When shopping for lightbulbs in the past, the choices were based on the number of watts, given the belief that the higher the wattage, the brighter the bulb.
Now with the growth of LED energy efficient lighting options, watts are no longer an indication of how bright a light actually is. So, how do we measure that now?
Cue the old lumen measurement of lighting. The lumen measurement has been around since the 1920’s. Its history of measuring light goes back to the “candela” or the light emitted by one candle.
What is the lumen measure of lighting?
The lumen measurement indicates the amount of light you get from a bulb. The higher the number of lumens, the brighter the lightbulb. The lower the lumens, the dimmer the light is.
However, when it comes to energy efficient lighting options like LEDs, lumen isn’t necessarily an accurate indicator of brightness, and given some further consideration, one of the top lighting scientists recently declared that the lumen system of measurement should be reconsidered and replaced.
Should the lumen measure of light be reconsidered?
Dr. Christopher Cuttle, lecturer in Advanced Lighting Design at the Queensland University of Technology in Brisbane, Australia claims in his article, “A changed understanding of light and lighting”, that the lumen should no longer be the single-defining factor in determining brightness.
According to Cuttle, the lumen is purely a measure of visible light. It doesn’t take into account the effect of non-visual impacts, including your body’s natural circadian rhythms. Lighting measurements should consider human responsiveness such as alertness and sleep cycle.
The lumen measurement is based on total quality of visible light emitted by a source per unit of time. The brightness response is for a small light field, but it doesn’t represent all the effects on your eye or brain.
The special distribution of LED lighting brings forth a need to account for the sensitivities of the human eye. In order to convert a light source to lumens, the wavelength reading of the light is multiplied by your eye’s sensitivity to each of those wavelengths.
LEDs are capable of emitting light evenly across your visible spectrum, so they’re brighter than existing industry measures suggest.
How should light be measured instead?
Rather than using lumens, Cuttle suggests measuring lamp and luminaire performance in terms of spectral power distribution in Watts per nanometre.
Spectral power distribution measurement represents the radiant power emitted by a light source at each wavelength in the visible region of the electromagnetic spectrum. It’s used to describe not only light sources, but also illuminants.
Light source is the actual physical entity, whereas illuminants include other sets of values that incorporate the apparent color of an object, described by the reflected light from an illuminated surface or various phases of daylight. An object may appear differently because of different light illuminations.
Cuttle suggests that…
“These proposed changes would enable lighting practitioners to evaluate illumination according to the purposes it is to serve as well as putting them in the role of delivering the range of benefits that advanced lighting technology offers to the community.”