enlarging light source

[Colin Seaman]

Was wondering if anyone had used a neon light as a cold light source for b&w pri nting? I know that Aristo uses a mercury vapour lamp in their cold light sources , but wanted to know how neon affects b&w papers? thanks

[Tony Brent]

True neon (orange glow) wont expose paper at all. In fact, it's probably a fairly decent safelight. Mercury vapor lamps emit a high percentage of high energy UV and near-UV which is very effective in exposing photo materials. There used to be a line of contact printers used in the military photo labs for contact printing 9 inch aerial film that used a bank of Argon (blue glow) lamps in a grid containing maybe 25 lamps that could be switched on or off for local dodging. You cant mistake the machine -- they need four people to lift them.

[Colin Seaman]

this particular neon lamp is very blue, much colder looking than say a daylight fluoresent tube. I have no idea what level of UV the lamp emits if any.

[Doremus Scudder]

Flourescent tubes use a number of different noble gasses wihich emit light when an electric current is passed through them. As mentioned above, neon gives off a n orange red, argon gives a green light, etc., etc. The actual color of light yo u get depends on the flourescent coating of the tube you have. A fine coat of fl ourescent powder is applied to the inside of the tube which absorbs light of one color and emits light of another. Manufacturers mix and match flourescent mater ials to come up with many different combinations for different purposes and tast es. These tubes do not emit a continuous spectrum so a color temperature meter w ill not give you any usefull information. You could write the manufacturer, of f ind someone with the necessary diffraction measuring equipment, or just experime n. Of course, if you ever change tubes, the characterstics will probably be diff erent. Since most B&W emulsions can be exposed with blue and blue-green light, a ny light source with these characteristics will work. Time and, with variable co ntrast papers, filtration will vary according to actual spectral composition and intensity. Regards, ;^D>