By Manuel Spitschan
Around 20 years ago, a new type of cell was discovered in the human retina, the fine layer of tissue at the back of our eyes that enables us to see the world in its colourful detail. These cells, the intrinsically photosensitive retinal ganglion cells (ipRGCs), are sensitive to light independent of the canonical photoreceptors, the cones and the rods.
By Brian Liebel
IES Director of Standards and Research
This article is an expanded version the article found in the 50th Anniversary issue of LD+A, July 2021, providing additional background, more references, and personal insights by the author.
By Ian Ashdown, Senior Scientist
SunTracker Technologies Ltd.
Nighttime light pollution is sadly familiar to all of us. While our grandparents and great-grandparents may talk fondly of seeing the Milky Way in their youth, with thousands of stars scattered across the dark summer sky, we are mostly content with seeing a few dozen stars through the never-ending dusk of urban and suburban skies.
It seems that every month there is a new metric proposed to quantify the performance of light sources, particularly with respect to spectral properties. One of the latest examples is Average Spectral Difference (ASD).
By Travis Longcore
From the position of wildlife, the best artificial light at night is no artificial light at night.
By Naomi J. Miller, PNNL; Anne (Lia) Irvin, PNNL
The candela and the lumen are units based on one form of human spectral sensitivity, characterized with the weighting function known as V(λ), which was derived under a very narrow set of experimental conditions by multiple researchers, and the results awkwardly combined in 1924 to produce the familiar photopic response function [Sharpe and others, 2005].
By Mehlika Inanici, Ph.D.
The dynamic intensity and spectra of daylight inform human beings about the passage of time and weather, produce the best color rendition, regulate circadian rhythms in all living beings, and facilitate sustainable lighting practices.
By Sam Berman, HFIES
Senior Scientist Emeritus Lawrence Berkeley National Laboratory
Robert Clear, FIES
Staff Scientist (Retired) Lawrence Berkeley National Laboratory
During the past two decades, the lighting community has come to recognize that retinal photoreception extends beyond rods and cones, and includes a small number of intrinsically photosensitive retinal ganglion cells (ipRGCs) with their own unique spectral sensitivity. In this dialogue we provide a simple method for incorporating the metrological consequences of this sensitivity into lighting practice.
By Eric Bretschneider
For better or for worse, the lighting industry commonly associates the lifetime of LEDs and LED-based lighting products with L70 – the amount of time for the lumen maintenance of an LED-based device to reach 70% of its initial value. Admittedly, the failure of other components, particularly those that provide power to LEDs, are more likely to determine the overall lifetime of an LED-based component or luminaire. However, only lumen maintenance is considered here.
By Christopher Cuttle, MA, PhD, FCIBSE, FIESANZ, FIESNA, FSLL
This procedure is based on the concept that there is real advantage to be gained from changing the illumination metrics used for specifying, measuring and predicting lighting applications so that they relate to people’s responses to visible effects of lighting in indoor applications.