USING BRIGHTNESS AND COLOR GAMUT TO ASSESS SPECTRA OPTIMIZED FOR LUMINOSITY AND COLOR RENDERING

摘要

General-purpose white-light sources are traditionally optimized for both high luminous efficiency (efficacy) and high color rendition. Maximum efficacy corresponds to efficient use of electrical power for economical operation. High color rendering corresponds to the ideal that objects illuminated by the source should have the most similar possible appearance to objects illuminated by a corresponding blackbody or Planckian radiator. Much can be learned from manipulation of the spectral power distribution φ(λ) of a light source without reference to the physical properties of a particular lamp. In particular, one can separate the lamp efficacy into (ⅰ) the spectral luminosity η (lumens per radiated watt) and (ⅱ) the efficiency of electrical-to-visible conversion. The spectral luminosity, chromaticity, and color rendering index (CRI) are completely determined by the emitted spectral power distribution in the wavelength range 390-750 nm, and hence can be investigated without reference to whether the light source is fluorescent, metal halide, or solid-state. There is a fundamental tradeoff between luminosity and CRI, so a common approach, used here and elsewhere, is to fix the chromaticity of the spectrum, choose a value (or range of values) for CRI, and then iteratively improve the spectrum to maximize its luminosity within these constraints. While many connections have been made between luminosity and various human performance measures, the link between CRI and visual performance is much less certain. Here spectra are optimized first for luminosity and CRI, and also for an alternative set of performance measures: brightness and color gamut. These alternate measures are not proposed as superior to luminosity and CRI, but rather are taken to be reasonable alternatives for the purpose of testing the conclusions reached based on spectra optimized for luminosity and CRI.