Invite the inspector to touch his nose to a operating 3W LED, and then to an operating 12-volt halogen bulb. Better yet, in the interest of safety of course, invite him to use a more southern and more sensitive temp-test probe to protect eyes from bright light....
They actually produce about the same amount of heat. It's just that the LED has to be heatsinked, or it'll explode. If LEDs worked at 500C, then they wouldn't be heatsinked so well, and would get just as hot.
Don't forget the *other* big conflagration:
It may be that the first fire also tends to polarize the chicago fire inspectors!
As I said before, Mooooooooo.
Jim
If you want to get really fancy you could use clusters of 3 Luxeon IIIs with PWM drivers. #18 wire would carry 1 amp @ 12V (to drive 3 3.9V LEDs) up to
40' so the drivers could all be mounted on one centrally located board with the microcontroller. The drivers could have digital pots so the lighting sequences can be controlled by a microcontroller. The microcontroller could set some random pattern and speeed based on something like the room temperature or noise level. Maybe even a capacitance sensor pad so the viewer could participate.Luxeon IIIs are not cheap but I would lay odds that you could get a deal on
150 to 200 of them. Any electronics geek with a little patience could build an addressable 50 circuit controller board for under $500.Another alternative would be to use regular 12cd hi-bright LEDS mounted directly to the glass. The light would enter the glass and come out at the edges and imperfections with no light wasted. Also by combining red green and blue LEDs you could change the colors as well as the brightness. At $.50 each retail those would be a lot cheaper and the total amout of light required would be less. I have used that method for some etched Lucite restroom signs and it works really well.
They wanted to see UL stickers on everything that plugged in. And they have a lot of authority. We certainly felt cowed.
Best regards, Spehro Pefhany
Yes, but surface temps are markedly different. Few materials ignite at 75C but ya don't want a halogen bulb in the powder magazine!
Cost per lumen is about the same. White Luxeon III's were $8.50 ea last time I bought. I think the price break on Luxeons is at about
2500 pcs.Yep. LEDs respond quite quickly to the voltage level, usually in the megahertz region and 60 hertz is a very low frequency. You can backbias a LED to several times the forward voltage (if you're worried about this, put another LED in there pointing the other way and it will be on when the other is off) without problems. There is a spec on how much back voltage that any particular LED will take without problems. If you use a regular light dimmer control for brightness, the brightness level will be rather nonlinear as the dimmers do their work by being off until a certain time is attained in the sine wave period of the incoming power. This will mean that the low levels will be very nonlinear due to the low voltage that comes out. The short time period plus the low voltage is where the problem (if you want to call it that) happens. Using DC plus the cap will average out the voltage and that will tend to linearize the brightness vs. position of the dimmer knob.
-- Why isn't there an Ozone Hole at the NORTH Pole?
One thing to remember is that with LEDs, the light is directional to a fair degree so they don't need reflectors to reflect the light to the area of interest. This will magnify the lumens that are viewed by some ratio. In the relativey early days of using LEDs for indicators, the problem with the LEDs as that they didn't have the wide angle light production so there had to be some piece of material to widen the light so that it could be seen brightly way off-axis from the direct on viewing position. The LED indicator was brighter on-axis than the incadescent bulbs were but the off-axis light output caused the LEDs to not be used so much as they were dimmer in those directions. Eventually light output got high enough in LEDs that they could use frosted plastic in the construction and thus be used for that application.
-- Why isn't there an Ozone Hole at the NORTH Pole?
Luxeons are not very directional. The radiation pattern of the Lambertian model approximates a cosine curve, with luminosity down to
50% at about +/- 50 degrees off axis. The batwing and sideshooter models emit more of their light sideways, less on-axis. The sideshooter is visible over 360 degrees, is designed for use in a parabolic reflector.A bare Luxeon acts more like a "bare bulb" in front of a flat reflector. A reflector or collimator is necessary if directionality is desired. Good molded acrylic collimators are available for about $3.50 in unit qty. Beam divergence angles are available from "flashlight" (
At 1A, you've got around 3.5W that has to be dissipated. Have you had any problems keeping the die temperature down on the Luxeons at full current?
Best regards, Spehro Pefhany
No, but they do need a heatsink. Theta j-c is 13C/W for the emitter, max rated die temp is 135C, so theoretically if the case is kept below 70C you're OK. I don't like to run them that hot, though. The star is 17C/W.
I have a 3W emitter (not a star) mounted on a 3/8" dia aluminum post about 1.1" long with a 2" square piece of 0.100" thick aluminum on the other end of the post. With the thermal epoxy, I probably have about
17C/W, junction-to-post. (The post is so I can poke it into a reflector)At 1.000 amps the voltage on this particular part is running 3.517 volts at temperature. The post settled out at 55.2C right near the LED. The plate is at 52.3C. Ambient in the lab is 19.5C
Aavid Thermalloy has a selection of heatsinks specifically recommended for Luxeons.
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