Talk:Cathode ray tube

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Former good article nominee Cathode ray tube was a good articles nominee, but did not meet the good article criteria at the time. There are suggestions below for improving the article. Once these issues have been addressed, the article can be renominated. Editors may also seek a reassessment of the decision if they believe there was a mistake.
June 12, 2007 Good article nominee Not listed
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Older Comments[edit]

since someones mentioned not messing with a CRT, should it be mentioned that one should short the large capacitors to avoid a shock

I've just added:

These high voltages can persist long after the device containg the CRT has been switched off.

In general, the untrained shouldn't be opening the box in the first place, and providing warnings is better than providing "how-to" details: where do you stop?

To do:

The line "CRT is a triode. More complex CRTs contain greater numbers of electrodes. " was deleted. Primarily, this makes no sense logically, and also, triodes were mentioned later.

Sounds good to me, welcome to Wikipedia. -- Tim Starling 07:47, Jan 5, 2004 (UTC)

CRT illustrations made especially for Wikipedia[edit]

Hi - danish wikipedian here.
For some snazzy illustrations, check out the danish article (language: "Dansk") on the subject: I just rendered some "cut-away" images of various CRTs...

User:Peo on danish Wikipedia

... and now I've moved large versions of those illustrations onto Commons. See:

User:Peo, from danish Wikipedia - again!

How many joules are in the capacitors? lysdexia 22:18, 19 Oct 2004 (UTC)

"...children should even be encouraged to do this so that they may see the immediate and dramatic effect of a magnetic field on moving charged particles, provided they are informed to never do the same with a color tube."

TEACHER: So remember, kids, never put a magnet near your TV or you'll mess up the screen.
JOHNNY (THINKS): Gee, that's great! If I mess up our crappy old TV Dad'll have to get a new one! Lee M 01:59, 2 Dec 2004 (UTC)


I wonder if *THAT* is what happened to my crappy old 13" TV? :)

Seriously, the Exploratorium has a color TV and a huge magnet set up for just this sort of playing around.

Meanwhile, [[User::lysdexia]] asks about how many joules are stored. Well, Joules = KV^2 * uF, so lets take a SWAG and call the CRT 0.01 uF. Meanwhile, the charge on the CRT can be 25 to 30 KV on a modern color CRT so we can calculate 6.25 to 9.00 Joules based on our SWAG about the capacitance. Having been on the receiving end of a 17KV discharge from an old B/W CRT (never grab the 1B3GT by the bottom; you might contact the HT pins!), I say that sounds like it's in the right ballpark. The shock wasn't too bad, but I really hurt my elbow when it smashed into the wall behind the TV set.


Controlling pixel brightness[edit]

There is no information in this article on the way the brightness of pixels is controlled. There is a great deal of public confusion about this matter. Is the power of the electron gun modulated, or is there a grid to control power as in the basic triode vacuum tube? I see that there are other patented methods for fixed-power electron guns in CRTs.

The question arises in the context of, where some sites claim measurements of decreased power for a nearly-all-black screen, and some claim increased measured power--on different CRTs, of course.

CRT Resolution[edit]

I imagine a black-and-white CRT, which has no fixed pattern of pixels, would be able to adjust vertical resolution (number of lines) by changing the synchronization. As for the horizontal resolution, it depends mostly on the electronics and the focusing ability of the electron gun. Otherwise, there are no pixels in B&W CRTs.

This is however not true about color CRTs which, just like LCDs, have a fixed pattern of pixels--both because of the fixed pattern of color phosphor dots on the screen, and because of the fixed pattern of holes in the grille.

So, even though you might theoretically get better resoulution watching 480p DVD on a black and white CRT (provided your electronics supports this), you won't have the same advantage on color screens. I propose to remove this part from the article.

Bartosz (talk) 21:27, 1 January 2008 (UTC)

The dots on the shadow mask aren't subpixels, because the brightness must not be constant over the whole dot (which you can sse i.E. on File:Aperture_grille_closeup_teletext.jpg). You can increasse the resolution indefinitely in theory, although the picture won't look very good, if the resolution is much bigger than the hadow mask resolution, because this will make some subpixels be absorbed by the aperture grille (I dind't notice this effect using 2048x1536 on my 22" CRT, which has 20" visible and an aperture grille (better known as trinitron, which is actually a brand name by sony) w/ 0.24mm, which would match a horizontal resolution of 1924 pixels in the visible part of the tube and because it's an aperture grille, there is only a horizontal arrengement, not a vertical, so the vertical resolution is really unlimited). You actually can't exactly match the shadow masks resolution, because CRTs don't have a fixed size of the image, normally you make the image somewhat smaller then the CRTs size, because the visible size of the tube is normally about 1"-2" smaller than the actual size. But i.E. if you have a 19" CRT w/ 0.23mm dotpitch, you will have about 1679x1259 dots (or about 1600x1200 in the visible part, if about 18" are visible), but the picture won't look better, if you use 1600x1200 than w/ i.E. 1024x768. If you use 1024x768 on a 1600x1200 LCD the picture will look much worse than w/ 1600x1200. --MrBurns (talk) 10:09, 16 February 2009 (UTC)

I think the initial comment is worthwhile, as is this section on resolution. What it lacks is a distinction between mono-chrome and colour. As I understand it:

Horizontal resolution:The horizontal resolution of a mono-chrome (black and white, black and green, amber etc.) is continuous (analog) and hence theoretically infinite. The pracical limit is how fast one can alter the intensity of the electron beam. The horizontal resolution of a colour crt can be said to be fixed, in the sense that it must conform to the pattern of red,blue and green areas applied to the inside of the crt in the factory. It is possible to vary the intensity within each area, although the result is neither a simple increase in resolution, or easy to describe in text.

Vertical resolution. The vertical resolution of a monochrome monitor is theoretically infinite, just as with the horizontal, but one must remember the electron beam and resulting "dot" have width. For colour there are two types of mask to consider. In the first type the coloured areas are not continuous verically, and the resolution is constrained in the same way as the horizontal colour is above. In the second type the coloured areas are continous vertically, and the resolution is not constrained, the the sense of vertical mono-chrome above. This type of crt was introduced and used exclusively by Sony under the name "Trinitron", until the patent expiried, after which many manufacturers used it. Antifesto (talk) 00:00, 20 March 2014 (UTC)

The assumptions expressed here about dot pitch constraining resolution are mistaken.... very common, but mistaken. It is simply not the case that the phosphor triads on the screen match 1:1 (or close to that) with pixels, or that the number of triads constrains the number of pixels that can be displayed.
If that were the case, then on the color CRT you would see very obvious aliasing effects (like moire patterns) when you attempted to use pixel counts that were much higher than about half of the triad count... particularly when you came close to the actual triad count (Nyquist!) To eliminate this you'd have to display exactly as many pixels as you have phosphor triads, and to make that work there would have to be precise synchronization between the electron beams' arrival at the triads and the pixel times in the input signal, and this is just not practical. There isn't even a "dot clock" in the VGA signal, and there is considerable tolerance in the "front porch" duration, so there is really no way to determine just from the sync pulses exactly where each pixel is within the horizontal scan interval. And small adjustments to your H and V size and position controls would throw off the alignment completely. (Those controls do not work in increments of one pixel, or one triad!)
It would also have to be the case that each beam lit up exactly one phosphor dot or stripe at a time, and that isn't true either; electron beams in CRTs cannot be focused that finely.
Instead each beam illuminates a considerable number - a dozen or so - of the dots or stripes of its color (the shadow mask or aperture grille ensures that each beam falls only on phosphors of its intended color, and of course there is some spillover, esp at high beam intensity), with falloff toward the outer edges of the beam. The beam of course sweeps from left to right, and it is varied in intensity according to the input signal. It doesn't matter in the slightest if the beam happens to be "right between two triads" when information arrives for a particular pixel, because what you see as "the pixel" is simply the average of the brightness of the triads in that area. It's all very stochastic. Jeh (talk) 02:48, 20 March 2014 (UTC)
This is fascinating information, but I'm having trouble understanding how the triad density does not constrain horizontal resolution in an aperture grill display. Your description suggests that multiple phosphor triads are energized for each "pixel", but how is it possible to have a horizontal resolution that exceeds the triad density? For example, suppose that there are 1000 triads across the display width. I can't envision how this display could successfully resolve an image that has 600 alternations of red and green lines (e.g. 1200 lines in total).Spacediver (talk) 03:54, 13 July 2014 (UTC)
The resolution cannot exceed the density of the colour phosphor triads. The point is: that for the normally encountered television resolutions, the triad density is larger than the resolution disctated by the bandwidth of the (analogue) signal. Tubes with much higher triad densities were produced for the computer monitor market. They were also developed for television sets designed to display high definition pictures (in both the 720p and 1080i variants), but these never made it to market as they were headed off by flat panel displays. DieSwartzPunkt (talk) 16:42, 13 July 2014 (UTC)
You appear to have missed the point. There will be no moiré effect if you, "attempted to use pixel counts that were much higher than about half of the triad count". This is precisely because the picture in a cathode ray tube is not composed of pixels. All that the density of the colour triads does is to present an upper limit to the (analogue) horizontal resolution of the tube - the vertical resolution being fixed by the scanning lines. DieSwartzPunkt (talk) 16:50, 13 July 2014 (UTC)
No, the density of the triads does not limit the horizontal resolution. And moire patterns don't require pixels.
Consider a monochrome CRT - it has one giant "phosphor dot". Yet it can display many, many details across the width of the screen, no?
If you do the calculations - I have - you'll find that the "dot pitches" on the higher res CRTs weren't really fine enough to support the resolutions they claimed to support. Yet, those resolutions worked, even though according to you they should have been impossible. The reason they work is that Color CRTs never, ever needed to illuminate just one dot triad at a time. The rate of the horizontal sweep and the rate at which the beam could be modulated are what limit horizontal resolution. Jeh (talk) 21:56, 3 June 2016 (UTC)
Conversely, this is why LCD displays with VGA inputs do have fine "sync" and "phase" adjustments. Assuming that the input signal pixel count matches the display resolution, then each pixel on the screen is controlled individually, from the input signal at a time that is assumed to represent the corresponding pixel. Most modern LCDs can do a pretty good job of finding the line rate and the first and last pixel on a line by themselves, but this is very dependent on the image being displayed. If the timing is off by more than a quarter of a pixel or so you will get very obvious moire patterns when displaying fine detail. You just don't see that on a CRT. And that's all the evidence you should need that color CRTs just don't work that way. Jeh (talk) 01:55, 23 March 2014 (UTC)

"Health hazards" section and article organization[edit]

Much of the health hazards section, like the parts about electric shock and audible whine, refer to apparatus containing CRTs rather than to the CRT itself. (A CRT sitting in a box on a shelf may contain some hazardous substances, and presents an implosion hazard, but it's not going to shock anyone or make annoying sounds.) There are similar issues scattered all through the article. Jeh (talk) 22:02, 3 June 2016 (UTC)

They could use clarification, but I wouldn't remove them, if those components are necessary to make a CRT work, or at least were customarily included with them. StuRat (talk) 20:37, 18 July 2016 (UTC)

Decline and Fall of the CRT[edit]

Despite some of the CRT is not dead comments above, here in 2016 the only CRTs I have seen for years have been as ageing railway station displays (I once saw one displaying a BBC microcomputer boot screen well into the 21st century!) For almost all purposes the CRT is dead as a dodo thanks to cheaper and now much better (e.g. wider angle, brighter) LCD technologies. But the article stops charting the demise of the CRT in about 2006. As one of the most profound changes in technology the article really should cover the finalk death throws (and any legacy applications for CRTs) in better detail. Stub Mandrel (talk) 20:21, 18 July 2016 (UTC)

Advantages and Disadvantages Section[edit]

I removed the Advantages and Disadvantages section as it was clearly non-neutral (to such an extent which I doubt anything short of a complete rewrite would fix the problem) and had been flagged as non-neutral and not fixed since 2012. I have no special knowledge about this subject, but a appropriately balanced advantages and disadvantages section could be a good thing to include in this article. --Nogburt (talk) 05:21, 11 September 2016 (UTC)

While neutrality issues may have their importance, I find this article lacking information on real-life performance of CRTs when compared to flat panels (LCDs, etc). Anybody with reasonably healthy eyes and no bias, will instantly recognize the terrible color rendition, edge rendition and moving image rendition of most "modern" displays when the signal does not correspond to the native resolution of those modern displays, for example, when viewing a standard ("low definition") cable signal or DVD on an LCD with higher rated resolution: the CRT image will be slightly blurred perhaps, but EVERY OTHER aspect of the perceived quality of the image will still be much better in the old and relegated CRT. The fact that modern displays require a different from "standard def" signals is seldom recognized. That is the reason why I keep my old Toshiba 32" CRT TV bought in 1997: it simply looks much better than ANY modern display when looking standard definition cable-TV or DVDs, except perhaps that the Channel logotype is slightly less defined in the CRT (everything else in the image is MUCH better!). Amclaussen. — Preceding unsigned comment added by (talk) 17:10, 11 January 2017 (UTC)