Are ganglion cells more sensitive to certain colours?

Russell - We've shown in both mice and humans that it's at 480nm, the blue part of the spectrum. You can imagine it as a bell-shaped curve with a peak being at 480nm in the blue part of the spectrum. But it's worth saying that we originally discovered these cells because we were looking at how the clock is regulated by light. But actually, what these cells are doing is plugged into a whole raft of different brain structures in the hypothalamus and the thalamus, and they're regulating lots of brightness detection tasks generally. These are not just clock regulators. So for example, part of our pupil constriction in response to bright light is via these photosensitive ganglion cells, again, blue light sensitive. Part of our arousal systems and part of our sleep systems are all being regulated by these extraordinary cells.

Ben - Different types of light bulb give out different ranges of light. What about when we're using energy saving light bulbs which give out these very distinct bands of radiation? If that doesn't happen to coincide with the blue that we need to set our day, then does that mean that all of these energy saving light bulbs might actually be disrupting us?

Russell - Well it raises a really very interesting issue because what you want to do is fine-tune artificial lighting systems to enhance reading at certain times, but also, you want to either stimulate these photosensitive ganglion cells, increase alertness let's say, or not stimulate them at night when you want to go to sleep. So, there's increasing attention being paid to fine-tune artificial light sources to stimulate both the visual system versus this photosensitive ganglion cells.