While there has been many studies regarding the impact of lighting on our circadian rhythms, the novel study detailed in the Journal of Biological Rhythms under the title “ Effect of White Light Devoid of “Cyan” Spectrum Radiation on Night-time Melatonin Suppression Over a 1-h Exposure Duration” investigated precisely the impact of white light brightness, with and without the blue spectral component.
The researchers first exposed participants in the evening to lights of various brightness, ranging from dim (under 5 lux at eye level), to 800 lux from a 3000 K light source and 800 lux from a 3000 K, “cyan-gap” modified 3000 K light source (devoid of wavelengths around 480nm). This was done over the course of three weeks, one hour at a time. Later they repeated the experiment with the same subjects, but with light levels reduced to 400 lux at eye level.
Currently, a number of LED manufacturers design white lights with a blue-gap in the spectrum and market them as sleep-friendly on the assumption that the lack of blue light would reduce the stimulation of the melanopsin-containing photoreceptor and hence would suppress melatonin less than a conventional 3000 K light source.
What the researchers report in their paper is that among the 16 adult participants, contrary to their predictions, there were no significant interactions with spectrum, the main impacting factor on melatonin suppression was the light level or brightness and exposure duration.
They conclude in their paper that short-term exposures of about an hour to “cyan-gap” light sources suppressed melatonin similarly to conventional light sources of the same CCT and photopic illuminance at the eyes. More simply said, in order to sleep well, night time ought to be just that, night time.
Lighting Research Center - www.lrc.rpi.edu