CRT vs LCD

Contents

  1. Introduction
  2. Equipment
  3. Criticisms Of LCD TVs
  4. Criticisms Of LCD Monitors
  5. Health & Safety
  6. References

1  Introduction

These pages compare CRT and LCD display technologies as rationally and scientifically as possible within the constraints of a domestic environment.  They were prompted by repeated postings with no supporting evidence, in news groups such as uk.tech.broadcast and uk.tech.digital-tv, that CRTs are superior to LCDs, whereas my own experience is precisely the opposite.  Where possible I supply or quote objective or independent evidence, otherwise I report my own experience, accepting that, unlike evidence, my experience is simply hearsay to others.

The sources of questions and criticisms mostly fall into two groups:

Domestic Users

Either they are researching buying a new TV, in which case these pages may help, though primarily I would recommend Choosing A TV, or else are seeking further explanation as to why such a purchase, perhaps made after inadequate research, hasn't turned out as well as hoped.

With the latter, a typical scenario seems to be that a former analogue narrow screen (4:3 aspect ratio) CRT, which was aging before it broke and therefore had possibly drifted out of adjustment, is replaced with a much bigger wide screen (16:9 aspect ratio) LCD.  Because of a combination of …

… defects are visible which previously were not, and the new TV is blamed.  In fact most, very probably all, will turn out to be in the digital broadcast signal  in the UK, digital signals are so over-compressed that only 1 to 3% of the original data captured by the camera ever arrives at the TV!

Broadcast Professionals

Typically broadcast professionals simply state, as assuredly as it was once claimed that the sun went round the earth, that CRTs are much better than LCDs.  When challenged to supply supporting evidence, either none is forthcoming, or it is at best corporate hearsay, at worst pseudo-science.

The problem with corporate hearsay is that corporations have enormous inertia  a culture of jargon, work practices, standards, etc  that can be immensely difficult to change, and keeps them working in a certain way even though it may be shown to be based on a falsehood.  Hence, for example, it is still common for people in the moving arts and visual display industries to refer to "persistence of vision" even though the concept was shown to be false as long ago as the 1970s1.

The most assured way of keeping abreast of new technology, and, a significant point, having an input into its design at an early enough stage for your industry to get what it requires of it, is to conduct trials.  Strange as it seems to someone like myself of technical background, formerly employed to conduct such trials in furtherance of a firm's business, it does genuinely seem that noone has actually assessed LCD technology in such an independent, scientific, and rational way.  Certainly, repeated requests have failed to elicit even a quote from the results of such a trial, let alone a full technical report, and repeated searches have failed to find any published results, even from 'open' organisations such as universities, technical colleges, the EBU, or the BBC.

2  Equipment Used

Naturally, I would have preferred to perform the sort of corporate trial discussed above, but this would have required access to a range of equipment that I do not have, and consequently, these documents can not and do not claim to be results of such a trial.

Instead, I have had to be content in making as impartial a comparison as possible using what I happen to own, being two ordinary televisions of similar size.  To estimate how more widely applicable these results might be, I've spent much time searching for relevant data, completely without success for CRTs, and SD LCD data is also getting difficult to find now that HD is sweeping the market.  The best that I can say is that while I have no reason to believe these TVs are unusual or atypical, they are probably not absolutely typical either, and one of each type is inadequate as a statistical sample.  Hence, care should be taken in generalising from the following results!

Nevertheless, at least they are useful, demonstrable results, whereas, as far as I am aware, there is nothing scientifically robust coming from the pro-CRT side.

Unless otherwise indicated, the two televisions used were:

TypeCRT (aperture grille)LCD
Model Sony KV-16WT1U Panasonic TX-15LT2
Size, Nominal Size (mm, in) 365, 14 385, 15
Screen Width (mm) 317 ±1.5 338 ±1
Screen Height (mm) 179 ±1.5 192 ±1
Measured Phosphor/Element Pitch (mm) 0.614 ±0.014, NA 0.390 ±0.014, 0.390 ±0.014
Calculated Effective Resolution 516 ±15, NA 867 ±35, 492 ±35

Notes:

  1. Ideally the televisions would have exactly the same screen size, the actual difference is roughly 5%.
  2. Neither TV has sufficient resolution to display SD at 720×576i  it's not meaningful to talk of vertical resolution with an aperture grille design, but the CRT's 72% horizontal coverage might be expected to lose picture detail more significantly than the LCD's 85% vertical coverage, and this is the most probable explanation for the results actually obtained favouring the LCD.
  3. The CRT has a scratch on the screen, but it does not feature in any picture fragment used here.
  4. LCD technology being much dimmer than CRT technology, in order to obtain adequate exposures, the LCD's Backlight and Brightness controls had to be set to their maximum values (in normal viewing they would both be at 50%).  All other controls on both TVs were set for normal viewing, in particular all 'Artificial Intelligence'& signal processing options were disabled.

Photographs were taken by a Canon S40 camera mounted on a mini-tripod so that the lens was as near as possible opposite the middle of the screen, error < ±15mm, with a lens to screen distance of 300±5mm.  The camera settings were:

Note that there are dead pixels in the camera, appearing as, mostly, red dots in some of the images here.  These can be demonstrated to lie within the camera because they are always in the same pixel positions.  As they have nothing to do with either television, they should be ignored.

The resulting *.CRW (Canon Digital Camera RAW file) photographs are each about 3-4Mb in size, but are not understood by web browsers, and hence have had to be converted via TIFF to PNG format of about half the file size.  I did not discern any loss of detail in this conversion.

Composite video was chosen as the format for the source signal as this could be duplicated easily by a Quintro+ B-Tech BT945 SCART Switch via its two RCA composite video outputs.  The TV2 switch on the unit was not depressed, and no channels were locked, which meant the TV1 and TV2 outputs were showing the same source signal.

3  Commonly Voiced Criticisms Of LCD TVs

Criticisms of LCDs that are commonly voiced include:

  1. Artifacts introduced by motion

    Please see the original experiments ...
    1. Photographic Comparison Of Output
    2. Ancillary Demonstration Of Artifacts

  2. Artifacts introduced by deinterlacing

    While it is known from the way CRTs work that most display each picture line as it is received, with LCDs there's a shortage of facts  it can be deduced from specifications that at least some recent High Definition TVs can deinterlace, but this appears to be an option selectable via menu rather than default behaviour; sources such as Wikipedia explain different deinterlacing methods2, and claim without convincing evidence that all non-CRT display types require deinterlacing3; others are more equivocal4:
    I've just had a very interesting chat with a guru within my company who deals with such matters.  The short answer is that no one knows for sure how the processing is performed.  You'd have to ask each individual manufacturer how they do it.

    One thing is certain however, he has witnessed tests of many different types of screen all being fed with exactly the same signal.  There are huge differences with temporal resolution, so the processing techniques are very different from mfr to mfr.
    Interlacing - LCD There is also this image which is from an interlaced analogue signal source displayed on my 22" LCD.  If the LCD was deinterlacing it, you'd expect that lines would be paired, and that each pair would contain either identical content averaged over the pair, or interpolated content over the pair.  Although superficially the lines look paired, they are neither averaged, individual lines in each supposed pair differ noticeably, nor interpolated, the edge of the person's arm in the upper line in each supposed pair seems if anything sometimes slightly to the left of the lower, whereas interpolation would place it about two pixels to the right, an unmistakable difference.  Alternate lines also have a slightly different colour rendition.  Hence, it seems that the picture contains two fields shown as such, and this LCD is not deinterlacing.

    In fact, I believe it makes more electronic and economic sense to assume that most LCDs buffer rather than deinterlace.  To understand the difference between the two and why, the following must first be understood: This being so, and deinterlacing circuitry being relatively complex and expensive, I cannot see why an LCD manufacturer would choose to increase the cost of its units by attempting to deinterlace the signal, when they have no way of knowing whether a given signal being displayed was originally progressive, in which case a slight improvement would result, or interlaced, in which case a significant degradation would result.  It just wouldn't make economic sense.  Some high-end LCDs appear to attempt it as a menu option, but I'd be surprised if the majority do it.  I suspect that those sources that make these sweeping claims are actually confusing deinterlacing with buffering, a suspicion reinforced by the lack of any supporting evidence that stands up to logical examination.

  3. Jaggies

    It is claimed that LCDs show more jaggies than CRTs.  Simply, this is a myth:
    CRT LCD
    Jaggies - CRT Jaggies - LCD
  4. Lack of contrast ratio

    I have satisfied myself that this criticism does have some foundation in fact, at least as far as my own LCDs are concerned, but the differences are only discernible in unusual situations  night time CCTV, some night scenes in B&W movies, star- and galaxy-scapes in astronomy or sci-fi programmes, etc.  Further, CRTs commonly need adjustment of the Brightness to see such scenes optimally.  What's really needed is a display technology with sufficient contrast ratio for this to be unnecessary, and neither CRTs nor LCDs are really adequate in this respect.  Consequently, I do not intend to discuss this further here.

  5. Colour characteristics such as gamma

    As this is an issue for production rather than domestic environments, I shall not discuss it here.

4  Commonly Voiced Criticisms Of LCD Monitors

Criticisms of LCD Monitors that are commonly voiced include:

  1. Colour Rendition

    This shouldn't happen if monitor drivers are correctly installed.  If required for correct colour rendition, monitors of any type should include an ICC Profile5 (*.icm) in their driver set.  Perhaps those reporting this problem are not using the correct drivers, but instead general purpose drivers such as Default Monitor.

  2. Fonts - LCD Font Rendition

    In my experience this is a myth.  Regardless of monitor type, the most critical factor for fonts is the aspect ratio of the resolution being displayed  if this is 4:3, fonts look fine, but the further it departs from 4:3, the worse they look.

    A subsidiary claim is that on an LCD fonts only look 'right' at its 'native' resolution, but a CRT has no such constraint.  Again, in my experience, this is a myth  the native display resolution of my ViewSonic VG712s monitor is 1280×1024 (not even 4:3, which alerts the sceptic in me), but the accompanying photograph shows some text displayed in 1024×768, and there is no discernible degradation of the text.  Besides the importance of having the correct monitor drivers, it is also necessary to have the correct settings under Start, Settings, Control Panel, Display, such as: For example, the default refresh offered is often 75Hz, which in my experience will usually display a picture on an LCD, but it is sometimes misshapen and distorted, while 70Hz is always excellent.

5  Health And Safety

  1. X-Radiation

    CRTs are inherently a mild X-ray source.  Consequently, increasingly stringent standards for computer equipment have resulted  MRP-II, TCO-*6; I am not aware of any relevant international TV standards.  Though nowadays the radiation doses given out are very low, they still have some significance.  Those purchasing a new CRT monitor or TV may care to note that an average year of CRT TV watching is roughly equivalent to a year living next door to a normally operating nuclear plant7.  This may seem trivial, but children regularly sitting for hours on the floor too close to a CRT TV or anyone constantly sitting in front of a CRT monitor probably represent significantly higher doses than average, and any X-ray exposure, particularly to children, seems senseless when it is entirely avoidable by using LCD technology.

  2. Eye-Strain

    There are hearsay reports of CRTs being more tiring on the eyes, to which their adherents often reply that the refresh rate was probably too low.  In the absence, as far as I am aware, of conclusive and rigorous test results, I can only add to the hearsay.  My experience is that refresh rate makes little difference above a certain level, probably somewhere between 50 to 100Hz depending on the individual, yet CRTs still tire the eyes above this level, whereas I have never noticed any adverse effects from using LCD monitors, even though on a daily basis I use them for hours without break.  Further, I'd like to add the following …

    About a decade ago, I lost control over my immediate work environment for two years, and had to sit closer to my CRT monitor than I really wanted to  my eyes were probably about 0.5m or less away from the screen, whereas before and since I've always worked at 1m.  During that time I would feel tiredness in my eyes within a short time of starting work, much sooner than previously.  Also over that time my eyesight rapidly deteriorated to the point where I now need glasses to read small print.  It could be argued that this was natural ageing, and I couldn't disprove that, but my own feeling based on the timing and rapidity of the deterioration is that the major cause was that particular desk layout causing the closeness of the CRT.  By contrast, I've been able to keep the same glasses ever since I started using LCDs.

6  References

  1. <a href="http://academic.evergreen.edu/curricular/emergingorder/seminar/week_1_anderson.pdf" target="_top" title="academic.evergreen.edu">The Myth Of Persistence Of Vision Revisited, Journal of Film and Video, Vol 45, No 1 (Spring 1993), 3-12</a> (link now dead)
  2. Wikipedia, Deinterlacing
  3. Wikipedia, Interlacing
  4. uk.tech.digital-tv, LCD vs CRT resolution, 11/8/2008
  5. Wikipedia, ICC Profile
  6. <a href="https://en.wikipedia.org/wiki/TCO_Certification" target="_top" title="Wikipedia">Wikipedia, TCO Certification</a> (link now dead)
  7. Radiation Exposure
Updated Description
08/11/2009 Added this update table.
31/07/2009 Updated contents of 'Artifacts introduced by deinterlacing'.
15/02/2009 Created this page and made original pages subdocuments of it.
11/02/2008 Original pages brought into rest of personal website.
16/01/2008 Added Ancillary Artifact Demonstration.
10/01/2008 Created original Photographic Comparison Of CRT & LCD TV Output.