Researchers at the Surrey Sleep Research Centre at the University of Surrey found that the ordinary, artificial indoor-light we are exposed to in the evening suppresses the rise of melatonin, making us feel less sleepy, and thus more inclined to delay bedtime. This is because most lights contain a high amount of blue light; however the researchers found that when they altered the colour of light, reducing blue light and increasing the red and yellow, the disruptive effects of the light were minimised. (Luc Schlangen, Nayantara Santhi, Derk-Jan Dijk, Journal of Pineal Research Nov. 2011).