Early temporal isolation studies overlooked the fact that artificial light has an effect on circadian rhythms but more recent research showed that even fairly dim lighting may reset the SCN (suprachiasmatic nucleus). Even more recently research has found that blue light is particularly effective – for good and bad.

The story starts with blind people – some blind have considerable difficulties with their circadian rhythms because their insensitivity to light means that their body rhythms are constantly fluctuating. However, this is not true of all blind people. It seems that the eye has special light receptors related to the circadian rhythm and these feed directly into the SCN (Czeisler et al., 1995). Other research has found that these special cells are particularly sensitive to blue light. For example Kayumov et al. (2005) found that volunteers doing simulated shift work had reduced melatonin production if they were exposed to bright light but not if they wore goggles that filtered out blue light. Dim lighting also did not result in reduced levels of melatonin.

You may ask ‘Where did the melatonin come in’? Light resets the SCN and also suppresses the production of melatonin (when it gets dark, melatonin levels rise making us sleepy). Suppression of melatonin has been linked to cancer, obesity, diabetes and cardiovascular disease. So shiftworkers doing night work with bright lighting are exposed to risks that could be prevented if the lighting was dim or blue light was filtered out. In fact the same is true for all of us, at night it is better to sit in dimly lit rooms and use lighting with less blue in it.