Biologically Relevant Lighting: An Industry Perspective

Abstract

Innovations in LED lighting technology have led to tremendous adoption rates and vastly improved the metrics by which they are traditionally evaluated-including color quality, longevity, and energy efficiency to name a few. Additionally, scientific insight has broadened with respect to the biological impact of light, specifically our circadian rhythm. Indoor electric lighting, despite its many attributes, fails to specifically address the biological responses to light. Traditional electric lighting environments are biologically too dim during the day, too bright at night, and with many people spending much of their lives in these environments, it can lead to circadian dysfunction. The lighting industry's biological solution has been to create bluer days and yellower nights, but the technology created to do so caters primarily to the cones. A better call to action is to provide biologically brighter days and biologically darker nights within the built environment. However, current lighting design practices have specified the comfort and utility of electric light. Brighter intensity during the day can often be uncomfortable or glary, and reduced light intensity at night may compromise visual comfort and safety, both of which will affect user compliance. No single lighting solution will effectively create biologically brighter days and biologically darker nights, but rather a variety of parameters need to be considered. This paper discusses the contributions of spectral power distribution, hue or color temperature, spatial distribution, as well as architectural geometry and surface reflectivity, to achieve biologically relevant lighting.

Keywords: Opn4; circadian; lighting; melanopsin; social jet lag.

FIGURE 1

Nine spectral metamers of light, each with different blue light peaks. 410 nm peaked metamer (purple), 420 nm peaked metamer (green), 430 nm peaked metamer (yellow), 440 nm peaked metamer (red), 450 nm peaked metamer (royal blue), 460 nm peaked metamer (orange), 470 nm peaked metamer (black), 480 nm peaked metamer (gray thick), and 490 nm peaked metamer (sky blue) are overlayed on top of tristimulus color matching functions X (gray–long dash), Y (gray–dash dot), and Z (gray–small dash) according to CIE1931, as well as melanopsin sensitivity function (gray–solid) according to CIE S 026. Each metamer produces visually the same 4,000 K color of light at the same lumens according to the tristimulus functions.

FIGURE 2

Melanopic daylight efficiency ratio (DER) of the nine 4,000 K spectral metamers from Figure 1 organized by their peak blue emission on the X-axis (410–490 nm).