Sign & Digital Graphics

September '18

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24 • September 2018 • S I G N & D I G I T A L G R A P H I C S ELECTRIC SIGNAGE W hite LED modules are commonplace for backlighting illuminated signs, and are being used in applications from channel letters to cabinets and graphic advertising boxes. However, not all white LEDs are created equal. LEDs are gener- ally monochromatic, meaning that they emit a very narrow spectrum (band) of light. In order to make white light, LED lamp manufacturers cover a blue LED chip with a phosphor. This phosphor converts the blue light to a broad spectrum. This process adds some art to LED manufacturing, as there can be both variations in the phosphor thickness and distribution. Since this is a batch process, it also can create variations from batch to batch. Depending upon the manufacturing parameters, there are a range of hues of white that are created from a yellow-red to a blue-white coloration. Depending on the applica- tion, these color variations or hues can have a significant impact on the effectiveness, perceived "brightness" and quality of your sign. In this article we will provide an overview of color temperature and color render- ing and how to choose the correct "color" of white to optimize your sign application. First, we need to define some key variables. What is CCT? Correlated color temperature (CCT) is a description of the warmth or coolness of a light source. When a piece of metal is heated, the color appears red in appearance and gradually changes color to orange, yellow, white, blue-white, and finally a deeper blue color. The temperature of this metal is a thermal measurement in degrees Kelvin or absolute temperature. Understanding color temperature and color rendering for LED-based signage applications J. Bryan Vincent is an expert in the field of solid state lighting and electronic materials. He has dedicated the past 10 years to devel- oping LED solutions specific to the sign industry and is a partner at Principal LED. He has a bachelor's degree in Chemistry and a Ph.D. in Chemistry/ Materials Science. Color Temperature Color Rendering Index Which is Better? B Y J . B R Y A N V I N C E N T , P H . D . L E D I N S I G H T S

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