Solid-state lighting (SSL) is increasingly being introduced into the market and it is expected that many of the light sources currently used for general illumination will be replaced by light-emitting diodes (LEDs) in the future. As the spectra of LED sources are dissimilar to traditional incandescent and discharge lamps, some of the existing standards and measurement methods are insufficient or deficient when applied to LEDs. For example, a new metric for color rendering of light sources is being developed to address the problems of the color rendering index (CRI) for LED light sources. Such studies require well-designed vision experiments. Because solid-state lighting sources have much greater flexibility of spectral design than traditional lamps, manufacturers have more freedom in the selection of correlated color temperature (CCT) and color quality of solid-state lighting products for various lighting applications. However, the interrelated effects of chromaticity, color rendering, and other aspects of spectra on lighting are still not well understood. Thus, the introduction of solid-state lighting necessitates re-visiting many of these questions regarding the effects of spectra on lighting.
To address such important issues and to allow state-of-the-art vision experiments on color and lighting, a Spectrally Tunable Lighting Source (STLS) has been developed at NIST. The facility has two STLS units, which illuminate separate room-size cubicles (2.5 m x 2.5 m) allowing subjects to be completely immersed and adapted in the lighting environment. This enables evaluation of the color rendering of objects, including human faces, in a real-life setting. The two cubicles are adjacent so that side-by-side comparison can be made for different light settings.