Light Reactive Chemical/ink

[Brightidea]

Hi, I'm currently in the process of designing a product. It needs to work like invisible ink, but instead of reacting to UV light, I need it to show up when exposed to a normal bright light source. For instance if this clear ink was used on a piece of paper, then photocopied, it would show up on the print. Although the ink on the original piece of paper would remain invisible. I'm not sure if any chemicals used during the process of film developing would be useful? The chemical must be safe to use and be non permanent if used on glass. Any comments or suggestions would be greatly appreciated.

Thanks

Edited July 5, 2008 by Brightidea
more info

[alwynj48]

Hi,

 

Sounds like you want something that is no linear. Meaning at low light intensites its white or transparent and at high intensites it absorbs light so its black or at least colored. The obvous problem is if it's tranparent or white its not absorbing any light so it can't react to it. So it must have some absorbtion to start with meaning it can not be totally invisible.

 

Here is wiki link on photochromics http://en.wikipedia.org/wiki/Photochromic_lens

 

It also shows that major effort has already been expended on it