Oscilloscope 'fluorescence' - Page 1
Forum section: electronics / beginners

author: peterllbr
author_rank: Newbie
timestamp: May 26, 2014, 07:20:33 am
content: Hi guys, long time David fan and super electronics noob here.I have a question that has been bugging me.I brought a tektronix 2232 scope some time ago, it works great.But, by night, when I am in my bed I can see the screen scope in the darkness,it's some kind of 'fluorescence' thing.The scope is not plugged.is this a normal behavior? .. or the scope is emitting something?I work all day near to the scope, due this I am a bit worried.... sorry if this is the stupid question of the year.Thanks guys.

author: Skimask
author_rank: Super Contributor
timestamp: May 26, 2014, 07:22:51 am
content: http://en.wikipedia.org/wiki/Phosphorescence

author: ErikTheNorwegian
author_rank: Frequent Contributor
timestamp: May 26, 2014, 07:38:34 am
content: Its the Scope ghost that haunts in the night.. dont sleep,in the same room as a scope!

author: peterllbr
author_rank: Newbie
timestamp: May 26, 2014, 07:48:52 am
content: Quote from: ErikTheNorwegian on May 26, 2014, 07:38:34 am; )OK, the phosphorescent screen is emitting the radiation it absorbs.It emits for weeks after a normal session, just saying.Thanks guys, normal ghost behavior i conclude.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 26, 2014, 08:57:47 am
content: Strange, my 475 only glows for seconds, minutes at best. Wouldn't think the 2232 would have a terrifically different phosphor.But yes, CRT phosphors do indeed "charge up" from room lighting.Tim

author: peterllbr
author_rank: Newbie
timestamp: May 26, 2014, 09:24:01 am
content: Quote from: T3sl4co1l on May 26, 2014, 08:57:47 amIt's a really weak glow, just visible in total darkness.And yes, I think the screen absorb the sun light to keep my tan in shape by night ; )

author: vk6zgo
author_rank: Super Contributor
timestamp: May 26, 2014, 09:44:58 am
content: Quote from: peterllbr on May 26, 2014, 07:20:33 amThe phosphor can absorb ambient light & re-emit it during the night.It is quite harmless,as you absorb the same amount from the light source during the day as the screen does,with no ill effects.

author: dentaku
author_rank: Frequent Contributor
timestamp: May 26, 2014, 10:51:14 am
content: Interesting.My Hameg HM605 only glows for a few minutes.

author: edy
author_rank: Super Contributor
timestamp: May 26, 2014, 01:56:48 pm
content: I have a couple of CRO's and never noticed anything but I will have to look at them now. I wonder if this has anything to do with thin grounding wires that run along the inside of the phosphor screen, to dissipate any remaining electrostatic charge?One of the games we used to play as a KID when we had the old Cathode-Ray TV sets (in the good old days) was rub our head on the nice fleecy blanket or rub our feet across the carpet and touch the TV when the lights were PITCH BLACK and we could draw on the screen with our fingers!You can impress your children today by getting a Fluorescent TUBE lamp, have them hold it, and on a nice DRY WINTER night when humidity is almost nothing and static build up is high, rub the heads on the pillow or blanket while they touch the tube and it will GLOW!

author: ResR
author_rank: Regular Contributor
timestamp: May 26, 2014, 02:14:30 pm
content: I have seen same thing with the soviet black and white TV with vacuum tube technology, it absorbed light from the sun and glowed barely visible in dark, note the TV wasn't plugged in for months. It's harmless to you and to the oscilloscope, "glow in the dark" stickers do the same thing only little bit brighter for a few minutes.

author: c4757p
author_rank: Super Contributor
timestamp: May 26, 2014, 02:21:40 pm
content: Quote from: T3sl4co1l on May 26, 2014, 08:57:47 amQuote from: dentaku on May 26, 2014, 10:51:14 amHow dark is the room? My house is away from any sort of city lighting, and at night, with the lights off and the moon hidden, there is close to zero light from anything at all. After ten or twenty minutes of waiting for my eyes to adjust, I can catch a very, very faint glow from both of my analog scopes for at least a few hours. Eventhe glow from the moonhides this, though.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: May 26, 2014, 02:28:31 pm
content: Now imagine many scope owners worldwide going to the toilet with their scope to see if it glows in the dark.

author: Thilo78
author_rank: Regular Contributor
timestamp: May 26, 2014, 05:09:04 pm
content: Quote from: T3sl4co1l on May 26, 2014, 08:57:47 amAnd from normal use, as well. That effect always backstabbed me with my small TV, when I was a kid.When it was bedtime, I wasn't allowed to watch TV, but of course did. My dad would eventually take a glimpse in the room, see the afterglow on the CRT and tell me off about being up late, watching TV.Quote from: KedasProbe on May 26, 2014, 02:28:31 pmHow did you know?!

author: edpalmer42
author_rank: Super Contributor
timestamp: May 26, 2014, 05:39:49 pm
content: A lifetime ago, when I was studying EE at university, it was common to work on Saturdays on labs and experiments. One Saturday, in the middle of winter, I happened to be the last person out of the lab so I turned off the lights on my way out. It was late and it was dark. Out of the corner of my eye I saw something lit up. I looked back into the lab to see about 30 old Tektronix scopes all lined up against the wall staring at me with their one spooky green eye!Ed

author: DonRon
author_rank: Regular Contributor
timestamp: May 26, 2014, 05:44:39 pm
content: I can see same thing on my Hameg HM1008 - even if I did not use it for several days. But the glow is very weak.Cheers,Ronald

author: Zero999
author_rank: Super Contributor
timestamp: May 26, 2014, 06:39:31 pm
content: I have a couple of old CRT oscilloscopes in my bedroom. They haven't been used for years and they still glow in the dark. It's the natural light exciting the phosphor, just like glow in the dark toys.Only CRTs do this. Modern oscilloscopes which have a TFT display don't glow.

author: peterllbr
author_rank: Newbie
timestamp: May 27, 2014, 08:16:26 am
content: Thanks to all, very informative and funny thread.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 27, 2014, 08:38:14 am
content: Ah, absolute darkness, dark adjusted eyes? Yeah, it's probably visible for a few hours on that scale. Don't know that I ever observed my scopes that dark before.Tim

author: marshallh
author_rank: Unknown
timestamp: May 27, 2014, 06:11:56 pm
content: Yes, many EL strips and CCFL panels do this as well for hours after they're shut off

author: David Hess
author_rank: Super Contributor
timestamp: June 01, 2014, 02:14:02 am
content: My 22xx and 24xx series Tektronix oscilloscopes do the same thing. The glow is visible for hours at least and occurs even if the oscilloscope has not been used. Just room lighting is enough to excite the CRT phosphor.