Back in the 80's as a test I set an 8k eprom in direct sunlight everyday to see how much it could take. If I recall correctly it took about 5 days before it failed a checksum test. Different eproms will have different sensitivities but I never meet one in all the years that complained about a few hours under room lighting. Just not enough UV there.
Sure, but bear in mind the EPROM in the keyboard was probably programmed back in 1986 or so. So over 26+ years the amount of stored charge would have deteriorated, meaning there is more chance of UV/sunlight damaging the stored data now.
