Orange lighting is not as bright, but the sodium rates higher than halide on a foot-candle meter taking lumen readings because it reads light from a different spectrum than our eyes see it. The human eye is more sensitive in lower light levels to the bluer spectrum of light, and adapts, but the current light meter does not adapt to the “S” curve.
In fact, according to the World Institute of Lighting and Development, the parent corporation of Magnaray International Division, manufacturer of high-quality exterior lighting products, lighting practitioners have suspected for years that current lighting metrics don’t actually reflect human perceptions of the full field of view visual acuity. Recent research has identified physiological causes that explain nuances in different lighting installations, challenging current photometric procedures and shortcomings.
Magnaray’s president, Larry Leetzow, calls for the industry to come up with a total light quality metric. Unfortunately, he says, there are no degrees for lighting engineers.
“Meters look at foot-candles per watt, but it’s not the same as actual sight with the human eye, which is sensitive to green during the day and blue at night. Too much blue distorts red and green; you need a source to balance red, green, and blue: white light.”