Converting 5x7 Head to LED Technology?

[neil poulsen]

I have a Zone VI Type II 5x7 head that's no longer functioning. What with the state of LED technology these days, is it reasonable to think that I could myself convert this head using green and blue LED lights?

Assuming a stable voltage, how stable is LED lighting? Where could I order the components that would be needed? (Red and green LED bulbs.)

[metalsmith]

Watching, I have an Omega E in need of conversion!

[Eric Woodbury]

Neil, it can be done, but it is expensive if done correctly. LEDs are not voltage sensitive, but they are current sensitive. One electron gives one photon (excluding efficiency).

Personally, I use Cree Green and Royal Blue LEDs mounted on 'stars' from LEDsupply.com.

You need the LEDs, variable current sources, a heat sink (LEDs must be kind of temperature stable or their efficiency changes too much), and since the LEDs are such bright spots, you need to rethink diffusion between the source the lens. This may actually be the hardest problem of the lot. Even though LEDs are far brighter than what you've been using, diffusers are typically inefficient and absorb too much light.

I've designed many of these now and it's a pain. Most of them have 36 LEDs for an 8x10. And that's a lot of light. I have an efficiency diffuser design. Typically I turn the intensity down a few stops. Never used at full power (1A per LED). I've done one 'special' source for a friend that has 144 LEDs.

Fewer LEDs would provide plenty of light, but then the LEDs are further apart and diffusion becomes more difficult. Lots of tradeoffs. Proceed cautiously. Talk to the folks at LED supply. Perhaps they have some gear to simply the problem. They are a joy to use compared to any other light source I've used.

Good luck.

[neil poulsen]

Yes, it sounds like I'll need it. But, I think that account is overdrawn. Hmm.

Thanks for your response.

[Michael R]

I’m not sure how one gets around the heat issue without active cooling or at least a well designed metal enclosure. Heat dissipation would be the problem for me. But if you can do that, the rest of it is relatively (?) easy. I built a sensitometer with a continuous spectrum white LED strip wrapped around the inside of a box without too much trouble. It’s extremely bright, and uniformity comes mostly from the LEDs not pointing toward the exit. In other words they are indirect sources and the enclosure is functioning as a mixing/integrating box. This is the same principle as variable contrast/filtration diffusion light sources in enlargers. The best approach in my little opinion is to not make a LED light source (as I don’t really see the point) but best of luck anyhow.

[neil poulsen]

Interesting that these lights generate an excessive amount of heat. I thought they were supposed to be efficient???

[koraks]

Interesting that these lights generate an excessive amount of heat. I thought they were supposed to be efficient???

They are efficient. But if you have let's say 50W of LED power, you still have to dissipate 50W. The heat has to go somewhere.

The main difference in terms of thermal management between LEDs and regular bulbs is that the latter happily 'live' at many hundreds of degrees Celsius (the filament at least). The semiconductor junction of an LED needs to be kept below ca. 105C at all times.

Efficiency is higher for LED, thermal management is just different.

Heed Eric's comments about diffusor design. Strategically placed milky white plexiglass or even frosted/ground real glass work OK. They cost some light, but it's not excessive and given the efficiency of LEDs, you'll have plenty of exposure punch left over even at modest power levels.

If you google a bit, you'll find plenty of forum and blog posts reporting on LED conversions. They're all over the place conceptually, and in the end, they all do/did get the job done. Some are really simple, some are far more complex. For B&W, things can be kept very simple and still be very effective.

If you're 'good' with electronics, by all means go ahead. If you have trouble distinguishing voltage from current (and other basic knowledge & competence), I'd suggest getting in touch with an electronics enthusiast who's willing to work with/for you.

[neil poulsen]

Thank you for your thoughtful comments. My thinking was that, if energy's going into heat, then it's not going into light, and that lowers efficiency. But, I suspect that the wasted energy going heat using incandescent bulbs is just so grossly greater than with LED's, that by comparison, the latter is "efficient".

But practically speaking, efficiency isn't really relevant to the discussion. I was just making an off hand observation.

In fact, I'm interested only in black and white enlarging. I would need green and blue sources for variable contrast illumination. But even for the simpler case, I have a feeling that I might be a bit out of my depth. I have facility with electricity and have done quite a lot of wiring for this or that project; but, I have little facility with electronics.

[freesky1992]

https://www.largeformatphotography.i...D-light-source
This thread might help you and Im planning to build one too,this project looks very complete with an useful controller~

[Michael R]

Neil, why do you want to move from incandescent to LED?

Thank you for your thoughtful comments. My thinking was that, if energy's going into heat, then it's not going into light, and that lowers efficiency. But, I suspect that the wasted energy going heat using incandescent bulbs is just so grossly greater than with LED's, that by comparison, the latter is "efficient".

But practically speaking, efficiency isn't really relevant to the discussion. I was just making an off hand observation.

In fact, I'm interested only in black and white enlarging. I would need green and blue sources for variable contrast illumination. But even for the simpler case, I have a feeling that I might be a bit out of my depth. I have facility with electricity and have done quite a lot of wiring for this or that project; but, I have little facility with electronics.