Perfect Lighting

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frederic

frederic

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Thanks to the speedy services of UPS, I now have a small box of white LEDs.

I like LEDs, a lot. They draw very little current, they are fairly bright nowadays, and they are available in many colors. Add to that they are very small.

So, I have a box of white LEDs, I wired up a simple circuit I designed, which limits the current to them, as well as varies the pulsewidth from 5% to 95%, thus changing the brightness from nearly useless to fairly bright.

I'm experimenting with these because halogen lighting is very hot to be near, even with smaller bulbs. Also, with a 7' ceiling height, lights hanging down eat up valuable headroom since both my wife and I are 5'11" or thereabouts. The heat issue is important for several reasons - to sink a fixture in my ceiling, will mean that the electrical box will be to close to the wood sheathing that the slate roof is on. While probably not a bad thing per se, the wood is 61 years old and i worry about an eventual short, and a fire, lighting up my studio brilliantly.

Maybe paranoia, but I'm thinking low voltage, low current, low heat LED's might be an interesting way of lighting the studio and not requiring space above or below the ceiling line.

What do you guys think? Obviously less effective for those of you with the splendor of 20' ceilings, but for guys like me with low ceilings and nasty slants on the same, it might be a good solution.

I chose to buy individual LED's because the commercial 120V LED-filled lightbulbs seem to be 45 bucks or more. True, they last 100 years, but I'm thinking this might be better ultimately.

Time will tell I guess :)
 
frederic said:
Thanks to the speedy services of UPS, I now have a small box of white LEDs.

I like LEDs, a lot. They draw very little current, they are fairly bright nowadays, and they are available in many colors. Add to that they are very small.

So, I have a box of white LEDs, I wired up a simple circuit I designed, which limits the current to them, as well as varies the pulsewidth from 5% to 95%, thus changing the brightness from nearly useless to fairly bright.

I'm experimenting with these because halogen lighting is very hot to be near, even with smaller bulbs. Also, with a 7' ceiling height, lights hanging down eat up valuable headroom since both my wife and I are 5'11" or thereabouts. The heat issue is important for several reasons - to sink a fixture in my ceiling, will mean that the electrical box will be to close to the wood sheathing that the slate roof is on. While probably not a bad thing per se, the wood is 61 years old and i worry about an eventual short, and a fire, lighting up my studio brilliantly.

Maybe paranoia, but I'm thinking low voltage, low current, low heat LED's might be an interesting way of lighting the studio and not requiring space above or below the ceiling line.

What do you guys think? Obviously less effective for those of you with the splendor of 20' ceilings, but for guys like me with low ceilings and nasty slants on the same, it might be a good solution.

I chose to buy individual LED's because the commercial 120V LED-filled lightbulbs seem to be 45 bucks or more. True, they last 100 years, but I'm thinking this might be better ultimately.

Time will tell I guess :)
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Could be a cool idea.

My impression, though, of white LED's is that they give off a cooler light similar to flourescent light. I'm a firm believer that the right kind of light in a room, especially if you have no access to sunlight makes all the difference as far as creating a space you would want to spend lots of time in, so that would probably not work for me.

So far, halogen lights are the best substitute for real sunlight IMO.

Just my $.02
 
You might want to also consider some type of diffuser (like flourescent lights use) or even a fresnell (?) lense to increase the coverage area of your LED array. The direct light from the really bright white LED's can be a little harsh and create a glare.

DD
 
What is the circuit, if you don't mind my asking? Depending on how bright that gets, I could see using that for an effect during a show (sorry, my professional life is breaking in here).

And it is Fresnel, though it is pronounced fre-nell. A bit of Rossco 119 (frost gel) whould be better for killing glare.

If you go to a stadium show, by the way, and you see the big video walls (usually behind the stage) which are so popular right now, those are LEDs. They are made up of thousands of little three LED cells (I believe Sony made the first ones), red, green and blue in each cell. Not really relevant, but cool none the less.

Of course, what I want in my (far in the future) studio is THIS. But that is just because I am a lighting geek (hence the name).


Light

"Cowards can never be moral."
M.K. Gandhi
 
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What is the circuit, if you don't mind my asking? Depending on how bright that gets, I could see using that for an effect during a show (sorry, my professional life is breaking in here).
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I don't mind you asking at all, I've attached the schematic, but its reverse imaged because my website will be dark with bright lettering. The initial purpose of this was a taillight, and the writeup I'm going to post in a second clearly represents that. But, feed it 12V and use the formulas and it will work for any LED.

The white LED's I have are 8000 mcd so they are quite bright. Painful to look directly into. Please ignore the way I wrote it - I'm assuming that the majority of "car guys" coming to my "car site" will not have electronics experience, so I spelled everything out assuming the reader knows very little. I just cut and pasted it as-is to this forum. So, ignore that :)

To the right is a schematic of one LED "bulb". You'll need several "bulbs" to comprise a normal taillight, where you have parking lights, brake lights, and turn signals. LED's being what they are, you can be clever and intermix the three "bulbs" among each other, to create the illusion of one light, with multiple functions. The analogy would be a two-filiment tallight bulb.

The LED's I've chosen are high brightness LEDs, listed down this page in the table, and we'll use those values for this example. Allow me some definitions. A "string" is a vertical line (in the schematic) of several LEDs, five in this case. V_min is the minimum voltage your vehicle will provide, V_reg is the voltage that is typical. Time for some math!

Number of LED's in series:
n = (V_min - 0.9V ) / V_LED
n = (12V - 0.9V) / 2.2V
n = (11.1V) / 2.2V
n = 5.045 LEDs per string (round down to 5)

Since alternators typically put out 13-14V, I used 12V as the minimum voltage to be expected while the car is running. Now, we have to calculate the number of strings, with the aforementioned calculation of five LED's per string. The number of strings is limited only by the output power rating of the NPN transistors you select:

Power Rating = # of strings x current per string x (n x 1.5 + 0.9)
Power Rating = 5 x .030A x (5 x 1.5 + 0.9)
Power Rating = 1.26 Watts

According to Fairchild, maker of semiconductors, their 2N2222A NPN general purpose transistor can handle the load with a little room to spare without having to use heatsinks. The math continues, we have two resistors to figure out. R2 is the current limiting resistor, so lets start with that value.

R2 = 0.7V / (current per string x number of strings)
R2 = 0.7V / (.030A x 5)
R2 = 4.6667 ohms

has 4.7 ohm 25W resistors which will fit this application perfectly. Can't get any easier than that. If you use different LEDs and different number of strings of LEDs, you may calculate out a strange value that doesn't exist, but you can put resistors in parallel, or series, to arrive at different values. Another option is to pick the next higher, but closest size, which generally is close enough. In this case the LEDs would be a "hair" dimmer than the exact value, but still more than bright enough based on the quantity of LEDs in the schematic.

R1 controls the current used to drive the LED transistor (Q1), so we need to give Q1 enough current to switch on:

base current (Q1) = (# of strings x current per string) / 20
base current (Q1) = ( 5 x .030A) / 20
base current (Q1) = .0075A which is 7.5ma

Then using ohms law we can calculate out the value of R1:

R = V / I
R = (V_min - 1.4) / .0075A
R = (12 - 1.4) / .0075
R = 1433.333 ohms

A strange value, but a lessor value is okay, so we'll use a 1.3K resistor, also available from Digikey. Obviously, any electronic supplier can fill both resistor values, I used Digikey as an example.
 

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Oh, one of the faux pas I had made in the design is not to include a 30 ohm (approx) resistor in series with each string of LEDs, so stick that in!
 
Throw in a 555 chip, and you could have a neat little christmas sparkling lighting effect! With more advanced logic, you could have the main lights always on, but have red and green and blue lights fade in and out around the studio. Now that would be cool!
 
The last couple of years we've begun using similar concepts for aircraft lighting to replace the fluorescent bulbs that cost $50 for every 3 ft and break if you sneeze in their direction. The coloration is still an issue, which some manufacturers are experimenting with actual RGB LED arrays that can allow the color to be set to the user's preference via laptop.

I have thought about a couple of studio lighting accessories such as the postlights on rack power supplies and for mixer lights, but haven't done anything with my ideas. I remember the pictures that Rick Fitzpatrick had of his studio with the light strings, and there is probably a way to do that with LEDs also.

Darryl.....
 
I have thought about a couple of studio lighting accessories such as the postlights on rack power supplies and for mixer lights, but haven't done anything with my ideas. I remember the pictures that Rick Fitzpatrick had of his studio with the light strings, and there is probably a way to do that with LEDs also.
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I shoved 48 LED's into a solderless breadboard, added the two transistors and the resistors, and gave it 12V.

Right in my face. Doh! They are definately bright.

So, last night I brought the solderless breadboard upstairs into the disheveled mess of a studio, taped it to the ceiling, then flipped off the two worklights.

48 white LED's (8000mcd each), even though they are angled randomly from the breadboard, are bright enough to light up 1/2 of the room if I face it that way.

I tried fanning them out a bit to cover more area, then angle them down the slant of the ceiling, this really has possibilities.

However what you guys were saying about the color, yeah, well, its not halogen white, i.e. a pure white. Considering how much of the room I've ripped out already, its hard to really determine if its an acceptable form of lighting, or not.

I've decided not to be an idiot, and instead run electrical boxes like I initially planned, and install one on the ceiling slant above the console table area, so if I had to, I can run tiny halogens on a dimmer, as well track lighting around the edges of the room, and two 4' flushmount flourescents down the length of the straight part of the ceiling (for general working, moving gear around, etc).

What I was really picturing the LED's being used for, is hanging over the console table in a long row, with black heat-shrink tubing on the LED, so the light only goes down and not in my face. Kinda like mini BNC lights that a lot of larger consoles have, but off the ceiling slant.
 
Frederic,

Another possibility on your last paragraph idea would be to take something like 1" diameter PVC pipe and cut off one side to make a half-round channel. Then you drill holes for the LEDs which will mount up inside the concave section of the half-pipe. This could be installed easily as a light bar across any area you like. To protect the wiring on the top side you could use some small spacers with screws to attach the other half you cut off.

Your concept is exactly what I've been thinking about for an application. If you wanted to go for something that would have the coloration desired for some general lighting, you might be able to use a percentage of other color LEDs that will alter the overall whiteness somewhat but still remain generally white (ie. say every 10th LED is red, for instance).

Another way to alter the color would be to use pieces of the gel they use in theatrical lighting. I don't know what all colors are available, but it could at least make for some neat effect lighting if nothing else. A light diffusor like they put on fluorescent lights will also break up some of the harshness, and a little bit of creative altering to the diffusor would effectively alter the color of the visible light, also (ie. rusty water stains, a mudbath with a bit of residue left behind, maybe even a very thin coat of paint).

Man, now you've got me seriously thinking about this.

Well, have fun with whatever you decide to do.

Darryl.....
 
DDev said:
Another way to alter the color would be to use pieces of the gel they use in theatrical lighting. I don't know what all colors are available, but it could at least make for some neat effect lighting if nothing else.
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You can get any color you want. We also have a very wide range of diffusion options. As to adjusting the color of LEDs, you would want some type of color correction gel, which is for almost exactly this purpose. Remember, cameras (particularly video cameras) are very sensitive to color temperature, so we need to be able to match the temperature of different types of lamps on a daily basis (halogens, incandescent, arcs, etc.). With LEDs you would want some gradation of CTO (color temperature orange). I would start with either Lee 205 (1/2 CTO) or 206 (1/4 CTO), or the equivalent from Rossco or Gam. You might also try a Bastard Amber (I swear that is a technical term), one of the low Rossco numbers (I can't find my gel swatch book from Rossco right now) or Lee 103. A double cut (two layers) of Lee 152 would also be cool, a very nice, soothing pale gold.

Like I said, I am a lighting geek.


Light

"Cowards can never be moral."
M.K. Gandhi
 
To protect the wiring on the top side you could use some small spacers with screws to attach the other half you cut off.
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Hmmmmm. I thought a lot about your suggestion, and its a darn cool idea.

And to protect the wiring, I could use the other half of the lengthwise cut pipe, glued on top, cut facing down:

End View:
__
/__\
/ \

Since LED's last 100K hours, soldering it up then gluing it together would be fine. Great idea, thank you.

be able to use a percentage of other color LEDs that will alter the overall whiteness somewhat but still remain generally white (ie. say every 10th LED is red, for instance).
Click to expand...

How does one go about selecting the color mixture, i.e. what would be "right"?

Another way to alter the color would be to use pieces of the gel they use in theatrical lighting. I don't know what all
Click to expand...

Easily attainable.

effect lighting if nothing else. A light diffusor like they put on fluorescent lights will also break up some of the harshness, and a little bit of creative altering to the diffusor would effectively alter the color of the visible light, also
Click to expand...

I could paint the inside of the PVC tube halves any color, no problem at all. For a diffusor, if a flourescent light diffusor is the right think, I could very easily slice a 4' replacement diffusor lengthwise and glue it to the face of the PVC along the lengthwise cut lines.

And it was suggested to use a 555 timer for dimming functionality, just finished building a circuit I found on the web, very nice indeed. 5-95%.

Well, have fun with whatever you decide to do.
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Thanks!
 
You can get any color you want. We also have a very wide range of diffusion options. As to adjusting the color of LEDs, you would want some type of color correction gel, which is for almost exactly this purpose. Remember, cameras (particularly video cameras) are very sensitive to color temperature, so we
Click to expand...

How does one go about figuring out the right gel,or light color?

I am particularly fond of halogens, as they are bright white. Flourescents lighting doesn't bother me at all, except I can see it flickering.

Like I said, I am a lighting geek.
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way cool :)

*I* am not !
 
frederic said:
How does one go about figuring out the right gel,or light color?
Click to expand...


You contact your local gel supplier (look in the phone book) and ask them to send you a gel swatch book. They are usually free. You then look at the light in question through one of the gel swatches.

For color correction, if you want it to be a little warmer, you get a CTO (probably a Lee 205 or 206), if you want it a little cooler, you use a CTB (Lee 202 or 203).


Light

"Cowards can never be moral."
M.K. Gandhi
 
After thinking about this and seeing the info Light provided, the best route is probably to go with a gel rather than trying to get a color with different color LEDs mixed together. To really do that right you need at least 2 or 3 parallel rows with the LEDs kind of staggered from row to row to get the light to actually blend before it gets to the viewing surface (ie. diffusor or lens).

I've got a lighting supplier that I'm currently working on an interface with for a new aircraft that has developed an RGB LED on a chip that is configurable via databus for color, brightness, etc. I imagine their product is going to be fairly expensive since they are targetting the aircraft market which is a fairly small market and requires mega-$$ in testing a certification before being being allowed on a plane, but I could envision a simple version of their product also being used. The advantage of their product is the actual LEDs on the chip are quite small so you have a much higher resolution with no noticeable separation between lighting elements. It makes for an LED that really does simulate a fluorescent bulb, and it can be programmed to change colors however desired.

I'm going to have to play with this myself. It sounds like a fun project.

Also, Frederic, on gluing the 2 pieces of PVC together, the only reason I didn't suggest that initially was that I wasn't sure if the top piece would sit on the bottom piece with enough clearance for the necessary wiring.

Anyway, more food for thought.

Cheers,
Darryl.....
 
I read somewhere that you can use ultra bright leds for a DIY projector, along with a LCD screen. You then get rid of the pricey lamp, the noisy fans, and the cold mirrors. Anybody knows of any project like that for semi-dummies like me? Cheers, Andrés
 
:eek: :eek: :eek: :eek: OMG, frederic, my workbench is covered with tons of LED stuff for the studio. You should check out Auto lighting as well. Tons and tons of stuff. Computer lighting, signage, hunting/sports/toys...man its getting into everything...even my STUDIO ART. Hey, why cant you embed them in the lava in a lava lamp :eek: :D
 
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