Sickness from Monochrome CRTs? - Page 1
Forum section: electronics / general

author: JPortici
author_rank: Super Contributor
timestamp: May 11, 2016, 05:09:35 pm
content: I don't know.I remember feeling this since i was very young and one of the computers in the local library was a b/w crt with a "radiation" protector.. and when i removed the protector i would start to get a little dizzy, light headache, just like when you have a little fever. This would stop some moments after i would switch off the screen.Same happened with every monochrome i ever used.. Old computers, analog oscilloscopes, CRT screens (was doing the CV mod to a vecrex... BEAUTY!) as soon as i switch them on that ache comes.Is it only me? Am i allergic to CRTs?

author: stmdude
author_rank: Frequent Contributor
timestamp: May 11, 2016, 05:30:36 pm
content: You might be "allergic" to rapidly blinking lights...If I recall correctly, the radiation-protector reduced the overall brightness of the display by quite a bit, so the amount of flashing wasn't as much for your eyes+brain to handle.But, it's all guesswork..However, the amount of x-ray radiation from CRTs wasn't as bad as people made it out to be. The "worst" CRTs emitted about 0.5mR/hour (milli-roentgens).The amount of x-rays you get from just existing on the planet earth is about 100mR/year.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: May 11, 2016, 05:44:33 pm
content: How good is your hearing? I can hear the hum from CRTs and it gets annoying, maybe you're not concious of it so it manifests as nausea?

author: helius
author_rank: Super Contributor
timestamp: May 11, 2016, 05:53:07 pm
content: I guess the "radiation protector" was a glare reducing filter. They are made of very fine polyester mesh and would snap in to the bezels of some older CRTs. Very annoying to have to wash them after they got filled up with dust.X-ray protection is always integral to the tube itself, by using lead and barium doped glass. It works quite well to limit exposure to the user: X-ray dose is higher at the back of the display than the front as a result of the shielding. Anyway, I don't believe that humans can feel any effects from this level of ionizing radiation, which is one reason it needs to be closely regulated.The actual frequency of oscillations of high-resolution* CRTs are outside the range of hearing, but people can hear subharmonics of them, especially if there are failing components in the horizontal circuit. I wouldn't think that electrostatic deflected oscilloscopes would be audible at all.* edited because I forgot that SDTV has an oscillation at ~16 kHz. This can be audible if not masked by other sounds.

author: BobsURuncle
author_rank: Regular Contributor
timestamp: May 11, 2016, 05:54:00 pm
content: What you call a radiation protector is probably an anti-glare and implosion protection - actually you can't remove IP easily. The reduced glare may be one reason it is less bothersome. And brightness will be less, as stmdude mentioned, so flicker will be less evident. Another thing could be electrostatics, which can make your skin uncomfortable and these panels often had anti-static protection as well.

author: JPortici
author_rank: Super Contributor
timestamp: May 11, 2016, 07:48:59 pm
content: i think so, that it what it was called back then and in fact i put that into quotesThe sensation i feel i feel it with monochrome only, never felt it with a color tv or screen, unless i stood in front of it for hours a day, of courseAnd of course i feel that from every angle i'm standing in respect of the crt. I always thought it was in some way x-ray relatedYes i can hear the CRT hum, even if being a musician probably destroyed my hearing from 13k and up i am pretty sensible in the low range, but that doesn't bother me at all. my house is next to a factory that hums all night long but that relaxes me, i got used to that over the time (i find it much harder to sleep with silence)

author: ez24
author_rank: Super Contributor
timestamp: May 11, 2016, 07:54:27 pm
content: If you start to have weird health issues, get your thyroid checked.

author: stmdude
author_rank: Frequent Contributor
timestamp: May 11, 2016, 07:56:28 pm
content: Quote from: JPortici on May 11, 2016, 07:48:59 pmProbably not. Humans can't "feel" X-Rays.I'm sure you've had an X-Ray taken at a hospital at some point. When that X-Ray was taken, you got the equivalent dose of 200 hours in front of a CRT in a fraction of a second. Did you feel the X-Ray being taken?

author: JPortici
author_rank: Super Contributor
timestamp: May 11, 2016, 08:05:25 pm
content: Quote from: stmdude on May 11, 2016, 07:56:28 pmExcellent pointI should mention that i don't believe it for a second that i some kind of superhuman sensibility. What i meant is that i think that there is a correlation with me being near the tubeStrange.. or not, nobody else seems to be affected. I would have thought/hoped that somebody else would have showed up by now

author: Maxlor
author_rank: Frequent Contributor
timestamp: May 11, 2016, 09:23:23 pm
content: Do you get the effects when you're merely close to a CRT, or do you have to be looking at it too? If it's only when looking, my guess is you're sensitive to flicker. Might be that you think color CRTs is better because they're more modern, and were often running at more than just 50 or 60Hz to avoid just those effects.Personally, I can see flicker below approximately 75Hz (or could many years ago, when my computer still used a CRT), and find it rather irritating. Low frequency CRTs didn't give me headaches or anything though, because that irritation usually made me stop using them or increase the refresh rate if I could as soon as possible. I'm very grateful for modern LCD screens (and wary of buying one with PWM controlled backlight.)

author: JPortici
author_rank: Super Contributor
timestamp: May 11, 2016, 09:35:06 pm
content: I am sensible to flickering (3d movies sickens me. also for this reason) but it's not the case. Usually i just have to be near it (funny, my "new" 7704 is not giving me aches so far, the vectrex i was repairing the other day just had to be switched on. i didn't even have to be in front of it)

author: helius
author_rank: Super Contributor
timestamp: May 11, 2016, 10:29:52 pm
content: It could be ultrasonic in nature.

author: station240
author_rank: Unknown
timestamp: May 11, 2016, 11:04:40 pm
content: The other thing to consider is Interleaving (scan lines). The filter obscures this, but without it, you get a slight moving image. If the mind is able to observe the interleaving, then it could create motion sickness.

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: May 12, 2016, 12:18:39 am
content: Tube face plates were quite thick and was made from lead glass which helped with absorbing most of the x-rays.So any symptoms you experienced may be optical related. Flickering is one. Your eyes trying to focus on images that are not particularly sharp on a CRT can also cause some strain.

author: Hydrawerk
author_rank: Super Contributor
timestamp: May 12, 2016, 12:24:59 am
content: Quote from: Mechanical Menace on May 11, 2016, 05:44:33 pmMe too. I do not like CRT TVs and I am glad that they are gone and will not return.

author: BobsURuncle
author_rank: Regular Contributor
timestamp: May 12, 2016, 12:32:37 am
content: Quote from: JPortici on May 11, 2016, 09:35:06 pmBeing closer increases visibility of flicker. Brighter and a wider field of view makes it more apparent.Newer CRTs run at higher refresh rates than early models. Interlaced monitors and TVs refreshed a frame at 30Hz. Also I think the time constant on monochrome phosphors was generally faster. The warmer the color the less efficient and if memory serves slower decay times which reduces flicker. It was always a compromise between phosphor efficiency, flicker, burn-in and color preference in monochrome tubes.It could all be in your head. You had a bad childhood experience with the library version and have come to associate it with all CRTs - refueled by misinformation about X--rays.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 12, 2016, 12:42:56 am
content: While the corner frequency of human hearing is around 15kHz, it does not mean you cannot hear higher frequencies. When I was in my twenties I found ultrasonic motion detection systems used in burglar detection systems quite annoying. Since most people couldn't hear them they were left on during store operation hours. I believe they operated at about 22kHz. I did informal hearing tests on myself and could clearly hear sounds up to 22 or 23 kHz if they were loud enough. It was a real relief when age and other assaults on my hearing made most sounds about 10 kHz inaudible.Sound might be the culprit on many of the displays, but oscilloscopes don't consistently have sound sources in these ranges and the OP mentioned oscilloscopes as one of the triggers for his problem. It seems more likely that flicker sensitivity is the issue. Flicker is an issue anywhere in the visual field so even indirect viewing of reflections or scattered light from a flickering light source can trigger the issues.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: May 12, 2016, 01:00:28 am
content: I would sometimes get a little nauseous from looking at very high contrast displays. I could get text to do this to me on my TFT monitors when I first switched to them from CRT. I imagine the monochrome CRT pixels were much crisper on the edges than those on a color CRT; maybe it was the same kind of thing?

author: KE5FX
author_rank: Super Contributor
timestamp: May 12, 2016, 01:15:22 am
content: Quote from: ez24 on May 11, 2016, 07:54:27 pmAlso check the building for CO leaks.

author: helius
author_rank: Super Contributor
timestamp: May 12, 2016, 01:54:55 am
content: Quote from: CatalinaWOW on May 12, 2016, 12:42:56 amThis is a good point. The sensitivity to flicker is higher in the periphery of the eye than in the fovea, as the rod cells have a faster response compared to cones.

author: JPortici
author_rank: Super Contributor
timestamp: May 12, 2016, 06:14:19 am
content: this makes perfect sense but it still doesn't address why it happens also when i am not looking at the screen but the crts is only switched on and i'm near itQuoteThe click and hiss they would make from time to time, awgod please no.

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 12, 2016, 08:13:36 am
content: Maybe the EHT section is producing ozone and you get nauseous from the smell. A bit of a long shot though.

author: tszaboo
author_rank: Super Contributor
timestamp: May 12, 2016, 08:23:48 am
content: Quote from: JPortici on May 11, 2016, 09:35:06 pmI hear power suuplies, CRT monitors etc. Even LED multiplexing can make me feel dizzy. I've fount the frequency of that actually quite high. Now a CRT might be 75 Hz.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: May 12, 2016, 09:23:53 am
content: TL;DR:It's a) nothing to worry aboutb) likely a psychosomantic effect (or more accurately a nocebo effect)c) possibly a sensitivity to flickering lights (though this is less likely its by no means impossible!)Of the available options, this is most likely a psychosomantic effect: if you have a monitor that causes this effect nearby, get a second person to assists you and perform a blind test.Blindfold yourself, turn your back to the screen - your partner will then turn it on or leave it off - randomly decided by flipping a coin (the state of the monitor must be unknown to you)If you can hear the hum from the CRT (as I can) you'll also need ear protection (try earplugs and ear defenders - or even just stick your finger in your ears)After five minutes, state whether you are feeling nauseous - and then remove the protection and observe whether the monitor was actually on.Repeat this process say, 10 times (the more times the better, but this routine will get boring quickly!) and observe the results:If you felt nauseous and it was on - this is a positive - if you felt nauseous and it was off, a false positive. The opposite applies to negatives.If you had roughly equal numbers of positives and false positives (i.e if you were "right" 50% of the time (say, +/-5% for such a small sample size) - then you can be reasonably assured that there is no correlation between the monitor being on or off and you feeling nauseous - which suggests that its psychosomatic in origin - a type of nocebo effect.The problem comes if you don't get a roughly 50% positive rate - supposing you were "right" 75% of the time: this may not actually indicate that the monitor is causing it - it may simply be that the method is flawed in that you were somehow aware of the state of the monitor. It also raises the question that if you simply did feel nauseous when the monitor was on, why didn't it happen all the time?Finally, if you got a >95% (+/-5%) positive rate we can be almost certain that the monitor is the cause of the nausea.I know you can't be bothered actually doing this, but I must admit I'm curious now!

author: JPortici
author_rank: Super Contributor
timestamp: May 12, 2016, 10:50:40 am
content: Me tooi am relatively confident this is just my immagination but it would be nice to perform a blind testi'll think about it

author: tszaboo
author_rank: Super Contributor
timestamp: May 12, 2016, 11:26:33 am
content: Quote from: JPortici on May 12, 2016, 10:50:40 amLike, you dont look at the monitor, to know if looking at the monitor makes you sick?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 12, 2016, 02:25:54 pm
content: The blind test, as defined, can only prove that some unknown factor about the monitor is causing the symptoms. That is: If you are blindfolded and earmuffed you have eliminated two of the possible actual physical inputs.There are other possibilities. Let's say you run a test blindfolded, but with your ears able to hear and get a positive result. It may be a physiological response to the sound, but it could also be a conditioned response. Some monitor that you owned once may have given you flicker problems, and also had an audio tone. You may now be conditioned to have the physical response to flicker whenever you hear the sound. It requires more expertise than I have to suggest what to do if something like that is the case.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: May 12, 2016, 02:57:01 pm
content: QuoteIndeed! It will only give an idea as to if the monitor or the mind is the causative agent: it will not tell uswhyin either case.The pivotal point is that the test subject is entirely unaware of the state the monitor is in (as I said, I can hear them whine for instance!).In an ideal world the test would be double blind in that neither the testee nor the testor would know the state of the monitor during the test - but by this point you're putting way to much effort into it

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 13, 2016, 01:21:53 am
content: Quote from: cprobertson1 on May 12, 2016, 02:57:01 pmAfter this test you will not know if it is the monitor or the mind. If the effects are physiological, not psychological, and the mechanism involves the ears and/or the eyes this test will give a null response. Only if you get a positive response will you know more, and what you will know is that the monitor is causative through some mechanism other than sight or sound, or that the test operator is conveying information. If you get no response you can be fairly confident that the operator is conveying no information, and that no mechanism other than sight and sound is involved. But in either case you have no information on whether the effect is real or psychosomatic.

author: Raj
author_rank: Frequent Contributor
timestamp: May 13, 2016, 01:29:30 pm
content: that's just it?I am able to see the screen getting scanned also the ultrasound hum is very audible to me.Though I don't get sick from them, I do get irritated