This is really cool stuff!!! have you considered firing the lights into some sort of reflector panel that runs
the length of the lights? (maybe have the lights fire upwards into an angled panel that is painted white?)
Might be too diffused, maybe some flat clear spray on the diodes?
Watching this thread with interest…
I thought of that too!
John, I bet you’re thinkin’ of that already too.
Why not use a diffuser from a fluorescent light? Bunch of things you could use to diffuse the light but the problem is going to be that most will reduce the amount of light coming through. Softboxes in photographic studios use a piece of lightweight white fabric to diffuse light, or you can use tissue paper, or all sorts of things. No need to mess up all your leds.
Hi Maxmercy,
Great idea!
Why not use aluminum tape as a reflector/diffuser.
A layer of clear spray paint to prevent oxidation.
Keep up the good work!
Soul
OK,
now that everything is wired up, I got to test the thing at dusk. I still have to get some hooks and light chain to hang them from the ceiling, but the question of whether or not they would have enough light power to shape without using an overhead light has been answered (please forgive the immense mess):
They are damn bright! Also, the mottling I saw when I was testing the first strip disappears and blends well if the object being illuminated is 30" away or more…whew! So, it looks like they will work just fine. If you wanted to illuminate objects that will be closer to the strips, I would use leds with a wider dispersion (mine are 15 degree dispersion, very narrow, almost bit me in the ass), or more rows in the array. Also, I would buy a 5mm drill bit to match the led diameter. I used a bit slightly oversize (what I had), and it added to the misalignment of some of the leds because of the play the leds had in their holes when I glued them in.
All in all, a good learning experience, and I now have sidelights!
JSS
Hey CG,
The red light is nothing new for me, we used to use it all the time at night in the Marine Corps, so I’m used to it. If I get it dialed in the way I want, I’ll be able to use overheads as well as the sidelights and have shades of pink show me the contours on the blank…
JSS
Hey PlusOne,
It turns out the mottling deal was solved by just increasing the distance of the strip to the blank. The pics showed the blank about 18 inches away from the strip, but at 30+ inches, the mottling disappears. Also, the light strips are sensitive to the height they are placed at realtive to the blank, so I’ll have to have some adjustability for that.
All of this could have been avoided if I used less directional leds, mine output only a 15 degree cone of light. 30 degrees would have worked better, but then more light would get to your eyes as well…it’s a trade-off (isn’t everything?).
I’ll update again when I have them mounted, becuase I really have to finish shaping this blank and glass it before it gets too cold out here…
JSS
IMPORTANT UPDATE: Well, I got everything all mounted, looking nice and working very well, started finish shaping my blank, and over the span of a few minutes, fried almost the whole LED array, so I now have only 2 strings of 20 LEDs functioning out of the 240. I troubleshot the problem back to the rectification circuit I am using.
Remember that I am powering the array with a Variac. I rectified the AC using a fullwave bridge rectifier. Here’s the problem. I calculated all voltage values based on AC RMS voltage. Upon full wave rectification, the voltage waveform looks like this:
So, you can see how when full wave rectified, the RMS value of voltage is only around 0.64 of peak. I calculated everything off of RMS, ignoring peak, so my LEDs got fried; the peak voltages they saw (however brief) caught up to them. The good news is that as one LED in each string of 20 got fried, it essentially shut off the other 19, so I will not have to replace the entire array. just 10 or so LEDs. But I’m pretty sure the life of the remaining ones is limited due to my dumbassity.
Pretty dumb mistake, and pretty careless. Oh well. Fair warning to anyone who is thinking of rectifying their Variac…remember to think about the whole rectified waveform!
JSS
Rectum…dam near killed him!
Whatch U talking bout willis? Half rectified and shit.
I’m trying to not…
I’d be canning the Variac, go for a transformer or something more stable…
…Laugh?
After realizing what I did (and getting over the fact that I’m gonna have to buy some more leds), this was freakin’ hilarious…
The best part was how I carefully calculated everything so I wouldn’t fry the sum-bitches, and I did anyway…that blank is going to have to wait a little while longer…
Hicksy - considering I already built up the power circuit, and it was my confident idiocy (and nothing else) that caused this mess, the variac will probably stay, unless you know of a cheap way I can get a smooth 40VDC without using lots of batteries that I don’t have…good news is I can now get the wider pattern leds…
JSS
…Laugh?
No, the jokes–happens every time I see the word “rectify”
the set-up this time had red lights …
output…
any smoke?
You’re an engineer…
There’s gotta be one in there somewhere.
Hey wait a second…
rimshot
Ouch!
I’ll be here all week!
Sorry mate, I wasn’t making fun of your attempt…
A transformer with 115V input can end up as 40V output if you get one that has the windings coming off at the right spot…
Maybe try Radio Shack (if it still exists) or Tandy…
They’re not that expensive (cheaper than batteries) and you can use the Variac as intended…
Hi Maxmercy,
Try a 28 VAC transformer, it should give you 40 VDC rectified.
LED work on a constant voltage drop with a little of resistance.
They work good on high peak currents, only the average value of the current should stay within the max current limit of the LED.
Use the resistor you put in series with the chain to regulate the current through the LED’s,
Try measuring this current and do further calculations from there, between 10 and 50 mA should be good.
Didn’t the resistor burn, how much wattage did it get?
Just some thoughts
Soul
No need to apologize, Grant, there is fun to be had for such jack-assery. Lesson learned, and no one got injured.
What convinced me that I had fried them was this (from LED Center online):
“The other thing to consider is that AC voltages are usually expressed in Volts RMS (root-mean-square). The concise explanation is that this allows power calculations to give the same results as for DC voltage. But the peak voltage will be higher (1.4 times higher) than the RMS voltage, so when you do rectify and convert to DC, you have to be sure to use the peak numbers.”
and this, which perfectly described what happened, from the same source:
“A typical indicator LED will have a spec that represents a typical point along the operating curve. That would look something like “3.3V @ 20mA typical.” Driving this LED above that point will shorten the useful life. You may also get a maximum rating for either current or forward voltage. Exceeding those ratings will dramatically shorten the useful life, generally ending it suddenly in the process. But driving an LED “hot” will make it burn more brightly for a shorter time. The heat dissipated by the junction has to be conducted through the leads, which aren’t very big and aren’t designed to heatsink the package. When the junction runs hot, the light output will also degrade much more rapidly. You may find that your LED won’t light up at all without being overdriven somewhat. If the package of an indicator LED (the 5mm or 3mm types) feels hot, you are definitely overdriving the LED.”
I essentially overdrove the array by not taking into account peak voltage numbers, and just using the averages. That’s what I get for not thinking things through all the way, but oh well, I’ll have the array functioning again hopefully by the end of the week. Then I’ll snap some pics of what a properly driven array looks like, not the super bright ‘nuclear reactor’ version in the last pic above…
JSS
Hey soul,
The resistors didn’t burn, they are 1/2W resistors. The peak current pulse width is what I think got me, because led spec sheet says not to pulse more than 0.1ms. The transformer I have is variable, so I can dial in the VAC I want, I just didn’t account for RMS vs peak. So, when I did all calculations for 2V to each LED, I didn’t take into account that this was an RMS reading, and that each LED was briefly seeing around 2.8-3V every 1/120th of a second. After a while of that, the leds decided they were just going to quit, and I don’t blame them.
I’ll update when I get the array back online.
JSS
Update:
Well, I replaced the bad LEDs, made a real control box, and rewired the power source so as not to overdrive the LEDs.
Here’s the control box:
And here’s the final result, the light is very directional:
and with a slight tilt to the blank:
Sorry the pics suck, but I had to compress them a lot. Bottom line is that it works, and works well now. Best of all, the whole array only draws 300 mA, that’s the equivalent of a 10W light bulb, a little more due to the AC to DC conversion. Not bad, compared to the 200+ Watts being pulled by two 8ft tubes…
With a well designed array for more usable light (like 3 rows 3/4 of an inch apart of the ones pictured above), you could have a plenty bright array with light that won’t get in your eyes, and will only pull 30-40W, around 1/3rd that of two 8ft fluorescent tubes. The startup cost would be more (around $200 + the labor to build the array), but it would pay off every month in lower electric bills…
JSS
Really pleased your lights worked out MM…
This would rank high in the “Sways thread of the month” in my opinion…
Good stuff…
MM even if it didn’t work – just having that cool laser-wash light look would be the mutt’s nutts 
Congrats – great stuff!