Instructables

How to EVENLY backlight a sign using LEDs? (similar to a lightbox)

I have a circular sign that is 24" diameter. It is 3" thick and the face has glass with a printed vinyl graphic on the inside. I need the graphics to be nice and evenly bright in the dark, similar to those movie posters, or even a lightbox. I want to use LEDs because I don't want heat and also there's going to be some devices inside so there isn't much room for flourescent or neon. I've done research and found several flavors of led strips but not sure what will be best. What's the best way to back light it nice and evenly? I don't want spotting to occur wherever the LEDs are. I would really appreciate as much detail as possible because I don't know anything about electronics and what components I would need. Thanks alot!

andybuda2 years ago
you can make out where the light is on the canvas but a few pieces of A1 would sort that.. the led strip is 12v on the other picture
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andybuda2 years ago
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IMG_0277.jpgIMG_0276.jpg!C!2(SC!EWk~$(KGrHqV,!h0E0FIIziKhBNE1REq7nQ~~_12.jpg
randyjabel2 years ago
Use a reflective fabric or film on a sheet of plexiglass angled from back to front behind the sign face. Arrange a row of super bright white LED's along the edge where the reflector is at the back of the box, shining the LED's into the reflector, away from the sign face, so the reflector angles the light through the face ( a periscope effect, if you will).
tewharau4 years ago
 Have someone hold two LEDs next to each other behind the sign.  Have them move the LEDS closer to each other until you can't tell there are two LEDs there. That is the maximum distance between LEDs in your backlight array. 

You can then try madwilliamflints suggestion of sanding the tips and see whether it makes a difference to the maximum distance.  If it does, you don't have to use as many LEDs.

Hope this helps.
A couple options: 1) As annoying as it is to do, when I made my Arduino Orb I had a similar problem. What I ended up doing was getting some light sandpaper and going over the LEDs until they weren't clear. Took a bunch of work but the result was outstanding. For your project you could probably get away with just scuffing the tips. (Might not be strictly applicable to this project, especially with that many LEDs) 2) You need something to diffuse the light. You can try putting some steel wool (like a choreboy) over the leds. It's odd how well that can work. Heck, you might even be able to get away with a couple paper towels since they'll let light through but prevent that spotlight effect.
raykholo4 years ago
this is a flyer holder that i made for a school project a while back... its got about 40 leds: yellow, red, and green all diffused to spread out the light more this design is pretty thin though. I made it out of foam core last minute, and it is a brouchure and flyer holder.
flyer + brochure holder.jpg
finfan74 years ago
If your sign has only one face you could make a wide spread array and aim it at the back wall of the enclosure. The light would certainly be more diffused.
dagenius5 years ago
Use fiber optic cables to distribute the light, or make an array of leds.
richms5 years ago
Get milky white LEDs and they will not have the hot spots that a normal spotlight like white LED has. Or sand the white leds down, or put them in a drill press and partilaly drill into the dome to make them scatter rather then concentrate the light
Halvorson5 years ago
Use an electro luminescent light panel (or several for different colors). They are very thin and the control electronics are typically very small.
Diffuse the light before the front panel, have some distance between them and the end result will be smoother...
infared0675 years ago
Diffuser paper usually works good. Maybe find some opaque paper or diffuser paper that will even out the lighting.
PitStoP5 years ago
Can you post a picture to see what it looks like and get a better idea.
110100101105 years ago
if the glass is clear try to light the leds into it thru the edge. uneven lighting is ok here (if not better than even) aim the leds at the back wall of the sign and not forward fluorescents are still option. there are PL fluorescents that are really compact if you use fluorescents protect the wires inside. fluorescents emit uv that makes the isolation on wires crack you can add a dark spot over the lamp itself. use a plate of plastic or metal with fluorescents. use black paint pen with leds
superjames (author)  110100101105 years ago
Thanks for the info. Just to elaborate, the vinyl is attached to the inside of the glass, and there is no space between the edge of the glass and the enclosure. So the lights will have to be behind both the vinyl and the glass. Good tip with the black paint pen!
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