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Step 4Shape And Apply Lighting
First:
Slim down an LED. We want to get as much light as possible from our LED into the plastic, so we're going to grind down the plastic shell of the LED to fit better. You can find rectangular LEDs that will be the right thickness, but we find they're rarely bright bright enough and come in limited colors. We used a rotary tool with a sanding cylinder, but you can use whatever works (sanding table, sand paper, grinding wheel, etc). 3mm LED's don’t need much modification, just a tiny bit off the front and back. Be more careful when working with 5mm LEDs since you can accidentally go through the plastic case and remove some of the more important bits of the LED. Work slowly and carefully holding the LED in a pair of pliers to save your fingers. You can also shorten the height of the LED since we don't need the lensing effect of the case.
Second:
Wire up your LED. This depends the details of your project. If you're soldering it will be a lot easier and safer to do it now rather than when it's embedded in the plastic. It's also a good chance to make sure you didn't damage the LED when grinding it to size
.
Third:
Cut a place for the LED in the plastic. Use your rotary tool (or a file, etc) to carve a cutout along the edge the same size as our LED. It should fit snugly with only the wires sticking out. If you're using really thick plastic you can even drill holes in the edge to hold the light.
Fourth:
Hold the LED in place with aluminum tape. Apply a thin strip of aluminum tape along the edge that contains our LED. Make sure it runs on the front and back of the plastic. Cut out a notch around the LED wires so the metal on the tape doesn't short it out. The aluminum tape will not only hold the LED in place but will direct as much light as possible back into the display.
Apply some more reflective tape along the remaining edges. This is optional, but it will improve the brightness of the display and keep light from leaking out.
If you're not satisfied with the brightness of your display add more LEDs along the edge. Very long or large displays will be more evenly lit if you spread the LED's along the edge.
Slim down an LED. We want to get as much light as possible from our LED into the plastic, so we're going to grind down the plastic shell of the LED to fit better. You can find rectangular LEDs that will be the right thickness, but we find they're rarely bright bright enough and come in limited colors. We used a rotary tool with a sanding cylinder, but you can use whatever works (sanding table, sand paper, grinding wheel, etc). 3mm LED's don’t need much modification, just a tiny bit off the front and back. Be more careful when working with 5mm LEDs since you can accidentally go through the plastic case and remove some of the more important bits of the LED. Work slowly and carefully holding the LED in a pair of pliers to save your fingers. You can also shorten the height of the LED since we don't need the lensing effect of the case.
Second:
Wire up your LED. This depends the details of your project. If you're soldering it will be a lot easier and safer to do it now rather than when it's embedded in the plastic. It's also a good chance to make sure you didn't damage the LED when grinding it to size
.
Third:
Cut a place for the LED in the plastic. Use your rotary tool (or a file, etc) to carve a cutout along the edge the same size as our LED. It should fit snugly with only the wires sticking out. If you're using really thick plastic you can even drill holes in the edge to hold the light.
Fourth:
Hold the LED in place with aluminum tape. Apply a thin strip of aluminum tape along the edge that contains our LED. Make sure it runs on the front and back of the plastic. Cut out a notch around the LED wires so the metal on the tape doesn't short it out. The aluminum tape will not only hold the LED in place but will direct as much light as possible back into the display.
Apply some more reflective tape along the remaining edges. This is optional, but it will improve the brightness of the display and keep light from leaking out.
If you're not satisfied with the brightness of your display add more LEDs along the edge. Very long or large displays will be more evenly lit if you spread the LED's along the edge.
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Any gap between the LED plastic and the display plastic will cause reflection at the interfaces. The air gap has a refractive index of 1 (n = 1) while the plastics are about 1.5.
Not the only supplier, but one that is available in reasonable sizes and a variety of sources is Norland optical adhesives. These are UV cure, which I like better than two part, since you don't need to degas to remove bubbles. Leaving the parts in bright sunlight might be enough to cure the UV adhesive.
Think about this for a moment.
Take 2 chromed wrenches with same size and paint 1 white and do nothing with the other one. Hang both wrenches on a string in full sun for lets say 30 minutes and touch both wrenches after that.
You will find out that the unpainted chrome wrench is much hotter than the painted white one, because the chromed wrench absorbed more light. I don't know what is worse, a chrome wrench or black painted wrench left in the sun.
What I would do, sand the edges with very fine sand paper and polish the edges, then paint them with a shiny white paint.
Also, I would use clear epoxy to hold the LED's to the plexi glass and fill all the gaps.
With all due respect to the author, who said-
"Using reflective material will reflect more light back at the same shallow angle it needs to stay inside the plastic. Silver and aluminum are very nearly purely reflective (At least in visible light)"
All of my college classes that touched on reflectance of light did mention that white is a better reflector than "silver" which is gray, which is partly black. The flatness of a surface enhances reflection, and mirrors show an image better because of the absorption (blackness so-to-speak) of some of the light.
Taking into account the amount of light reflected versus the quality of a specular reflection from a standard mirror... the photometer reads more light coming off a pure white surface. Paint is often too rough, thus diffuse reflections result. So the choice of materials will affect the angle of reflection, or diffraction, or refraction, etc. depending upon the optical design.
When containing the light within the clear sheet, polished and flat edges are preferred. And a smooth reflective backing such as foil tape is an easy way to get a much flatter surface.
In a theoretical perfect world, one might want to use a nano particle sized coating of Titianium dioxide applied to a perfectly square and flat polished edge... HA! (Not going to happen for most of us unless we have access to optical fabbing equipment!)
If you look at the aluminum tape it is actually white on the sticky side. But unlike using plain white tape it's also optically opaque, so the light it doesn't reflect it absorbs, which enhances the effect.