Revisiting Old Projects
Today while cleaning up the lab I came across a little blue ball lamp thing which was my first ever LED project some many years ago. I had found the little guy at a garage sale and later swapped out the incandescent light bulb inside of him with a small array of 22 blue super-bright LED’s.
Not really knowing any better at the time, I had wired all 22 LED’s up in parallel with each other, all of them “sharing” one resistor. Ah how naive. No wonder the lamp got progressively dimmer and dimmer over the years as the LED’s fought each other over current, seeing which of them could burn itself out first.
For fun and nostalgia today I decided to revisit my little blue ball lamp and do it proper (or at least more proper). I yanked out the (now half-dead) 22-LED array and replaced it with a 5-watt blue power-LED.
The LED was a “ProLight 5-Watt” (cheap Chinese knockoff basically) which I glued to the back of a small heatsink with thermal epoxy and also glued a LM350 voltage regulator in a constant-current configuration to drive it.
The only challenge was figuring out at what current would be safe to drive the LED with the heatsink I was using so that the LED wouldn’t damage itself. As per the spec-sheet, I had to keep the junction temperature (the temperature of the LED chip itself, buried deep inside its packaging) below 135 degreesC.
In this case a current of 400mA seemed to keep the approximate junction temperature (as measured with an IR thermometer through the LED’s lens) below 85 degreesC which gives a reasonable safety margin.
The result is a lamp that is substantially brighter than it ever has been (with incandescent bulb or otherwise) and will probably last a lot longer.
March 3rd, 2008 at 1:31 pm
I want a bob-omb lamp! Where could i find one of those lamps?
March 3rd, 2008 at 1:43 pm
Beats me! I found that lamp at a garage sale some, oh, 6 years ago probably.
March 3rd, 2008 at 2:12 pm
Where did you find the actual sphere? Any suggestions?
March 3rd, 2008 at 2:30 pm
When I say lamp, I mean the sphere too. I.e. I found it at a garage sale and have no idea where it came from originally. There’s absolutley no writing on it anywhere which would give me any clues. Sorry :(
March 5th, 2008 at 1:34 am
I have seen these called crushed ice lamps - I have one too, but the bulb doesnt have the clip arrangement, it just pushes thru a hole in the bottom. Had to find a small ES pilot lamp for it which was a challenge when it burned out.