At the core of ‘circadian lighting’ is the phenomenon that we call ‘the melanopic response’.
This comes from the research that’s been going on into the ‘non-visual’ effects of lighting. It relates to the way that blue frequencies in daylight restrict the production of melatonin in the body’s system until after dusk, after which time melatonin washes through the system – and it’s time for bed.
The lighting industry is interested in producing the most efficient ‘blue light’ component in order to promote artificial lighting systems that can mimic the effect of daylight.
The frequency at which the melanopic response is most efficient is 480nm (or 490nm according to others). LED lighting systems are in production that concentrate the ‘blue pump’ of the visual spectrum at this wavelength, the idea being that energy can be saved by concentrating the spectral distribution of the LED at those frequencies where there is a known physiological reaction.
There is a new metric for measuring this kind of light. This is the Equivalent Melanopic Lux (EML). It is measured 1.2m above the floor (assumed eyelevel for a desk-based worker), and its measured vertically. We’re familiar with horizontal illuminance requirements on the working plane, but there is no straight-line conversion between the vertical and horizontal. The amount of light on the vertical plane will depend entirely on the way that light is delivered into the space, as a combination of direct light from a luminaire, reflected light from walls and ceilings – and perhaps a contribution from windows.
Is this a good idea?
There is a potential contradiction of objectives. On one hand, we are learning how the body’s hormonal systems respond to light and we’re starting to chart the best way to work with light throughout the day to help with pursuing a healthy lifestyle. However, most of these lighting systems are designed to be used during the working day, which doesn’t coincide with the natural summer-winter cycle. These systems are intended to provide an alert working environment, for as long as we’re at work. Beyond that, we’re expected to look out for ourselves. And for shift workers, that can be very difficult.