I was pricing 8ft fluorescent tubes, realizing their fragility, and trying to find a good use for my Variac other than hotwiring when it came to me…
LED sidelights. LEDs are now pretty bright, and their light is very directional, and they are not fragile. Seeing as my sidelights cannot have shelves on top of them (because of the multipurpose workspace I use), the LEDs fit the bill.
So, I scarfed together some 1/8" hardboard and drilled some holes and routed in some dadoes…
Now I only have to make a rectifying circuit to get the Variac to spit out DC current, and wire up 240 LEDs. Lots of soldering to come…
Hopefully, the LEDs (they’re red, cheapest bright color I could get) will allow me to shape with overheads on, showing shades of ‘pink’ on the blank, the more red, the more vertical the surface, but even if I have to shape with nothing on but the LEDs, it’ll still look pretty funky…
I actually thought a lot about that. Parallel is the way to go for incandescent lighting (like Xmas lights), but not with an led array.
The problem with running 240 leds in parallel is having to buy 240 resistors to get the right current through the leds. Simple math would lead you to believe that the resistors are not necessary if you have an adjustable voltage source, but leds have a very steep voltage/current curve, and I don’t trust my variac that much, nor will I know the power source’s internal resistance once rectified.
Also, since the voltage/current curve is so steep, if there is any slight difference between the leds in parallel, it will show up as a detectable difference in brightness (or ‘smoking’ the leds) without the current limiting resistors in place.
Another thing to consider: wiring them up in parallel (with resistors) would require over 700 solder joints. Running 12 sets of 20 in parallel, I only have to solder around 250 joints, as I only have to solder in 12 resistors.
I’ll be running 6 sets of 20 in parallel for each of the two light strips; so if I lose a section, I’ll only have to check 20 leds, and any differences in led brightness should be undetectable. Besides, the useful life of leds is incredible. Unless you overdrive them, they are good almost forever.
I decided to use the red LEDs because of cost and voltage. My rectifier (been hanging around my garage for a while) can only output 50V, so to do groups of 20 I decided to use red ones. They were also the least costly, like around $0.15 apiece if I remember right.
If I would have had my choice, I would have used green ones, as humans see the color green best. Try this: go outside tonight at dusk and see how a red object turns ‘gray’ before green grass…its pretty cool.
Funny thing. My wife’s job is in semiconductors also. She builds microchips, her deal is etching the metal ‘wiring’ on the microchip with RF plasma reactors. But if I have LED questions, I will definitely let you know, especially if I can’t get this damned thing to work
Have to get to class, but this afternoon will be solder city in my garage…will update when I get the chance…
Ah, this makes sense. I skimmed the list of discussion topics and – just for a second – I imagined leds along the rails of your next board. Yes, I’d go with the colored lights in this case. Maybe red.
I love your idea, how’s the light on your eyes? I didn’t use lots of halogen in my workspace because it gives me a headache (or eyeache?) after a while.
Great idea man…If I didn’t jsut build my light racks I might have gone this way…this way I can justify buying a variac as well lol I know they make ski goggles with red lenses to see changes in the snow better, so the red bulbs might turn out to work really well. Although I haven’t used these goggles so I didn’t really know how well they work. Let us know the outcome.
Good news bad news. The good news is the light strip works. The bad news is that the light is too directional coming from each led, and any slight deviations in the angles the leds are pointing makes for a mottling in the light shown.
Here are some pics:
The array from about 30 degrees above, where not much energy is directed:
Here’s a shot with the overheads off, but sun shining in:
Most of the mottling is from the wires in front of the array, but some of it is from the slight changes in angle of the LEDs. If I were to do this again, I’d use leds that spread their light over a bigger angle. What I can do is ‘diffuse’ the light coming from each, by sanding the lens with some 600 grit, to make it like ground glass. I’ll try it on a small test array before I try it on the real deal.
Here’s a shot with 1 overhead on (behind me) the sun still overpowers (imagine that!).
The good news is you can still make out the bevels quite nicely, but the mottling is more pronouced, but I am being very picky, and some of it is from the the wires in the way…
Overall, I’d say that unless you have to, or you can afford an array large enough (like several rows of the array pictured really close together, or one of the pre-made ones like janklow posted above), flourescents with a shelf to baffle the light away from your eyes are hard to beat. I just couldn’t deal with the fragility of the fluo tubes hanging from my ceiling, as I use the garage for everything, all of my cabinets are on wheels to set up for various things.
I’m not sure about that, give me the weekend to get it all set up (I still have to solder the other side and wire everything up well), and I’ll update then…hopefully it’ll be better once I can adjust the height of the array…
R = 1 ohms 
R = 1 ohms 
R = 1 ohms 
R = 1 ohms The wizard says: In solution 0: 
