Oriental graded RC paper super sensitive to safelight exposure

Like.
All my life I improvised.

For scientific details about beer bottle { beer safety and ... possible foggy vision } spectrum read this:
http://www.edenfoods.com/articles/view.php?articles_id=181

Beer bottle seems to have ~600 nm peak but quite large spectrum.

LE
Why bother with batteries ? .. why you don't use universal 5V ( 2.5 W ) aka USB socket ? computer or charger.
Or cheap "night light" directly in mains socket with a bottle over it.