>> Lots of things that appear "light blocking" to us in
>> the visible range are surprisingly transparent at other
>> wavelenths.  Black electrical tape is a good example.
>> It attenuates visible light heavily (else it wouldn't look
>> black), but doesn't do much at all for IR.
>
>What do you suggest I use to block the window with? I put
> two layers of electrical tape over the window, turned off
> the desk lights and it appears to be trying to work
> intermittently anyway.

Now you may understand why labels put on EPROM's are often foil labels. Also
if you check through the archives you will find that people have had
problems with the JW packages, and not having the window covered the device
works happily, but when they then program an OTP device they have a problem
because the light was clearing the RAM on power up, and they forgot to
initialise it in their program.

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