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How do I compare the brightness of different LEDs?
Generally LED intensity is measured in mcd (millicandela). Due to advances in technology some very bright LEDs are now called out in cd (candela). It is always important to know the intensity in mcd/cd and the full angle of illumination taken at specific drive current (measured in milliamps, mA). To accurately compare one LED to another, the Angle of Illumination and current levels must be the same. One must also be careful to verify the published specifications from any supplier. Recently the latest technology wide-angle LEDs that put out light flux similar to incandescent bulbs have intensity readings called out in Lumens. These lumen readings, taken at a set drive current (mA), remain the same regardless of beam angle.

Are discrete LEDs and LED clusters dimmable?
Yes, polarized, Bi-polar, diode and resistor LED circuits and or LED clusters/lamps are Dimmable. With Voltage reduction LEDs dim almost linearly as opposed to faster drop in intensity like Incandescent lamps. Important thing to remember is that all LEDs have a Turn-On Voltage. This is the voltage that will start the minimal flow of Current through the LED. A single chip Red (R3K), SP Red (E3K), Orange (O3K), Yellow (Y3K) and Lime Green (G1K) are typically 2Vf at 20mA but Turn -On voltage of these LEDs is somewhere between1.6Vf to 1.7Vf at 1mA. That means a single LED will dim linearly down to 1.6Vf to 1.7Vf and then turn off. In LED Clusters, the Turn-Off voltage depends on how many LEDs are connected in Series or how many LEDs you have on one circuit. LEDs can be dimmed with Potentiometers. The resistor value has to be based on the LED and or LED cluster. In the electronics industry, dimming is achieved by varying Pulse and Duty Cycles of the input voltage.

White LEDs, what can they illuminate? Can I use White LEDs to light up different color lenses?
White LEDs are made by placing a yellow phosphorus coating over a 470nm blue LED chip giving the white LED a cool white or florescent appearance. Previously, the lack of white-light LEDs has limited the integration of LEDs into a wide range of applications; however, now, the misconception exists that InGaN-white LEDs can illuminate a lens of any color thereby simplifying lighting requirements and designs. This is not completely true. Since the colors red and green represent a very small part of the color scale in the white LED, white LEDs should only be used behind a clear or milky white lens or panel. Place white LED light behind a red lens and the light produced is a pink color, a yellow lens turns a lemon-lime, green lens shifts to aqua and orange lens becomes yellow. To maintain accurate and brilliant colors, it is imperative to match the LED color with the lens color. In short, white LEDs made from a blue chip should not be used as a general backlighting light source for different colored lenses and panels.