an eye chart projector, in contrast to the second experiment, where FrACT was used, limiting the accuracy of the estimated value. Finally, this study compared only three specific monitors; therefore, the results are not universally valid.

In conclusion, based on the results of this study, LCD monitors may substitute CRT monitors for presenting the stimuli for the sweep VEP to objectively estimate visual acuity. Newer LCD screens, especially with low response times in the range of 1–2 ms, therefore, allow for a reduction in luminance artifacts at required contrast levels [23], albeit the luminance artifact may not have a large effect on the recorded signals [28]. New technologies like OLED displays [23] may even be better suited, since one the one hand, the onset will be the same for the whole pattern, and on the other hand, LCDs and OLEDs provide a constant luminance level during stimulation, whereas CRTs need a constants pulses to keep the phosphor lit up, causing fast local luminance flashes all the time [28]. Therefore, in contrast to CRTs, LCD and OLED stimulators, e.g., may allow for recording true offset responses [33]. However, caution should be taken when leveraging modern displays for stimulation, since their in-built electronics perform all kinds of sophisticated image-enhancing procedures including color-correction, brightness boosting, contrast enhancement by real-time adjustments of the colors or the backlight, or eyestrain-reducing blue light filtering, with the aim to improve the users’ experience, or to increase the monitors lifetime. This applies in particular to consumer electronics like TVs. Gaming monitors, in addition, use special acceleration drivers, which shut down the backlight, insert black frames (Black Frame Insertion, BFI), or employ variable refresh rates (e.g., Nvidia G-SYNC or AMD FreeSync) to clean the retained image from the eye. Therefore, one should disable any image processing or enhancing functionality in the monitor settings, before using the monitor as stimulator for electrophysiological experiments. Finally, it is advisable to perform a calibration with healthy volunteers using best-corrected and artificially reduced visual acuity and to collect normative data for the employed setup, as always recommended by ISCEV [34], in order to establish an individual conversion formula between the sweep VEP outcome and the estimated visual acuity.

If you are looking for a new display, you should consider the differences between CRT and LCD monitors. Choose the type of monitor that best serves your specific needs, the typical applications you use, and your budget.

Require less power - Power consumption varies greatly with different technologies. CRT displays are somewhat power-hungry, at about 100 watts for a typical 19-inch display. The average is about 45 watts for a 19-inch LCD display. LCDs also produce less heat.

Smaller and weigh less - An LCD monitor is significantly thinner and lighter than a CRT monitor, typically weighing less than half as much. In addition, you can mount an LCD on an arm or a wall, which also takes up less desktop space.

More adjustable - LCD displays are much more adjustable than CRT displays. With LCDs, you can adjust the tilt, height, swivel, and orientation from horizontal to vertical mode. As noted previously, you can also mount them on the wall or on an arm.

Less eye strain - Because LCD displays turn each pixel off individually, they do not produce a flicker like CRT displays do. In addition, LCD displays do a better job of displaying text compared with CRT displays.

Better color representation - CRT displays have historically represented colors and different gradations of color more accurately than LCD displays. However, LCD displays are gaining ground in this area, especially with higher-end models that include color-calibration technology.

More responsive - Historically, CRT monitors have had fewer problems with ghosting and blurring because they redrew the screen image faster than LCD monitors. Again, LCD manufacturers are improving on this with displays that have faster response times than they did in the past.

Multiple resolutions - If you need to change your display"s resolution for different applications, you are better off with a CRT monitor because LCD monitors don"t handle multiple resolutions as well.

So now that you know about LCD and CRT monitors, let"s talk about how you can use two monitors at once. They say, "Two heads are better than one." Maybe the same is true of monitors!

First, we will provide a brief technical overview of functional principles as they relate to visual stimulus presentation. Detailed descriptions and parameter measurements are already available from the existing literature; however, our intention here is to equip readers with limited technical expertise with the necessary knowledge to set up computer experiments with LCD monitors. Thus, we keep our explanations relatively short and simplified.

LCD monitors work differently: Each pixel consists of liquid crystal threads that can be twisted or arranged in parallel by an electrical current applied to them. This leads to a polarization effect that either allows or prevents light passing through. A white light source located behind this crystal array uniformly and constantly illuminates the array. To display a black pixel, the crystal threads are twisted by 90° such that no light will pass through. A white pixel is achieved by aligning the crystals such that maximum light is allowed to pass through, until a different, non-white color needs to be displayed (see the lower panel of Fig. 1 for an LCD pixel’s brightness over time). This is a static process, not a pulsed one as in CRTs.

In theory, the difference in presentation methods, namely a strobing versus a static image, should be of no consequence if the light energy that falls onto the retina remains the same over the time period of one single frame. As the Talbot-Plateau law states2 is equally well detectable as a light flash presented for 60 ms at 40 cd/m2. This suggests that temporal integration can be easily described by energy summation”. Thus, in principle, LCD and CRT monitors should be able to yield comparable results.

However, due to the differences in technology, the visual signals produced by the two display types have different shapes (i.e., a different light energy-over-time-curve; see Fig. 1). Moreover, default luminance as well as visual-signal response times (in addition to other parameters, see below) differ between most CRT and LCD monitors

Table 1 reports the parameters we considered in setting up the CRT and LCD monitors. Certainly, most of them are commonly considered when setting up a computer experiment; nevertheless we deemed it important to mention them here explicitly, as their neglect might have unintended consequences. We used a 17” Fujitsu Siemens Scenicview P796-2 CRT color monitor previously used in several published studies including studies with masked presentation conditions

We tested various monitor user settings, refresh rates, resolutions and luminance settings (see materials available at https://osf.io/g842s/) with regard to the emitted light energy–over-time-curve and therefore response characteristics (i.e., onset and offset of full screen and centrally presented stimuli). Measurements were conducted with a photodiode setup, using both an oscilloscope (model “Agilent MSOX 3012 A”) and a self-developed microcontroller setup as measurement devices. Stimuli were black and white squares.

Our measurements revealed several interesting characteristics: First, luminance of the LCD monitor at default setting (i.e., maximum brightness) exceeded the CRT luminance at a ratio of 3.25:1. However, comparable average luminance can be (and was) achieved by downregulating the LCD monitor (the older CRT technology emits less energy even at maximum settings, see Table 2), without participants perceiving it as unnaturally dark. If one plans to upgrade from CRT to LCD monitors in an experimental laboratory, we therefore recommend measuring the CRT monitors’ brightness levels and matching them in the new LCD monitors’ user setup, if comparability with the old setup is needed. This will minimize hardware-dependent variability, thus contributing to better replicability. Please note that a brightness adaption is not a necessary precondition when employing LCD monitors; researchers should simply be aware that the brightness level can have an influence onto the resulting effects, especially in time-critical experiments with short and/or masked presentation. Thus, we recommend the adaptation for time-critical experiments in which researchers orient on existing empirical evidence gathered with CRT monitors. Furthermore, gray-to-gray response times varied slightly depending on the employed brightness levels2), so we suggest that researchers can rely on this more efficient method as an approximation.

For the empirical comparison of human performance with CRT and LCD monitors, we relied on these results and set the monitor settings accordingly (see Method section below).

Participants were administered a masked number priming task and a subsequent forced-choice prime discrimination task using both a CRT and an LCD monitor. In this well-established paradigm

Of central interest was the question whether both monitors would yield comparable masked priming effects. Monitors were set according to the parameters described in the previous section (see also Method section below). In order to obtain conclusive evidence, we decided for sequential hypothesis testing using Bayes factorshttps://osf.io/g842s/.

Responsible for performing installations and repairs (motors, starters, fuses, electrical power to machine etc.) for industrial equipment and machines in order to support the achievement of Nelson-Miller’s business goals and objectives:

• Perform highly diversified duties to install and maintain electrical apparatus on production machines and any other facility equipment (Screen Print, Punch Press, Steel Rule Die, Automated Machines, Turret, Laser Cutting Machines, etc.).

• Provide electrical emergency/unscheduled diagnostics, repairs of production equipment during production and performs scheduled electrical maintenance repairs of production equipment during machine service.

"Between 0.0001 and 0.00001 nits" "Sony claims an OLED contrast range of 1,000,000:1. When I asked how the contrast could be so high I was told that the surface is SO black the contrast is almost infinite. If the number representing the dark end of the contrast scale is nearly zero then dividing that number into the brightest value results in a very, very high contrast ratio."

Does not normally occur at 100% brightness level. At levels below 100% flicker often occurs with frequencies between 60 and 255 Hz, since often pulse-width modulation is used to dim OLED screens.

No native resolution. Currently, the only display technology capable of multi-syncing (displaying different resolutions and refresh rates without the need for scaling).Display lag is extremely low due to its nature, which does not have the ability to store image data before output, unlike LCDs, plasma displays and OLED displays.

We often get asked, “should I replace my old CRT with a new LCD? What is the difference?” There are several factors to consider including price, resolution, energy savings and disposal. Listed below are some of the top reasons why the LCD may be a better choice.Size and Weight: The color LCD is thinner and much lighter. It is much easier to install into tight areas. The CRT can weigh up to 50 pounds and needs additional bracing and heavier supports.

Price: At first glance, the CRT wins here. It is older technology and the price is cheaper. However you give up all the features mentioned in this list. Also disposal costs and higher energy costs may negate any price savings.

Power: Energy savings on the LCD can make a big difference in companies having multiple units in production. Savings can be as much as 1/3 over the older CRT.

Summary: Based on price alone, you may choose to stay with the CRT. However, you must consider the energy cost savings to operate an LCD vs. CRT, plus the added cost of disposal for CRTs. In many instances, the CRT may actually cost more in the long run. With its large, high resolution screen and compact housing for easy installation, the LCD offers many advantages over the older CRT technology.

There are two primary types of computer monitors in use today: LCD monitors and CRT monitors. Nearly every modern desktop computer is attached to an LCD monitor. This page compares the pros and cons of both the CRT type displays and LCD or flat-panel type displays. You"ll quickly discover that the LCD or flat-panel displays pretty much sell themselves and why they are the superior display used today.

LCD monitors are much thinner than CRT monitors, being only a few inches in thickness (some can be nearly 1" thick). They can fit into smaller, tighter spaces, whereas a CRT monitor can"t in most cases.

Although a CRT can have display issues, there is no such thing as a dead pixel on a CRT monitor. Many issues can also be fixed by degaussing the monitor.

LCD monitors have a slightly bigger viewable area than a CRT monitor. A 19" LCD monitor has a diagonal screen size of 19" and a 19" CRT monitor has a diagonal screens size of about 18".

No native resolution. Currently, the only display technology capable of multi-syncing (displaying different resolutions and refresh rates without the need for scaling). Display lag is extremely low due to its nature, which does not have the ability to store image data before output, unlike LCDs, plasma displays and OLED displays.

"I"ve been staring at my computer for hours" is an often heard refrain, normally uttered in a zombie-like state. Of course, it"s actually the monitor you are "staring" at, but for many of us the monitor is the computer. The right monitor should offer good image quality and a sizable viewing area while comfortably fitting your desktop space. Picking a monitor which combines these traits means you"ll want to learn the basics about monitor features and technology. After a quick lesson, it"ll be easy to choose a monitor that makes everything from spreadsheets to space aliens eye-popping and easy to read.

The most prevalent type of monitor today is the cathode ray tube (CRT). Despite its rather sci-fi sounding name, a CRT is the same as the picture tube inside your TV. They work by firing beams of electrons at phosphor dots on the inside of a glass tube. The phosphors in a CRT are chemicals that emit red, green or blue light when hit by electrons. These monitors are capable of multiple resolutions, give the best look to full-motion video and provide better control over colour calibration for graphic artists.

On the down side, they hog a lot of room and weigh more than several sacks of potatoes. You can get more compact CRTs called short-depth or short-neck monitors which are a couple of inches shallower than regular CRTs. Unless space is a primary consideration, most people buy a CRT display because they offer good performance at an affordable price.

In the opposing corner are flat panel displays or LCDs (liquid crystal displays) commonly used in laptops and fast becoming popular as desktop monitors. Their major selling points are a slim profile and light weight. A CRT can be deeper than it is wide, whereas a LCD with a base is only about a handspan deep. No heavy lifting required with a LCD; they weigh less than half the average CRT. LCDs require half the power of CRTs and emit much less electromagnetic radiation which can interfere with other electronic devices.

In the screen of a LCD monitor, each pixel is produced by a tiny cell which contains a thin layer of liquid crystals. These rod-shaped molecules bend light in response to an electric current. It"s the same display technology that resides in your digital watch but more sophisticated.

LCDs tend to be clearer than CRTs which can suffer from convergence or focus difficulties. Their improved clarity means that even small LCDs can display higher resolutions than the corresponding sized CRT. They also make small text easier to read. Unlike CRTs, LCD monitors have only one optimal resolution. At lower resolutions, the screen is redrawn as a smaller area or all the pixels in the image are blown-up to fill the screen. The latter solution can make images look jagged and blocky so be sure the resolution of the LCD is the resolution you want to use.

Regardless of what type of monitor you"re considering, size is a priority. A bigger monitor offers easier to read text, better graphics and the ability to have more and larger windows open on your desktop. All monitor sizes are measured diagonally across the screen, but that number isn"t the true viewable area. The plastic frame around the monitor hides a certain amount of the screen so there is a difference between the quoted size and the actual viewable area. A monitor"s viewable area should be within an inch or so of the quoted size.

The standard monitor size used to be 15 inches, but 17-19 inch monitors have become the norm as prices have decreased. You can get a 17 inch CRT starting at $300. An adequate 19 inch CRT can be had for $400 but better quality will cost more. If you need a large screen for group presentations, a 29 inch monitor will cost a few thousand dollars. You can get a 29 inch PC/TV hybrid monitor for about $1000, but these monitors have low resolutions and are unable to produce high-quality images.

A LCD is about double the cost of a CRT with a comparable viewing area. The minimum size you should consider for a LCD is 15 inches with prices starting at $600. Larger LCDs go up in price from there with an 18 inch monitor costing around $3000. Buying a flat panel display will definitely leave your wallet flatter too.

A factor for both CRTs and LCDs is resolution. The number of pixels horizontally and vertically defines a monitor"s resolution in pixels or dots per inch (ppi or dpi). The greater the resolution, the more information or image you"ll be able to view at once. The average user will find a resolution of 1024x768 more than sufficient for everyday work. You can achieve this resolution on CRT monitors 17 inches and larger or LCDs 15 inches and larger. Keep in mind that CRTs can display multiple resolutions, but LCDs are optimized at only one resolution.

Monitors can come with a variety of extras. Some have built-in speakers or jacks for microphones and headphones. Other monitors have dual inputs so you can connect two computers to the same monitor. With the advent of USB (Universal Serial Bus), some monitors have USB hubs at the back, allowing you to connect more peripherals. You can also get accessories like anti-glare filters and specialized mounting stands that help minimize glare and provide a comfortable working position.

To keep your utility bill down, you should look for a monitor that is Energy Star compliant. Energy Star is a program developed by the US Environmental Protection Agency (EPA) to make energy-saving office equipment like computers and monitors. An Energy Star monitor automatically goes to sleep or powers down after a period of inactivity. This feature can save 60-80% of power during idle times. All you have to do to wake up the monitor is touch the keyboard or mouse.

The majority of monitors are certified as "low emission" since they meet standards like MPR II or TCO. These guidelines were developed in Sweden (the acronyms are Swedish too) by a number of organizations to set limits for electric and magnetic field emissions. The newer TCO standards are the strictest. So if you"re concerned about emissions look for MPR II or TCO certification, not just the words "low emission."

If you"ve decided to get a new CRT then it should have a sufficiently high refresh rate. This refers to how often the screen is redrawn per second. With low refresh rates you can get screen flicker and eye strain. Aim for a rate of 75 Hz for a monitor up to 17 inches in size and 85 Hz for any larger monitor. LCDs are basically flicker free so refresh rates aren"t important.

Another consideration for CRTs is dot pitch. This is the distance in millimeters between phosphors of the same colour. The smaller the dot pitch, the sharper the image. Opt for a dot pitch of 0.26 mm or smaller. You can measure dot pitch both horizontally and vertically, but monitor specs usually quote horizontal dot pitch. Occasionally, the dot pitch is measured diagonally. By multiplying diagonal dot pitch by 0.866, you can calculate horizontal dot pitch.

One of the main disadvantages of LCDs when compared to CRTs is their limited viewing angle. When viewing a LCD straight on it looks fine. But the screen will appear washed-out if you move your head over to the side and look at it from an extreme angle. Low-end LCDs can have viewing angles of only 100 degrees which won"t give everyone crowded round your desk a clear view. For a standard 15 inch LCD try to get a 140 degree viewing angle. Up that by 20-40 degrees when shopping for an 18 inch LCD.

The brightness of LCD monitors is another important factor. LCD monitors have several backlights that provide illumination. Brightness is measured in units called nits. The majority of LCDs produce 150-200 nits which is fine for most users. The backlights in a LCD are good for 10 to 50 thousand hours of operation.

Since they"re fairly fragile and more likely to break, backlights usually come with only a one year warranty. This warranty is separate from the one for the screen so you might want to extend the backlight warranty to match the duration of your screen warranty.

LCDs can provide a range of options for positioning a display. The common way to view a screen is landscape mode (longer than wide). Some LCDs let you pivot the screen 90 degrees so you can view it in portrait mode (taller than wide) which is great if you"re growing tired of scrolling so often. You should also check out whether the screen can both tilt and swivel. Easy adjustment is important if you"ll be doing presentations. You can even mount some LCDs on the wall like a picture.

If space and aesthetics are important to you, then a flat panel is the way to go. Compared to CRT displays they use very little power, emit less heat and radiation, take up a smaller amount of space and are easy on the eyes.

If space is not an issue, it"s probably better to get a good quality 19" CRT monitor than an entry-level 15" flat panel. As well, if you use your computer a lot for graphics and games, a CRT offers a sharper and more detailed display.

The best thing you can do is spend some time at an electronics store and put a flat panel through its paces. Open up Word and start typing, read the text and view images and video if possible.

If you"re an apple enthusiast, you"re in luck. The Apple flat panels are top of the line and display incredibly clear images, text and video. The price is steep but the results are worth it.

Vision science experiments have historically depended upon cathode-ray tube (CRT) monitors to present stimuli with high spatial and temporal acuity. However, due to competition from plasma screens and liquid crystal displays (LCDs), CRT production was reduced or ceased by most manufacturers throughout the mid-2000s, meaning that many vision scientists now largely depend upon old and increasingly unreliable CRT monitors. Although CRTs are far from perfect numerous studies have described their superior performance relative to LCDs (e.g., Elze et al., 2007; Elze and Tanner, 2011, 2012). In recent years, however, high-quality LCDs targeting gamers have become commercially available. Further, two specialized companies now produce LCDs that aim specifically to meet the needs of vision researchers (“ViewPixx,” VPixx Technologies Inc., Canada, and “Display++,” Cambridge Research Systems, UK). Here, we compare the spatial and temporal luminance characteristics of these high-end research LCD monitors with more readily available gaming LCDs and CRTs.

Although CRTs are often considered the gold-standard monitor for use in vision research, they still have a number of limiting features (García-Pérez and Peli, 2001). CRTs generate an image by focussing an electron beam onto a phosphor layer, which emits visible light when struck by an electron. Color monitors use three phosphor layers, which each emit light with a different wavelength. The electron beam is rapidly “raster” scanned in rows, from the top-left to the bottom-right of the monitor, meaning that the entire image cannot be updated simultaneously. The decay rate of the phosphor"s fluorescence, in combination with the rapid electron scanning, means that CRT monitors are unable to deliver continuous luminance patterns and the emitted light flickers at the frame rate used to generate images. This flicker is typically at 60–120 Hz, and while typically perceptually invisible, can strongly affect neural responses to visual stimuli (Wollman and Palmer, 1995; Krolak-Salmon et al., 2003; Williams et al., 2004). The relatively poor spatial independence in adjacent pixels in CRT monitors is also a major drawback, introducing artifacts to stimuli with high spatial frequency (Cowan, 1995; Bach et al., 1997; Pelli, 1997a; Krantz, 2000). Some older CRTs exhibit problems with focus of the electron beam and unreliable reproduction of low luminances.

LCDs use liquid crystals as voltage-controlled filters to control light emission. Light from a source at the back of the monitor (e.g., a light emitting diode or cold cathode fluorescent lamp) passes through three consecutive filtering layers: a polarizing filter; a layer of liquid crystals; and finally a second polarizing filter oriented orthogonal to the first. Light intensity is determined by the level of polarization change introduced by the liquid crystal layer: if no voltage is applied to the liquid crystals, they align such that the liquid crystal layer introduces a 90° change in polarization angle, and maximum light intensity will be achieved. As the voltage applied to the liquid crystals increases, they progressively change alignment, blocking more light. Unlike CRTs, each pixel in an LCD monitor is an independent filter element, allowing independent adjustment of the luminance of each pixel (Krantz, 2000; Wang and Nikolic, 2011). Nevertheless, LCD displays do exhibit two key temporal problems: first, temporal artifacts may arise depending on whether the light source is continuously on, flashed briefly once per frame, or subjected to pulse width modulation (PWM) to control brightness (Elze et al., 2007; Liang and Badano, 2007; Elze and Tanner, 2011, 2012). Second, significant temporal constraints occur due to the sluggish nature of switching in liquid crystals. This latency is undesirable in experiments with rapidly changing or fast moving stimuli, as the slow dynamics causes problems such as motion blur (Hong et al., 2005; Pan et al., 2005; Someya and Sugiura, 2007; Becker, 2008; Feng et al., 2008; Watson, 2010). Furthermore, the measured light intensity can dramatically change as the visual angle of the observer varies.

The demands of vision scientists using moving or reverse correlation stimuli, which are updated rapidly, are similar to the demands of many computer games. These games have driven the development of LCD monitors with high spatial resolution, high temporal refresh rates (100–120 Hz) and precise control over when and where light is emitted from the monitor on each frame refresh. Recent advancements in display technology have also facilitated the development of professional LCD monitors that are intended to meet the spatial and temporal requirements of vision science experiments. Given the constraints of CRT monitors, and the rapidly expanding market for LCD monitors, we examined whether any LCD monitors are suitable replacements for CRTs in the laboratory. In this study, we characterized and compared the spatial and temporal properties of a CRT monitor, two LCD monitors made specifically for vision sciences, two high quality gaming LCDs, and a consumer-grade LCD.

Our spatial tests demonstrate that most LCDs exhibit a dramatic decline in luminance toward their periphery, with effective luminance also dependent on viewing angle. The Display++ and VPixx are less strongly affected by this peripheral decline in luminance, and provide hardware based methods that partially compensate for luminance anisotropies in the vertical axis. All consumer-level and gaming LCDs showed difficulties in generating reliable temporal precision: (1) they were unable to reach the requested luminance within a single frame; and (2) they showed temporal dependence, meaning that the luminance of one frame affects the subsequent frame. The Display++ and VPixx were better in this regard, but care needs to be taken when calculating the actual duration of single-frame stimuli as the hardware mechanisms that control light generation and light transmission cannot be perfectly synchronized. We emphasize that depending on the type of experiments, extreme caution should be taken in selecting any LCD monitor to replace a CRT; however, we are confidently using the vision-science specific LCDs for electrophysiological and psychophysical studies.

We measured the temporal and spatial luminance characteristics of one cathode ray tube (CRT; Sony CPD-G520) and five liquid crystal display (LCD) monitors (Table 1). The CRT was purchased new in 2001 and has been used for occasional vision-science testing since that time. All electron guns are functional and focused. Our test set included LCDs made specifically for vision science experiments (VPixx ViewPixx 3D Lite and Cambridge Research Systems Display++), high-end gaming monitors (Samsung 2232RZ and EIZO FG2421), and a consumer-grade monitor (Dell 2209WA). All monitors were purchased by the authors, and the authors have no affiliation or association with any of the manufacturers.

Visual stimuli were generated using an NVIDIA GeForce GTX 650 graphic card (memory 4 GB; 8 bits color resolution) under the control of MATLAB with the Psychophysics Toolbox (Brainard, 1997; Pelli, 1997b) in 32-bit Microsoft Windows. Luminance measurements were made in three ways: (1) using a computer-controlled spectrophotometer placed flush against the screen to block any stray light (i1, X-Rite); (2) a monolithic photodiode placed on the screen (Opt101, Burr-Brown Products, Texas Instruments); and (3) a spot-photometer with 1/3° acceptance angle (LS-110, Konica Minolta).

The spectrophotometer returned luminance measurements in CIE Lxy color space as well as raw spectral data between 380 and 730 nm at 10 nm intervals. Prior to experiments, the sensor was calibrated using a standard white calibration plate.

The photodiode voltage output was monotonically related to luminance and was used for temporal characterization of each monitor. The output was amplified and sampled at 30 KHz (Cereplex Direct, Blackrock Microsystems).

The spot-photometer was mounted on a tripod 1 m from the screen and was used to measure the luminance at the center of each monitor at viewing angles spanning 0–45° azimuth, 0–30° elevation.

The default settings of monitors for brightness, contrast, and color were used for all measurements, with no gamma correction. We also used the native display resolution (Table 1) for each monitor during the measurements. All tests were performed in a dark room with no other sources of light. All luminance stimuli were presented to the full screen, apart from the test of spatial independence.

The most basic requirement of an experimental monitor is that it reliably generates a range of luminance levels. To assess luminance variability, we presented (nominally) uniform, full screen images with 32 gray levels from black (i.e., RGB = 0, 0, 0) to white (i.e., RGB = 255, 255, 255). Each image was presented for 1 s and spectral data was collected using the X-Rite i1Pro positioned at the center of the screen, beginning 50 ms after the luminance change. Gray-level was sequentially increased, with each luminance ramp (32 gray levels) repeated six times. The CRT was turned on for 30 min before testing, minimizing variability due to warming up (Klein et al., 2013).

An ideal vision science monitor must be spatially uniform; that is, the luminance produced for a given input intensity should be the same at all positions on the screen. To characterize spatial inhomogeneities in luminance, we repeated the assessment of luminance variability describe above but made measurements at nine equally spaced positions and with only three stimulus levels (black, mid-gray and white). The nine positions were chosen as the centers of a 3 × 3 uniform rectangular grid tiling the monitor.

In many vision science experiments, viewing distances of 300–570 mm are used, meaning that the projection angle of a pixel to the retina changes substantially across the monitor. For example, at the commonly used viewing distance of 570 mm, the Display++ (which spans 395 × 705 mm), the images span ~38° × 64°. For an ideal monitor, the incident luminance should not depend on viewing angle. We measured the luminance at the center of the screen with a spot photometer under three sets of conditions: (1) four azimuth angles (0°, 15°, 30°, and 45°) with 0° elevation; (2) three elevation angles (0°, 15°, and 30°) with azimuth 0°; (3) three elevation angles (0°, 15°, and 30°) with azimuth 45°. Note that the distance of the photometer from the monitors was fixed at 1 meter in all conditions.

Ideally, changing the luminance in one part of the screen should not affect the luminance in other parts. Although LCDs allow the luminance of each pixel to be independently defined, we examined how changes in luminance across a large number of pixels affected distant parts of the monitor. We measured the luminance of a 400 × 400 pixels image with constant mid-gray (RGB = 128, 128, 128) at the upper-left corner of the monitor (using the X-Rite i1Pro) while the rest of the monitor was changed between black and white every second.

To test the temporal precision of each monitor, we presented full screen white images (i.e., maximum intensity) for one or two frames, with an intervening black screen (i.e., minimum intensity) for 1 s. Each flash duration was repeated 100 times and the temporal changes in luminance were measured using an analog photodiode placed at the upper-left corner of the monitor, sampled at 30 KHz. We focused on testing the timing of black-to-white transitions, as these are commonly used in our electrophysiological and psychophysical testing. Note that black-to-white transitions are not necessarily slowest, as gray-to-gray transitions can take longer in some situations (Elze and Tanner, 2012).

The spatial and temporal specifications of each monitor are summarized in Table 1, along with the maximum and minimum luminance measured in the center of the monitor. All monitors allow an acceptable range of contrasts (>98%); however, the Dell and Samsung monitors may be inappropriate in some situations as their minimum luminance exceeded 1 cd/m2, leading to minimum contrasts of 98.4% and 98.5%, respectively.

Ideally, monitors should generate constant luminance output for a given input intensity across stimulus repetitions. We examined the variability in each monitor"s luminance output across a range of stimulus gray levels. The average normalized luminance and coefficient of variation for 32 equally spaced gray levels are shown in Figure 1. All luminances are normalized relative to their maximum value (Table 1).

Figure 1. Normalized luminance output (A) and variability (coefficient of variation; B) across 32 gray levels of input stimulus for six monitors. The Display++ incorporates manufacturer-implemented gamma correction, providing linearized output. All other monitors were tested in their default mode, without gamma correction.

All monitors were highly reliable (i.e., low coefficient of variation) in generating high luminances, but became more variable at lower luminances. This variability was essentially absent in the Display++, but was a marked problem for the CRT. The variability in the EIZO, evident at low luminance, is unlikely to be a practical problem as the EIZO had the darkest “black” and therefore the range of absolute luminances at this low intensity remains very small.

First, we measured the luminance in 9 equally spaced positions across three stimulus levels (black, mid-gray, and white) for full screen images. Figure 2 shows luminances normalized relative to the mean luminance recorded across all positions for a given input intensity. Surprisingly, even with a black stimulus the luminance pattern was not spatially uniform in three monitors (CRT, Dell, and EIZO). With gray and white stimuli, the EIZO, Samsung and Display++ showed up to ±20% variation in luminance across positions, with the center of the monitor markedly brighter than surrounding regions. The CRT also showed luminance variations, but this may be partly attributable to the age of the monitor (manufacture date, March 2001) and was primarily evident at extremely low mean luminances (0.04 ± 0.03 cd/m2) suggesting it will have no practicable effect on perception. The Michelson contrast for each gray level is indicated for each monitor, and was just 0.023 for the VPixx when presenting white, suggesting that it is effectively spatially-invariant.

Figure 2. Uniformity of spatial luminance. Mean luminance (n = 6) across 9 monitor positions measured with the screen showing black (A), mid-gray (B) and white (C). Note that the heatmaps in each panel have different scaling. All luminances are expressed as a percentage of the mean across all spatial positions for a given monitor (i.e., 0 = mean luminance). The blue number next to each panel indicates the Michelson contrast for each gray level.

Next, we examined a different kind of spatial uniformity by measuring the luminance at the center of the monitor from different viewing angles (Figure 3A). The values in the figure have been normalized relative to that measured at azimuth 0°, elevation 0°. While the CRT was nearly view-invariant, the measured luminance of all LCDs depended strongly on viewing angle. As examples, at azimuth 45° and elevation 0°, the measured luminance ranged from 50 to 80% of that measured with a frontal viewing angle [0°, 0°], and with viewing angle [45°, 30°] the measured luminance with three monitors was less than 30% of that with a frontal viewing angle.

Figure 3. The dependence of measured luminance on viewing angle. (A) Different azimuth and elevation angles. The first value in the brackets indicates the azimuth and the second indicates the elevation. Each arrow shows the position and the angle of spot-photometer. (B) Normalized luminance at azimuth angles of 0–45° with elevation 0°. The results are the average of 4 measurements, normalized to the maximum luminance of each monitor measured with azimuth 0° and elevation 0°. (C) Normalized luminance at elevations of 0–30° with azimuth 0°. (D) Normalized luminance at elevations of 0–30° with azimuth 45°.

The combination of LCDs having brighter centers than surrounds, and luminance falling off with increasing viewing angle means that spatial anisotropy needs to be taken into account when large, or peripheral stimuli are presented. Figure 4 simulates the combined effect of using a monitor with a brighter center (Figure 2) and oblique viewing angles (Figure 3) for three peripheral positions and angles. A viewing distance of 570 mm is assumed here, however, the influence of viewing angle will increase as viewing distance decreases. To this end, we calculated the viewing angles of three points: (1) on the horizontal meridian of the monitor, one-sixth of the monitor"s width from the monitor edge; (2) on the monitor"s vertical meridian, one-sixth of the height from the top; and (3) one-sixth of both the width and height from the monitor edges. Then, the (normalized) luminance expected at each point for an observer directly in front of the center of the monitor was estimated by multiplying the effects of viewing angle and spatial anisotropy across the monitor surface.

Figure 4. Effect of spatial luminance variations combined with viewing angle. Each colored circle shows relative luminance at a peripheral screen location, assuming a viewing distance of 570 mm. Positions are indicated in the representation of the monitor (inset), and were one-sixth of the monitor width and height from the right and top edges.

By this measure, the CRT performed well, with minimal effective luminance drop from the center to the three peripheral regions. The effective luminance of all LCDs, however, decreased substantially in the periphery, with stimuli in the upper-right corner of the screen having as little as 25% of the luminance at the center of the monitor (blue circles in Figure 4). As discussed below, the VPixx and Display++ have hardware based mechanisms that can compensate for vertical luminance anisotropy by using a brighter backlight at the top and bottom of the monitor. This mechanism cannot compensate for horizontal anisotropies as the LEDs are arranged along the side of the monitor and illuminate entire rows of pixels.

For the final test of spatial characteristics, we measured the spatial dependence of luminance, i.e., the extent to which modulation of one part of the screen affected other parts of the screen. For all monitors, the luminance of a gray region was significantly affected by the luminance of adjacent regions (Figure 5), with the smallest effect size still d = 1.77 (where Cohen"s d is the difference between the two means divided by the pooled standard deviation). Surprisingly, the directionality of this effect was variable: the luminance of the gray region was significantly higher (brighter) when other parts of the monitor were white vs. black in four monitors, and significantly lower (dimmer) when surrounded by white vs. black in two monitors. Fortunately, the absolute variations in luminance were typically less than 1 cd/m.

Figure 5. Luminance spatial dependence. (A–F) Measured luminance of a gray image when the remainder of the monitor was black or white for CRT (A), Dell (B). Each dot indicates an independent luminance measurement. Error bars show the mean and standard deviation. Mean luminances in the black and white conditions were significantly different for all monitors (Wilcoxon rank sum test, p-values at the top of each plot), with large statistical effect sizes (d′) but small differences in absolute terms.

An ideal monitor should: (1) reliably reproduce a temporal luminance profile across multiple repetitions; (2) instantly and accurately update the luminance at any position on the monitor; and (3) generate a luminance that is independent of previously presented luminances. Figure 6 shows the temporal dynamics of luminance changes for 100 repetitions of a stimulus comprising a white screen presented for either one or two frames, following a 1 s period of black. White stimuli presented for three or more frames were not noticeably different from two-frame stimuli. The CRT represents the “gold standard”: the luminance profile within a frame rises rapidly to a peak; this peak luminance is independent of the luminance in earlier frames; and the luminance profile is reliable across stimulus repetitions (Figure 6A). All LCD monitors deviated from the benchmark, with the VPixx showing the best overall performance.

Figure 6. Temporal profile of luminance “on” and “off” luminance steps. (A–F) Each plot shows the temporal changes during 1 (green) and 2 (blue) frames of white stimuli over 100 repetitions, overlaid on each other. Each frame of white stimulus is indicated by the shaded regions (light gray: first frame, dark gray: second frame). The red arrow (C) highlights a luminance bump due to the use of Turbo-240 mode, which effectively runs the monitor at 240 Hz, with every second frame displaying black.

For all LCD monitors except the Dell, there was little noticeable variability in the temporal luminance profile, highlighted by the fact that the overlayed traces from 100 stimulus trials are almost indistinguishable (Figures 6B–F). The Dell monitor was highly variable across stimulus repetitions and flickered in luminance even within a single frame.

All LCDs showed some level of luminance hysteresis when stimuli were changed from black to white, or white to black (Figure 6). Starting from a black screen, all LCDs were unable to reach their maximum luminance in a single frame. Due to the range of backlight mechanisms implemented in the monitors, we have not attempted to quantify the rate of increase or decrease in luminance. The Display++ and VPixx, however, had the best performance as the luminance: (1) rose to close to its peak for any given frame within <2 ms; and (2) rose close to the peak possible luminance on the first frame of a white stimulus following black. Note that the step-like luminance transitions evident with these monitors reflect the progressive illumination of different LEDs associated with the scrolling backlight mode. After two frames of white, the Dell and Display++ were the only LCDs unable to switch back to black within a single frame. This is evident as the non-zero luminance bumps after the gray-shaded regions in Figures 6B,E (from 35 to 40 ms for the Dell and 18–20 ms for the Display++). For these monitors, the first black frame following a white frame would appear as gray. Note that in the case of the Display++, this extra flash appeared regardless of whether the monitor was run in strobing or scrolling backlight mode. Collectively, the hysteresis effects cause two problems: briefly presented luminance increments (e.g., black-white-black) last one frame longer than desired, and transitions between extreme stimulus levels (e.g., black to white) do not occur within a single frame. One observation warrants special attention—the EIZO had a luminance “bump” in the first white frame that is only evident when two or more white frames are presented (arrow in Figure 6C). This is due to the use of “Turbo 240” mode, which uses an effective backlight frequency of 240 Hz.

We assessed five LCD monitors in order to determine if their temporal and spatial characteristics make them suitable replacements for CRT monitors in vision research. In our spatial tests, we measured how luminance varied across repeated measurements, spatial position, spatial context (i.e., the luminance of surrounding pixels), and viewing angle. In our temporal tests, we examined how reliably each monitor could produce luminance changes across consecutive frames. We did not assess the chromatic properties of each display. Our spatial and temporal measurements confirm the known limitations of CRT and conventional LCD monitors. However, we demonstrate that under some circumstances, some high-end gaming monitors meet the temporal demands of vision research, and recently available professional LCD monitors can replace CRTs in vision laboratories for most experiments.

All LCD monitors had reproducible outputs, although the luminances did not always match the desired values when short duration stimuli were used. Two monitors (the Dell and Samsung) were problematic in that they had noticeable light emission (>1 cd/m2) even when a black stimulus was presented. This is undesirable because it limits the peak contrast of the monitor. The Display++ benefits from a built-in gamma correction mechanism, which means there is a linear relationship between the drive stimulus and the screen luminance, and luminance variability is proportional to mean luminance across all drive levels.

All LCDs except the VPixx had poor spatial uniformity, with the center typically the brightest position on the monitor. This limitation has previously been reported for both CRT and LCD monitors (Metha et al., 1993; Bohnsack et al., 1997; Krantz, 2000; García-Pérez and Peli, 2001; Klein et al., 2013). The remarkable uniformity of the VPixx reflects that it is designed specifically for experimental use; with other monitors, the inhomogeneity must be taken into account when the aim is to present stimuli with identical luminance and contrast at different spatial locations. Although the Display++ and VPixx both have hardware-based mechanisms for correcting vertical inhomogeneities in luminance output, a more general solution would be to use software-based corrections to the image intensities passed to the video card (e.g., by parameterizing the full input-output relationship across space, analogous to traditional gamma-correction).

While CRTs have little appreciable change in luminance across a wide range of viewing angles, for all LCDs, increasing the viewing angle to more than 15° in either axis (azimuth and elevation) greatly decreased the measured luminance. This reflects a major shortcoming of LCD technology, which is also evident in modern commercial displays based on organic light emitting diodes (OLED displays) (Ito et al., 2013). Surprisingly, the cheapest Dell LCD was the least affected by viewing angle, which may make it a convenient choice for presenting static images. With small viewing distances, the effects of viewing angle combine with the drop-off in peripheral pixel luminance, such that if a subject looks at the upper-right corner of the screen from the center with viewing distance of 570 mm, the luminance fall off for LCDs is huge (almost 80% for EIZO and 40% for VPixx relative to center). This dramatic luminance drop must be taken into account when stimuli are presented in peripheral regions.

Spatial dependence is commonly tested by comparing the spatially-averaged luminance of horizontal and vertical gratings comprising alternating black and white pixels. CRTs “fail” this test as vertical gratings have lower luminances than horizontal gratings (e.g., Pelli, 1997a; Krantz, 2000; Wang and Nikolic, 2011). LCD technology overcomes this problem as it independently addresses each pixel, making the monitor spatially independent. However, here we took another approach and measured the interactions between large regions of the monitor. In all LCDs, we observed that even slow modulations in one area of the monitor from black to white caused significant luminance changes in other regions. However, it should be noted that the absolute changes in measured luminance were very small and therefore this effect can probably be ignored.

The temporal characteristics of a monitor can be assessed by examining: (1) whether the requested luminance is reached within a single frame; (2) the reliability of temporal luminance patterns across multiple repetitions; (3) the independence of luminance in consecutive frames; (4) the rise and fall times associated with luminance changes within a frame. We measured the first three of these characteristics, but it was inappropriate to compare rise and fall times due to the different light sources and modes of illumination in each monitor.

Our measurements show that the CRT and the VPixx satisfied all temporal factors; both provided highly reliable luminance profiles within a single frame and minimal interaction between consecutive frames. However, our results suggest that most consumer-grade and gaming LCD monitors cannot safely be used for all experiments requiring temporally-precise stimuli. For example, the Dell LCD exhibited multiple luminance alterations within a single frame (with frequency of ~240 Hz) due to the backlight controller. Luminance output for this monitor was also highly variable across repetitions, did not reach the desired maximum luminance even after the second frame, and was very slow at falling to baseline luminance at the end of a frame.

The Samsung LCD has been described previously as a monitor suitable for vision science (Wang and Nikolic, 2011), and we found it to be highly reliable and temporally precise. However, as it has continuous light emission, it implements “sample and hold” style stimuli, which will lead to blur artifacts when using moving stimuli. Thus, the Samsung is appropriate for stimuli requiring high temporal precision such as flashes and reverse correlation, but not motion.

The Display++ and EIZO LCD exhibited interactions between the luminance of consecutive frames. Although this interaction may have minimal perceptual effect, it cannot be easily neglected in physiology experiments, as it would likely be detected by neurons early in the visual processing hierarchy (De Lange Dzn, 1954; Smith et al., 2001). A number of factors could ameliorate this problem. First, in our tests, we used stimuli that changed from minimum to maximum intensity, which require the largest state change in the liquid crystals. Using lower contrast changes (e.g., 10% or 50%–90% luminance) should allow faster switching. Second, given that our results suggest that the timing of these monitors is highly reliable, their imperfections could be incorporated into most experimental designs. Finally, the timing and intensity of the backlight in the Display++ and VPixx is user-configurable. The backlight comprises 32 LEDs along the left side of each monitor, which can be strobed simultaneously or illuminated sequentially in a scrolling manner. Illuminating a given LED as late as possible after the corresponding row of pixels has been updated is the best way to minimize luminance cross-talk between frames.

Table 2 summarizes the strengths and weaknesses of each monitor. In our opinion, none of the consumer-level or gaming LCDs can safely be used as a replacement for a CRT in all vision science experiments. Provided motion stimuli are not required, the Samsung provides excellent temporal fidelity and continuous light output. Provided the luminance-interaction between frames is incorporated into stimulus