An efficacy analysis of HID lamps

HID lamps have a wide variety of chromaticity, color rendering and luminous efficacy values. It will be shown that these three parameters are closely related to one another. This relationship is demonstrated by analyzing the luminous efficacy in terms of three efficiency factors: 1) Visual efficiency, 2) maximum spectral efficiency and 3) spectral efficiency. It has been observed, in spite of the many differences between high pressure sodium, metal halide, coated mercury and even microwave-driven sulfur lamps, a remarkably linear relationship for these lamp types has been found between the spectral efficiency and CRI. The results presented give, in perspective, the limits of existing HID technologies with respect to color point, CRI and efficacy.