ddrueding said:
I'm still interestd in going the LED route, but am curious how much power/light/heat I'm going to have to deal with.
If you have 1000 watts of halogen bulbs then that's roughly 15,000 to 20,000 lumens. I could be more exact if I knew the specific bulbs. In any case, you're looking at 300 to 500 watts worth of LEDs to replace that. Forget the 5mm and 10mm ones. Granted, right now they're more efficient than the power LEDs such as Luxeons, but only by about 50%, so you'll still need about 350 watts worth. On the downside, since you can only drive them at roughly 30 mA each, and you'll be getting 5 or so lumens out of them at that current level, you'll need at least 3000 for this project.
Are
these the brightest comonly available LEDs?
They're bright but brightness doesn't directly equate to lumens. Those have a very narrow bean angle, and the tints are wildly inconsistent.
Are they appropriate for my use?
Is this a good price?
In a word, no. Me and other people have run tests on these. They lose half their brightness in the span of a few hundred hours so they're really only suited to intermittant duty items like flashlights or bike lights. In fact, the same problem exists with all 5mm LEDs, and more so with the cheap Chinese ones on eBay. Granted, the better ones don't dim significantly until a few thousand hours so those might work for you, but the eBay ones are hit or miss in that area. Some may last, most don't. Nichia 5mm may be your best bet but they run $0.53 or so. You'll need at least 3000 so figure on spending over $1600. You can get them
here.
A better bet is power LEDs like Lamina or Luxeon or Cree. Per lumen Crees are probably the cheapest. Each Cree LED puts out roughly 55 lumens and costs $4 (maybe less in large quantities). For this project you would probably need about 300 LEDs and at about 1.05 watts each they would use ~315 watts. Naturally, they need to be mounted on a heatsink. My reason for suggesting power LEDs is durability. Most are rated to last 50,000 hours so you'll never have to worry about them dimming.
What would I need to do to mount them?
I'm roughly familiar with the wiring needed to finish off the job, but suggestions on AC->DC power supplies with an output near the correct voltage and of a sufficient size would be appreciated.
They would need to be mounted on an aluminum heat sink, and given the size constraints the heat sink would need to be fan-cooled. You could also have many smaller heatsinks if you want steerability but since Crees and other power LEDs are wide beam angle you would need a lens to focus them. For wiring I would put them in 100 series groups of three, with each group controlled by a 350 mA constant current source. For power a PC power supply might do, but you would need one capable of putting out about 35 amps on the 12V line. Alternately, you could put the LEDs in longer series strings and run them directly off rectified 120VAC. Figure filtered, rectified 120VAC would give you about 165 volts. Allowing about 3.5V per LED, and a 5V cushion for the regulator, you could put them in 7 series strings of about 45 (meaning 315 LEDs instead of 300). Overall this will mean a simpler circuit and less power consumption. Naturally, since you'll have high voltages you need to have some means of preventing accidental contact with the LEDs
As I said, I'm not sure you're gaining anything with LEDs over metal halide except durability. If durability is an issue preventing use of metal halide, then consider shipping the booth without the bulb installed, and putting it in yourself before the show. Overall metal halide will serve you better than LEDs (better color rendering, far less complexity, cheaper) but LEDs are possible for this project.
