Workstation Light Bar Plan

[curby]

Hello folks, I abandoned the CCFL idea for now and am taking a more normal approach. I'm planning to get some high-CRI Seouls and affix them to some L-shaped aluminum stock. These 350mA, 3.25V emitters will be wired in series to a LED Dynamics Boostpuck. I would have gone with the conventional wisdom and chosen a Xitanium, except that I really want dimming ability.

Attaching an Arduino to the BoostPuck is one of my bigger concerns. Hopefully the Arduino pulls less than 20ma and can be attached to the BoostPuck's 5V reference for power, though depending on the sensors I use (I want touch-free controls heh) this might not be possible. Has anyone used an Arduino/BoostPuck combo? I might need some help on wiring if my intended plan doesn't pan out. :whistle:

Another question I have is what's an appropriate number of emitters. I'd rather have cooler-running, more even light even if I'm under-driving the emitters and spending more money up front. These lights will be mounted to the front edge of an overhead shelf about 50 inches wide, 21 inches from the "working surface" of the desk. Judging from the dispersion patterns, I think 6 emitters 10 inches apart should fit the bill. Does that seem reasonable?

I'd appreciate any pointers and comments you can give me. Thanks!

 

[blasterman]

Bright enough for general computer work. Non intensive reading /writing.

You'd want to double the number of emitters for more serious work. Depends on your eyes.

 

[curby]

Ah, I see. Thanks for the insight. If the entire point is to make it dimmable, then one would expect I'm not always running it at 100%. In other words, I'd like to keep it running low and just blast light when necessary. Any other thoughts? Have people generally had good luck with BoostPucks? All the other threads talk about Xitaniums. =)

EDIT: Apparently parallel strands are scary, so people often recommend driving LED strings in series. The BoostPuck can output up to 48V with regulated current, or 14 of the target LEDs. If I were to use 11 LEDs, does this conventional wisdom of series wiring still apply? In short, should I wire the 11 LEDs in series?

 

[blasterman]

I can't help you with the dimming aspect, but in regards to parallel -vs- series the general consensus is that the more in series the LEDs are the more redundancy you have in terms of stability. There are simply fewer variables for a current regulated driver to go 'wonky' about, and a current regulated circuit in general tends to be more stable with more LEDs in series.

However, that's really splitting hairs. Most of the bad rep that parallel circuits get is from those idiotic 20mA 5mm LEDs that are often driven too hard to begin with. So, when one of them barfs it doesn't take much to start a cascade. I dare say that power LEDs are far more resilient to this problem.

All things being equal - drive is series as much as the circuit will allow. IMHO.

In terms of brightness, what I would do is keep everything open so if you decide you need more brightness you can just order some more and solder them right in line. Right now I have a pile of older Cree Warm-Whites about the same brightness as the Seouls and I'm using them as a reference. My eyes want 9 or 12 of them, but you may be different.

You won't believe the color though. Once you work under a high CRI LED, or good warm-whites at +85 you won't want to deal with incan or fluorescent.

 

[curby]

Thanks again for the reply. I am pretty sure I'll be ok on dimming: I'll simply use a pot to begin with, and then add the Arduino later when I get closer. I sent a message to LED Dynamics for some pointers.

As I mentioned, these lights will be placed in a 50+ inch linear row, for a total minimum wire run length of 100+ inches. Do you have any easy rules of thumb for wire gauge to use? Since this is a static installation, I can probably get away with solid wire if that helps.

Yeah, I'm very much interested in getting nice color reproduction. In fact it might be overkill as it's mostly a computer workstation, but it'll be nice to see what happens. If it works out well I may end up kicking myself for not getting more emitters. =)

 

[blasterman]

I prefer 18gauge finely stranded wire. Why? Because it's super flexible and easy to work. It's typically what you find on your average wall-wart...which is why I never throw wall-warts away but salvage the wire from them because it's rather tough to find in bulk for some absurd reason.

Solid core tends to be stiff, and if you're working with soldering it onto stars it tends to break the solder joint when you bend it where you want it to go. This gets aggravating after awhile.

This is a cool project BTW - you'll learn a lot real quick and you'll be dying to start another project.

I just built yet another lightbar for a sports bar, and spent more time putting nice wood finish over it. Eat that Home Depot. I'm also finishing up another one tonight with half a dozen blue Crees at 700mA used to test growth performance in plants.

 

[Tekno_Cowboy]

I'd go with an even dozen, if you've got the dimming capabilities. That should put you at about 840lumens at 350mA per LED. Dispersed correctly, that is a fair amount of light.

I would suggest setting up with the capability to run near the max rated current of the LED's, for the occasions when you need that extra light.

 

[curby]

Once again, thanks for the input. 12 could probably work, but I'd start worrying a little about heat dissipation. I'm planning on using aluminum L stock. The long leg is 2" long and will be mounted flush to the bottom of a workstation shelf. The short leg is 0.5" long and will hang down along the front edge of the shelf to hide the emitters from direct view. The hope is to reduce glare this way.

The bar itself will be split into a 12" section in the middle, and two 19" sections flanking the middle. Spacing looks something like this:

000000000111111111122222222223333333333444444444455
123456789012345678901234567890123456789012345678901
|_________________||_________||_________________|
  o   o   o   o   o   o   o   o   o   o   o   o

That's 12 emitters with one roughly every 4 inches. As you can see, the middle bar has plenty of open heatsinking space, but the side bars get more emitters per inch of open metal, especially at inches 19 and 31. From the rough specs I gave above, should this be enough metal to run them at 350ma? I believe I read a rule of thumb of 3 in^2 per emitter here on CPF, but maybe it's more. Note that the L bar will be mounted to metal shelving above, but I'm not sure about how well heat will disperse across that bond (i.e. I'm not sure yet how I'll attach the bars to the shelves).

 

[AnAppleSnail]

I believe I read a rule of thumb of 3 in^2 per emitter here on CPF, but maybe it's more. Note that the L bar will be mounted to metal shelving above, but I'm not sure about how well heat will disperse across that bond (i.e. I'm not sure yet how I'll attach the bars to the shelves).

That "3in^2 per emitter" is a broad rule of thumb for bicycle lights - they have air moving over their fins. You've got thick aluminum metal, so if you, say, remove paint from the metal shelf and mount it flush, you'll certainly be doing well. If I drive a Cree at about 4 watts, I can get a 2" square computer heatsink to warm up in still air over a period of about a minute. The important things here are the wattage and the heat path. You'll probably be fine.