The maturing of the LED lighting application market has not only seen LED manufacturers aggressively increasing LED luminosity, but also gradually placing more and more attention on the importance in color rendering performance for LED products. Mitsubishi has stated that in the past most sapphire wafers included yellow phosphor in order to create white light, but that the color rendering performance was lack luster. With the evolution of phosphor technology, sapphire wafers to create white light can now also contain green and red phosphor and the same effect happens when UV wafers are paired with red, blue, and green phosphor. This has a clear improvement on color rendering.
According to information presented by Mitsubishi during LED Taiwan conference, phosphor technology is continuing to improve driving the development of imitation sunlight LED light module technology. In the past, adding yellow phosphor to sapphire wafers was the most used technique for producing white light. Mitsubishi believes that this method not only produces low quality in color rendering performance, but also poor color reproducibility.
Due to the visible light wavelength composition of sunlight consisting of red, blue, green, and yellow light, LEDs need to be used in order to get a natural light effect and widen the wavelength of the light spectrum. Sapphire wafers paired with yellow phosphor compared with those paired with blue and yellow (or green) to create white light have a clear peak, but adding in red light weakens that peak. Therefore, when white light is cast onto a red object, such as an apple, the color instead can appear brown.
Mitsubishi has developed two different technologies to combat against the problems that occur when sapphire wafers are combined with yellow phosphor to create white light. The first is to increase the white LED color rendering to above 80. The other is to use UV LEDs with a wavelength of 400nm and add red, green, and blue phosphor to produce white light. Mitsubishi states that this will increase color rendering to above 90 and color reproducibility will be high.
Mitsubishi points out that UV wafers paired with red, green, and blue phosphor technology will have the same light composition as sunlight, with a color rendering index of about 95. When illuminated, light quality goals will be met without the appearance of a multiple array of colors. The application of this technology in areas such as residential indoor lighting, museums, commercial areas, and produce lighting all suit the use of LED lighting products which employ UV light paired with red, green, and blue phosphor to produce white light.