Re: I've got an Autogated question.....
What you're referring to is BSP or Bright Source Protection and, yes, your tube has it.
From the milspec ( yes, I know your NE isn't Milspec, but it will conform pretty much to this ).
"5. Bright source protection. With operating potential applied, the assembly shall not be damaged (see 3.6.9) when subjected to an input illumination of not less than 50 milli-lumens concentrated on the photocathode within an area no greater than one square millimeter for a time interval not less than one minute. There shall be no discernible damage (see 3.6.9) after a non-operating period of not more than 24 hours"
That's from the latest Omni VIII Milspec and yours would be closer to Omni VI or VII probably, however the function is much the same... Bright light, same spot, one minute, should be no damage.
You could calculate how bright and how far away, but here's the general idea... If the light itself is directly visible, look at the halo. A single level halo ( normal size ) means the light isn't too bright. A double sized or enlarged halo means it's too bright.
But for the sake of maths, lets assume that you want a real world example. 1 mm square = 4 degrees. That would be a porch light equally diffused over 60cm ( two feet by two feet ) producing 2000 Lumens of light, which is pretty bright - say 100W at 120v.
Now, under those conditions, if you were 10m away, your photocathode would get 1 millilumen of light - not much - well under the 50 in the milspec.
But in the real world, lights are smaller than 2 feet by 2 feet.
Let's assume it's a 1 foot by 1 foot diffuser. Well, that would increase the intensity at the photocathode by a factor of 4. So now it's the same strength of light over a smaller area- the equivalent of 4 millilumens over the full 1mmsquare area.
But people don't use diffusers, so let's assume it's just a bulb. That's about a quarter of the size again ( 3" x 3" ) so the increase in energy at the photocathode would be around 64 millilumens equivalent - WAY too bright.
So that gives you an idea. Don't get closer than, say, 20m ( or 20 yards, these are rough figures ) to a light while looking right at it for more than a minute, because you're out of spec.
I'm going to take a wild guess and assume you don't do that - that the lights are 100 yards or more away. So that's fine. For short periods of time. And no damage should result from your activities.
HOWEVER, the tube life is based on how much light it sees. So while it won't damage the tube, it will shorten the tube life. Considerably.
Finally, practical sense can help with the rest. If you're in a military situation, you may need to look into bright areas for some time. Since you're not, just look around once in a while. Make sure the spots aren't still in your NV ( eg, don't put it down while looking at a light ) - learn the "turn it on in a sock drawer wrapped in tinfoil" trick and if you do get burn in, get an idea how long it takes to get it out.
Because if you're not getting burn in or if the problem goes away after a few minutes, then you're not going to damage the tube.
Hope this helps -
Regards
David
But, I have to look their way from time to time.....so my question is how much light does it take to damage a tube???
