Light source power and distance ...

[CG]

Why not just use a prewired screw in LED bulb assembly? No wiring. No transforming voltages, no soldering, no resistors... Just hook up your timer to a screw in socket and go.

I happen to use these: http://www.superbrightleds.com/cgi-b...cs/E27-W24.htm (the green and UV bulbs) but there must be a bunch of companies making similar products by now. I bounce a green and a blue/UV LED bulb off the ceiling to even out the light and bring the exposure time up a bit. They are pretty bright as seen by the paper even though to the eye they don't seem all that bright. I painted a small patch on the ceiling dark to help lengthen exposures. Each bulb is plugged into a separate timer. It works pretty well. They make white bulbs too.

[aduncanson]

Conventional 60 Watt bulbs put out about 520 lumens. They are nearly omnidirectional. If the bulb is 170cm distant from the paper, that would make .0015 lumens/cm^2. However you need to estimate what fraction of that 520 lumens is actinic, or effective at exposing photographic paper.

I use a 50 Watt Halogen reflector flood (with a higher color temp than a conventional bulb) at about 170cm. Based on representative specifications (and a guess about its radiation pattern), I estimate that it makes about .006 total lumens/cm^2 at the paper. I get exposure times on the order of 15 seconds on Lodima, which is much less sensitive and more specifically blue/UV sensitive, than most enlarging papers. I find my set up much too fast for contact printing on enlarging paper, but I would not abide an exposure time shorter than 4 or 5 seconds.

[Karmelo Martin]

Why not just use a prewired screw in LED bulb assembly? No wiring. No transforming voltages, no soldering, no resistors... Just hook up your timer to a screw in socket and go.

I happen to use these: http://www.superbrightleds.com/cgi-b...cs/E27-W24.htm (the green and UV bulbs) but there must be a bunch of companies making similar products by now. I bounce a green and a blue/UV LED bulb off the ceiling to even out the light and bring the exposure time up a bit. They are pretty bright as seen by the paper even though to the eye they don't seem all that bright. I painted a small patch on the ceiling dark to help lengthen exposures. Each bulb is plugged into a separate timer. It works pretty well. They make white bulbs too.

Mmmhh... Very interesting. So you are getting exposure times of 15 secs (On Lodima) with just two of these bulbs hang on the ceiling?

OK. I think that's all I need for the moment...

thanks a lot for all of your replies guys,
Carmelo

[mhulsman]

Carmelo,

Look at this article http://www.apug.org/forums/forum43/5...roic-leds.html

30 x Luxeon III leds in a 10 x 10 light head will give about 2750 Watt of light.
That will all fit in a Durst L184/301 head.