Help converting cold light Graflarger to LED

[Tim Meisburger]

Well, I finally did it. This morning I accidentally connected my 120v Graflarger to the 220 mains and fried it. I pulled it apart, but it looks rather hopeless, and to replace the cold light head and starter is probably more cost than its worth.

So, I could probably hack up a holder for a couple of compact fluorescent bulbs or, it occurred to me, I could mount LEDs in the original housing. The compact florescent would give me two circular sources and might create round hot spots, but would be easy, while the LEDs could be mounted in a rectangular pattern, but I have never used them.

Any advice?

Also, can anyone point a spot meter at an enlarger light source and give me a reading? That will help me determine how much light I need.

[SMBooth]

Here a start
http://www.apug.org/forums/forum43/96720-converting-omega-5x7-e3-cold-light-head-leds-100-a.html

[Tim Meisburger]

Thank you. I saw that, and it convinced me its possible.

Best, Tim

[vinny]

[/QUOTE]
Also, can anyone point a spot meter at an enlarger light source and give me a reading? That will help me determine how much light I need.[/QUOTE]

No, it won't. You need an incident reading at a certain distance from the light source.

[Leigh]

Be careful of heat. Graflargers aren't very big. High-intensity LEDs can generate significant heat.

You'll probably need a heat sink or a baffled forced-air cooling arrangement.

- Leigh

[Tim Meisburger]

Thanks Vinny. I think if I could read the diffusion glass at a particular distance and match that with a new light source I would be in the ball park, but I may not need it now. I have been reading more and one article said an enlarger bulb is 150 watts. If that is correct then I would need about 15 watts of LED to match the light output.

Leigh, that's interesting. I know nothing about LEDs, but some things I read say they are cool, and others say they are warm. One article said they put out a tenth the heat of an incandescent bulb, but even a 15w bulb would be too hot for the cold light box from the graflarger, so I guess if I use LEDs I'll have to make a new box. I would have to do that with the compact fluorescent as well.

[Leigh]

Hi Tim,

LED technology has made great advances in the last few years.

Old-tech LEDs produced very little light, and dissipated very little power.

New-tech "high-intensity" LEDs produce much more light, and dissipate much more power.

You really need to consult the manufacturer's datasheet for the LED involved
and do a thermal analysis of the design to determine cooling requirements.

- Leigh

[jp]

I haven't done it yet, but I'd look at some LED light panels on ebay made for video. They are available in a variety of rectangular sizes, many of which should be fine for 4x5.

[Steve Smith]

Have another search around APUG. There are a couple of posts about my DeVere 54 conversion using the LED PCB from an LED stage light. If I find them myself, I will post the links.

EDIT: (links)

http://www.apug.org/forums/forum43/77095-i-now-own-large-format-enlarger-3.html

http://www.apug.org/forums/forum43/79848-results-led-enlarger-light-source.html

http://www.apug.org/forums/forum43/79848-results-led-enlarger-light-source.html

http://www.apug.org/forums/forum43/79213-led-enlarger-head-update.html

Steve.

[Tim Meisburger]

Thanks Steve. That is useful!

[Ari]

This article is from a forum member who rigged his MF Beseler to handle 4x5; in the process, he had to make a new, and larger, light source out of LEDs.
Instructions on making the head are halfway down the page:
http://www.deadbread.com/crumbs/23c.html

[cardiomac]

Let me add to the excellent advice you have gotten already.

I suggest you use Cree warm white XP-E or the XM-L EasyWhite LED's. You want many, medium brightness LED's, not few really bright LED's because you have limited space to diffuse the light. Get them pre-mounted on a star - they will be much easier to handle. Check out the LuxDrive series. The stars can be screwed or epoxied to the heat sink with thermal epoxy. A heat sink is critically important. LED's don't generate much heat but they are very intolerant of what heat they do generate. You want to keep the LED's less than 75 degrees centigrade. Above that the life span is greatly reduced. Also, LED light output is inversely proportional to temperature, in some cases to a significant degree. The trick is to keep the working temperature stable. This means a large thermal mass and a large heat sink. Prewarming the LED's for a few minutes before making your first exposure is good practice. Use a constant current driver - 700mA is the most common. The voltage varies with how many LED's you are driving. Just make sure the total forward voltage drop of your LED's in series is within the range of the driver you have chosen. Recom makes good drivers. Remember, the majority of the power output of the driver will end up as heat so plan your heat sinks accordingly.

Overall, the best single source for components is DigiKey. Also, ReefLEDLights has good values on heatsinks. Good luck.

[Tim Meisburger]

Thanks guys for all this advice. Truthfully, although I'm a fair carpenter, my knowledge of electricity doesn't extend much beyond wiring switches and outlets. We don't have any radio shack here in Thailand, but I did find little shop selling 1.5w leds and I bought 50. Although they didn't speak much English, I was able to gather that they should be wired in parallel (which makes sense) and that if I added a resistor to each positive pole (the long wire) I would change the voltage required from 3 volts to 12 volts. Why that was preferable I couldn't get, but I went ahead and bought fifty resistors as well. Today I was talking to my landlord, who understands electronics, and he essentially laughed at my difficulty, took my leds, and said he would either put them together himself, or if he could find one would buy me an appropriate panel. So, I'll let you know how that goes. It does seem like this would be a good place to establish a cottage industry making replacement enlarger lights!

Cheers, Tim

[Steve Smith]

Your landlord will know this, but here is a simple calculator for the current limiting resistor: http://led.linear1.org/1led.wiz

White LEDs typically need about 3.6 volts and 20mA would be a good current to start with.

With a 12 volt power supply and 20mA through each LED, you will need a 470 ohm resistor in series with each LED

However, it would be better to wire the LEDs into groups of three in series. This would give a combined forward voltage of about 10.8 volts which would need a resistor of 56 or 68 ohms per three LEDs.

This arrangement is more efficient as there is less voltage across the current limiting resistors which means less heat disipated by the resistors.


Steve.