whit@milton.acs.washington.edu (John Whitmore) (04/10/90)
I've been reading this thread for a while, and it seems to need more meat, so I'll put my two cents in. Mercury vapor has two strong UV lines, one at 2536 Angstroms (called "short wave UV") and another (a set, actually) at 3663 Angstroms (called "long wave UV"). Typical "black light" bulbs are Mercury vapor lamps without phosphors (as fluorescent bulbs are Mercury vapor lamps with phosphors), with a filter (or filter glass) to reduce the "short wave" emissions. Short wave UV is what the EPROM manufacturers specify to erase their EPROMs; it also destroys any living tissue (like corneas and germs). A cheap eraser can be made from a high pressure mercury lamp (like those used for yard illumination) by simply cutting off the outer filter glass envelope (the inner envelope is quartz and does no filtering). Cost: circa $35. Safety: nil. One can erase EPROMs with a "black light" bulb at CLOSE range for LONG times (go to dinner, maybe it'll be erased when you get back). Cost: $35 and (on a per-use basis) a couple of hours. Safety: adequate. This depends, I believe, on the leakage past the filter, probably NOT on the longwave light that was supposed to be produced. I've done it, so I know it works. Any fluorescent tube with "BL" suffix is a long-wave black light type bulb. If you are in any doubt as to whether shortwave or longwave UV is being produced by a given bulb, turn it on for a few minutes, and sniff. If you smell ozone, it's shortwave UV. Ozone, by the way, is about twice as toxic as carbon monoxide, so don't use a BIG lamp if a small one will do... Your skin is good protection against long wave UV. Short wave UV can do severe damage, however; limit your exposure by using a suitable enclosure (many glasses and some plastics are reliably opaque in this part of the spectrum). Commercial erasers are usually interlocked so the enclosure must be closed before the lamp can be turned on. I am known for my brilliance, John Whitmore by those who do not know me well.