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`May 2003
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`How is white light made with LEDs?
`Presently, there are two approaches to creating white light.
`
`Mixed-color white light: One approach is to mix the light from several colored LEDs
`(Figure 4) to create a spectral power distribution that appears white. Similarly, so-
`called tri-phosphor fluorescent lamps use three phosphors, each emitting a relatively
`narrow spectrum of blue, green or red light upon receiving ultraviolet radiation from
`the mercury arc in the lamp tube. By locating red, green and blue LEDs adjacent to
`one another, and properly mixing the amount of their output (Zhao et al. 2002), the
`resulting light is white in appearance.
`
`Figure 4. Spectral power distributions of several types of LEDs.
`
`Phosphor-converted white light: Another approach to generating white light is by use
`of phosphors together with a short-wavelength LED. For example, when one phosphor
`material used in LEDs is illuminated by blue light, it emits yellow light having a fairly
`broad spectral power distribution. By incorporating the phosphor in the body of a blue
`LED with a peak wavelength around 450 to 470 nanometers, some of the blue light
`will be converted to yellow light by the phosphor. The remaining blue light, when
`mixed with the yellow light, results in white light. New phosphors are being developed
`to improve color rendering as shown in Figure 5.
`
`Figure 5. Spectral power distributions of early phosphor-based white LEDs
`(left), and white LEDs using more recently developed phosphors (right) with
`increased output between 600 and 650 nanometers.
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`https://www.lrc.rpi.edu/programs/nlpip/lightinganswers/led/whiteLight.asp[3/26/2019 4:40:45 PM]
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`
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`How is white light made with LEDs? | LED Lighting Systems | Lighting Answers | NLPIP
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`https://www.lrc.rpi.edu/programs/nlpip/lightinganswers/led/whiteLight.asp[3/26/2019 4:40:45 PM]
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