Understanding LED lighting begins with an understanding of how colors work. A simplified explaination is sufficient for the purposes of this document, but given time you might want to check out a great tutorial on this subject at HowStuff Works.Com.
Basically, objects contain "pigments" that ether absorb or reflect colors. White light contains all colors and so multicolored objects will reflect all possible colors. Shining a pure colored LED light such as "blue" onto an object will only reflect colors back in the blue spectrum.
Here is a multicolored object with a white LED shinned on it. As you can see the object takes the white light and reflects back all colors contained on the object. This is why objects in white light appear to "pop" with color and are vibrant and "real" looking.
Multicolored object with white light
Colored LEDS Only Output One PURE Color
Colored LED lights (and lasers) present a unique situation. Unlike other types of colored lights, they produce pure color and do not output any other colors of the spectrum (remember white light contains all colors). So for example, shinning a blue LED onto an object will only reflect back colors in the blue spectrum. The object will be very bright and vivid, but only a single color will show. It's best to reserve the pure color qualities of LED lighting for special effects such as scares or props that the designer really wants to jump out at the audience. Use filtered white LEDs for scenic lighting (see next section).
Colored LED lights only output one pure color
FILTERING WHITE LED LIGHT WITH A GEL
Because a white LED outputs all colors of the spectrum we can use a "gel" (colored plastic) to filter the light to the desired color. All colors are still passed through but the color of the gel will bring out more of that color in the object. This allows us to highlight a specific color while at the same time still allow the other colors of the object to reflect back..
White LED lights with gels output all colors casting a hue over the object.
The desired color is plased onto the front of the white LED light.
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