Really? Good to know, however; I'm using one bought at Walmart. One you would use in your house in a lamp. It's frosted and has print. The printing on the bulb does show up, when the condenser [Those 2 big pieces of glass] below the light lamp housing, are removed, otherwise; I don't see any printing on the board that the paper sits on.
I guess I can google enlarger bulbs to see if I can grab one somewhere.
It can be interesting if you have a large, evenly toned area. Sky? with GE 25 Watt in it. :o)