On Fri, 17 Aug 2012 16:40:00 -0700 (PDT),
wrote:

I used only sunlight (Phoenix, AZ, 32N latitute, sky probably 90% clear),
and for EPROMS written with all 0s, over 90% of the bits would erase
in a day, 100% in 2 days, so I'd erase for 3-5 days.

In the late 1960's, I was working on a nifty new product that included
some of the first EPROMs. The prototype was done and the boss
declared that it was time to take a proper photograph for the product
release, manuals, promos, literature, etc. After the photographers
with their bright lights were done, I couldn't make it work. I
eventually determined that all the EPROMs had at least been partially
erased. My guess is about an hour under the very bright lights. I
didn't see the lights but suspect they could have been arc lamps as
incandescent lamps doesn't have enough UV content to erase EPROMs.
Installing a spare set of EPROMS got it working again. After that
experience, I made it a habit of putting labels over the EPROM window.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558