LED Enlarger Bulb?

[That Guy]

Anyone ever thought of using an LED bulb for their enlarger? I was web-surfing tonight and came across this link for an LED bulb that has the same temperature rating as the PH140 bulbs for my Beseler. It's 50 bucks, but should last forever. I would think there might be a slight problem with the light being even across the frame. Whacha all think?

Chris

 

[MartinP]

They have been used for years in aftermarket, and homemade, products for diffusion enlargers, ever since extra-bright LEDs became available. There have also been variable-contrast heads made. A straight plugin replacement would have to have the same size and shape for existing heads if you were going to swap it in there, and be much more powerful too.

Another solution, as used in cold-cathode heads, is to have an always-on light-source with a shutter of some sort, so maybe a custom head with a larger fluorescent could be made - but there would be colour temperature problems as those lamps are do not have a continuous spectrum output.

In the discrete-LED based heads the older the design was then the more LEDs were used, due to brightness and evenness problems, but I suppose that now it should be possible for someone to come up with a very simple design - or it would if there was any r&d left in the enlarger business, as most of the original manufacturers have gone broke or diversified. 🙁

 

[Bryce]

My Beseler (23c with condenser head) holds its bulb sideways. Also, the area around the smallish bulb is pretty tight. So for those reasons I don't think the bulb you've shown would work in mine without alterations.
There would be improvements though- less heat has to be a good thing! And unless you're printing on color paper, it seems unlikely there would be any difference in contrast or the like.
Stupid questions, though- do LED's have a startup period where their illumination is not the same as after running awhile? What is their longevity like being used intermittently, bearing in mind that to work on mains power they must have a built in transformer and rectifier?
If anyone actually tries this, please post your experiences!

 

[rxmd]

Stupid questions, though- do LED's have a startup period where their illumination is not the same as after running awhile? What is their longevity like being used intermittently...

LEDs do not have a startup period, and their longevity isn't really affected by being used intermittently. LEDs have much better longevity than any other light source you could use in your enlarger. They're pretty much perfect for use in an enlarger. If you use red, green and blue ones you get instant splitgrade and safelight capabilities.

bearing in mind that to work on mains power they must have a built in transformer and rectifier?

Actually technically you need neither. The LED is a rectifier in itself, and you can do without the transformer if you dimension your resistor accordingly. Of course using the LED as a rectifier is a bit crude; you could at least use two LEDs in opposite directions to get 1 stop of brightness at no cost except the second LED.

Philipp

 

[That Guy]

I have a Printmaker 67 that I was thinking of using this in. Its a condenser so having even light would be the hard part. Martin, I hadn't considered comparing the lumens of the bulb, just the color temperature. The bulb at the weblink I posted has the correct temp, but only a 30W equivalence. I suppose it would still work, but the exposure times might be closer to a diffusion head. Bryce, my Printmaker has a vertical alignment and will fit a standard four inch bulb and a normal household bulb does fit. Makes me think I could actually make this work. If I give it a go, I'll let you all know.