Have you cleaned the mask and dial? Dial should NOT be cleaned w/water but with mineral spirits. Water will remove print. If it still isn't bright enough you could use a led lamp.
The mask looks like something that might shatter if I wasn't careful. The link above shows a shadowmeter mask. Is that the same thing as for the dial pointer?
Probably would just clean it w/oms too.
Is that a painting type product or something else?