Red Green & Blue LED head from a stage light for enlarger light source.

[Steve Smith]

I have a friend who owns a Stage sound and lighting company (I work for him sometimes).

Recently, they have been using LED stage lights for the smaller venues. These look like a normal stage light but have an array of red, green and blue LEDs instead of a bulb.

Whilst the light output cannot match a traditional type with a 500 watt bulb, the light output is quite impressive.

He had a couple with a row of green LEDs not working, so when he got replacements, he gave me the the PCBs to play with. In each case it was just one LED not working so I repaired one with an LED from the other to give back to him as a spare.

The remaining one I will use for a 5x4 light source. The LEDs occupy a 6" diameter area so I can re configure it just for the 5x4" area.

These lights are very cheap now, so could easily be modified for enlarger use.

I am planning a variable mix (PWM) between blue and green with an all on full option for focusing.

Each colour draws about 300mA at 30 volts so there are no horrendous power supply issues.

(please excuse the crappy pictures. I just put it on the scanner).



Steve.

[Steve Smith]

A couple more:

[Daniel Ferri]

Steve,

I had the same thought about making a light source from LEDs.

The idea is exiting, as you can get a small light source, vastly reduced heat , and the beauty of RGB LEDs, effectively giving you a full colour head or variable contrast, Green/Blue, for us B/W printers.

The main restriction so far is the limited output, even if you use some 5W LEDs.

I am trying to modify a Durst 138s to give more light than the standard 75/110/300W enlarging bulbs.
The 300W bulb produce about 5000 lumens, and I am unable to find the equivalent, let alone brighter output from LEDs.

Metal halides bulbs do give great output; 125 or 150W = 12500Lumens!
But you are back to using multigrade filters.

High power fluorescent coiled bulbs exist up to 85W, equivalent 500W tungsten, not enough lumens and the bulbs are nearly 300mm long, and impossible to accommodate.

Would really welcome input/help from anyone who has tried.

Danny

[Struan Gray]

I am planning a variable mix (PWM) between blue and green with an all on full option for focusing.

'scuse me if I'm teaching you to suck eggs, but since the red LEDs are in-place already, you might want to have the option to have red-only light too. I'm not one of those who feels the need to focus with the paper in the easel, although some do, but I do like using a red filter to practice burns and dodges without having to remove the paper.

[Nicholas Lindan]

Beware cheap LED's:

electronicsweekly.com - Clock LEDs Simply Fade Away.php

[cnmne]

My experience is that the spectral output of common blue LEDs is too wide to obtain a grade 5 contrast. If you can live with grade 4 maximum, it might be fine.

[ic-racer]

My experience is that the spectral output of common blue LEDs is too wide to obtain a grade 5 contrast. If you can live with grade 4 maximum, it might be fine.

Thanks for the observation. If that is the case then a supplemental #5 filter may work. In fact the Durst CLS1840 Dichro head only went to 130M and came with a supplemental Magenta filter to go to 190M.

I'll follow this progress with interest.

It still seems to me that a timer circuit is easier to build (or buy) than a PWM dimmer. So, instead of setting blue and green intensity you set blue and green time. Basically it would could be split grade printing with the push of a single button.

[paul_c5x4]

My experience is that the spectral output of common blue LEDs is too wide to obtain a grade 5 contrast. If you can live with grade 4 maximum, it might be fine.

There are two, maybe three LEDs emitting blue light at slightly different wavelengths - It would help if there was a decent spectral response graph available so that "we" could say "to get grade N, you need wavelength Y" for the average VC paper.

It still seems to me that a timer circuit is easier to build (or buy) than a PWM dimmer. So, instead of setting blue and green intensity you set blue and green time. Basically it would could be split grade printing with the push of a single button.

But, but... You already have a computer in front of you. A little bit of code, and a few extra minutes with a soldering iron, and you have a high precision timer

[Steve Smith]

Beware cheap LED's:

But they were free. My favourite price!!

The company I work for manufactures printed silver cicuits on flexible polyester. We mount components with a conductive epoxy. Most of these components are LEDs. We have found that the white LEDs are extremely sensitive to static damage.

But, but... You already have a computer in front of you. A little bit of code, and a few extra minutes with a soldering iron, and you have a high precision timer

But, but... it's not in my darkroom!

It still seems to me that a timer circuit is easier to build (or buy) than a PWM dimmer.

Either individual green and blue times could be used or a PWM mix. The PWM circuit is fairly simple and I like the idea of a single control going from min. to max. contrast.

I used to build three phase input switch mode power supplies rated at several kW output so a little one for this is no problem!

Steve.

[ic-racer]

I used to build three phase input switch mode power supplies rated at several kW output so a little one for this is no problem!

Steve.

It would be great if you posted you schematic when you get that far.