LEDs for general illumination: The state of the science

Light emitting diodes (LEDs) are emerging as a viable source for the general illumination of the built environment Recent product development efforts have focused on four areas: increased light output, increased conversion efficiency, minimization of color shifts, and increased color rendering index (CRI) for white LED sources. Although little can be argued against the first three areas of development, using CRI as a spectral design criterion may be misguided. Other measures of color preference or color discrimination may be better suited to optimize LEDs for general illumination. In the future, due to the nature of the LED spectral distributions, virtually any source spectrum may be possible, which begs the question: should product development efforts aim to match reference sources that are not optimal in terms of color preference or discrimination? This paper summarizes current theories about LEDs and color. Color shift is discussed as it relates to temperature, age, input current, and dimming. The methods of making white light with LEDs are described and contrasted in terms of chromaticity coordinates, correlated color temperature (CCT), and CRI. The colorimetric potential of LEDs is discussed in consideration of numerous measures of colorimetric performance.