Color reproduction
Despite the fact that these big-LES light sources need a very large optical system (such a TIR lens and reflector combination) to deliver a directional light output and a regulated beam angle, COB LEDs are a common form of light source for architectural-grade downlights and spotlights. High fidelity color rendering is an essential component of lighting design for retail and hospitality settings as well as museums and galleries. Currently, a metric known as the color rendering index is used to gauge color quality (CRI). However, the CRI number Ra does not account for the light source's capacity to accurately portray intensely saturated colors. R9, the index for a saturated red, is thus occasionally mentioned separately in addition to the CRI general index. To disclose the actual character and quality of goods, to create a visually pleasing atmosphere, or to emphasize the texture, color, and shape of exhibits in the aforementioned environments, a minimum Ra of 90 and R9 of 60 are typically necessary.
A phosphor-converted LED needs its phosphor emission to cover as wide a wavelength range as feasible in order to accurately portray colors. However, there is currently an inherent trade-off between an LED's luminous efficacy and CRI in phosphor-conversion systems. This is due to the large Stokes energy loss brought on by wavelength conversion at the broad FWHM red and green phosphor bands. The use of a narrow-band red phosphor and quantum dot down-conversion of the blue light are two methods being investigated to get around this restriction. The favored method for creating spectrally narrow primaries has emerged as using quantum dots.
