Anyone know anything about Halogen Projector Bulbs

(Gilbert Townshend) #1

Just bought a couple of these 100 watt bad boys for a photographic enlarger I got off ebay but looking at the power ratings and lifetimes (only 50h!) I’m considering how hard it would be to convert something like this to LED, for both heat and lifetime of the bulb reasons.

I have no idea though if it’s sensible to keep the rather bulky 12v (AC) power supply and fittings or try and find something else with the same dimensions and wire that up inside the head instead. There seems to be a fair bit of room, presumably for airflow currently so I get the feeling it might work, assuming I can find something with a similar colour temperature and brightness.

I’m totally out of my depth with working out what bulb might work here, datasheets all seem to be lacking lumen values and I’ve just glazed over trying to google for things and getting useless repeats of things I already know.

Here is the housing currently:

(Rich Maynard) #2

Do modern enlargers use LED lamps? might be worth starting by investigating that.

(Alexander Baxevanis) #3

I think I can help, I used to run the darkroom at London Hackspace, and now building my own at home!

This is the ‘official’ datasheet for the bulb you’ve got:

The colour temperature is 3330K which is probably the same for all enlarger lamps (mine has the same specs, although it runs at 15V, which is the first time I’ve seen that).

According to this the light output is 750 lumen.

You might be able to replace this with one of these lamps:
Some of them reach up to ~650 lumen, which I guess will only lengthen your exposure times by a bit. Possible downsides:

  • LEDs might not have the exact same colour spectrum as an incandescent light bulb, which might mean you’ll need to tweak your filtering.
  • Not sure if all of those LED will work with 12AC supply, they may need a 12DC transformer.
  • You’ll lose a nice heat source for your cold darkroom :wink:
  • You’re still stuck with a giant transformer power brick

My strategy has been to replace the power supply with a switching DC power supply like this:

I’m then combining this with an Arduino and a relay to integrate the timer and power supply into one unit, which saves space results in less clutter. Happy to show you in more detail if you’re interested.

You could potentially find a way to replace it with LEDs, but you’d have to build something like a diffused lightbox that goes directly above the film - a bit like what the Intrepid people have done with the enlarger mod for their large format camera: The challenge there would be to ensure you get a good diffusion with no bright or dark spots.

Anyway, good to meet a fellow film photographer! Let me know what enlarger you’ve got and what you’re interested in printing (colour? B&W? what film size?) and we can discuss more!

(Gilbert Townshend) #4

It’s a colour enlarger that will do up to 6x6 120 film, so altering filters for colour temperature shifts is probably not that hard.

It sounds like I need to go to a lighting shop and talk to someone friendly there. If I can get a reasonably similar brightness bulb with the same housing then power supplies etc might be a pain but should be solvable with a bit of help. There’s a lot of space in the existing one too, I almost wonder if I could add rectification to mine.

What bulbs did you end up pairing with that power supply?

I had considered going in on the intrepid enlarger Kickstarter but as I don’t own a large format camera it seemed like overkill, especially as I got this enlarger (and a 35mm one) plus loads of extras for all of forty quid on eBay.

(Alexander Baxevanis) #5

I’ve kept the original lightbulb and just replacing/building the power supply & timer combo.

In the beginning the 50hr life sounded like a little to me, but then each exposure tends to be less than a minute, so it’s not going to be on for hours on end.

But let me know if you do manage to get it working with an LED bulb, it’s an interesting experiment. Bear in mind that the LED bulb is going to produce some heat too, certainly not as much as the incandescent one, but will still need some ventilation so you probably can’t cram too many electronics next to it.

(Gilbert Townshend) #6

More and more it just doesn’t seem like it’s worth it. I’d have to rectify the AC to dc, which might at a pinch fit in the existing transformer case but also find something of a similar brightness, from a reliable (i.e. not ebay) seller with a high CRI and in roughly the same form factor.

Given all the problems involved it seems like it’s just more sense, unless I start my own print shop, to just use the halogen bulbs.