Elderly people who find it difficult to sleep may benefit from new glasses that shine blue light into the eyes.
Scientists at the Rensselaer Polytechnic Institute in New York trialled the glasses in a study reported in Chronobiology International.
The glasses give off a blue light into the back of the eyes, but wearers still see as normal.
Volunteers who were exposed to a low level of light experienced a 35 per cent fall in levels of the sleep regulating hormone melatonin, while those with higher exposures had their melatonin drop by 60 per cent.
Low levels of melatonin reduce drowsiness.
Elderly people often have trouble sleeping or being alert during the day because they do not get enough natural light to regulate their melatonin properly.
This is partly from being indoors and also because lenses in the eyes thicken with age, restricting the entry of light.
Produced by the pineal gland in the base of the brain, melatonin is involved in circadian rhythm, or the natural body clock.
by Adrian Galbreth