I got my hands on an old slide projector (the kind that projects cel slides onto a wall).
The light source, is a 24V, 150W incandescent halogen lamp.
As a little pet project, I'm thinking of converting this projector to LED, using a high power LED. To do that, I need to remove the lamp mirrors, replace the existing lens with a reflector and collimator lens, add a heatsink, etc.
But before even attempting this, I need to know how much light I need.
I've used a conversion table to estimate the number of lumens that I need. My estimation is between 3.6klm to 5250lm (I've used "tungsten quartz halogen (12–24 V)" and "photographic and projection lamps", I don't really know which one is applicable in my case).
Only once I know how much light I need, I can deduce what kind of high-power LED I need.
- I have no experience in photometry as such, is using Lumens as a comparison value even applicable?
- Are my estimations correct?
I was looking at getting a 100W LED, which supposedly provides 10klm, and then add a PWM controller to dim it, if necessary. But it seems that a 100W LED is pretty overkill to me.
Best Answer
Your calculations are correct, and you should probably figure on about 5000 lumens. Projector bulbs aren't expected to last nearly as long as, say, overhead lights, so they are driven harder for greater efficiency.
However, be warned that getting your optics right may be more of a challenge than you realize. A good condenser works on a small light source, such as the glowing filament, but LED bulbs are a much larger source since they use a phosphor coating on the bulb envelope. This will make it much harder to get good light concentration on the slide, and you may have to use a more powerful LED than you had originally thought.
It's fun idea though. I wish you luck.