The relationship between light and human health was called to the nation's attention almost five years ago by the National Lighting Bureau, when the Bureau reported on the then-recent discovery of nonvisual photosensitive ganglion cells in the human retina. Not used for seeing, these retinal ganglion cells (RGCs) connect directly from the retina to the suprachiasmatic nucleus (SCN) of the hypothalamus, where the pineal gland is located. The pineal gland secretes melatonin, a hormone that acts somewhat as an anti-oxidant "blood cleaner." Melatonin levels normally build in our blood while we sleep, then drop during the day in response to light. The RGCs explain why the amount of light in a space influences the production of melatonin in people.

Dementia commonly disturbs sleep/wake cycles and also causes deterioration of cognition, mood, and behavioral organization. The 1999-2004 Dutch study looked into these issues by comparing the impact of lighting on a sample comprising 189 residents of 12 assisted-care facilities. The residents - 90% women - averaged 85.8 years of age; 87% had been diagnosed with dementia.

Higher-wattage lamps (light bulbs or tubes) were installed in ceiling fixtures of six facilities. The new lighting produced 1,000 lux, an international measure of illuminance (amount of light) equivalent to 93 foot-candles, or about 50% more than the illuminance commonly found in many open-office areas. In the other six facilities, indoor lighting produced about 300 lux. In all 12 facilities, the lighting was used in what was termed a "whole-day" mode; i.e., from 9AM to 6PM. In addition, one group was given 2.5 mg of melatonin each evening, while another received a placebo. All subjects were randomized to treatment.

According to the report, the 1,000-lux lighting of itself reduced cognitive decline by 5%, symptoms of depression by 19%, and physical functional decline by 53%. While those who took melatonin enjoyed 25% more uninterrupted sleep, melatonin alone tended to aggravate withdrawal and depression. The combination of higher levels of whole-day lighting and melatonin increased sleep efficiency by 3.5%, reduced nocturnal restlessness by 9%, and reduced agitated behavior by 9%.

"Spectacular" was the word Dr. Michael Hastings used to characterize the study's findings. A noted British researcher into circadian rhythms and Alzheimer's disease, Dr. Hastings was quoted by BBC News as saying, "Although 5% may not sound like a huge amount, it compares well with treatments such as Aricept designed to slow the progression of the illness. Over the course of Alzheimer's, it could represent six months, and you have to remember that the light therapy is completely noninvasive, and melatonin is a very gentle drug." Dr. Hastings added that sleep disturbances often comprised the "final straw" for relatives trying to care for loved ones with dementia. "You can have a situation where someone is asleep for part of the day, then at 3AM will be awake, wandering around the house, turning the gas on. Relatives can manage quite a few of the symptoms of mild or moderate dementia, but this can be too much. It's a crunch issue, and if someone could be kept at home for an extra six months, rather than placed in a care home, there are huge personal and social benefits."

Writing in the June 10, 2008 issue of Journal Watch Psychiatry, Peter Roy-Byrne, M.D. commented, "As the authors note, even the cognitive effects (which were more modest than the physical ones) fell in the range of those reported for cholinesterase inhibitors. Light plus melatonin could improve quality of life in this highly vulnerable population at a modest cost."

Quoted in the June 10, 2008 issue of Time, one of the study's authors - Eus Van Someren at the Netherlands Institute for Neuroscience - said, "I had expected, based on previous studies, that we would find improvements in sleep. But I hadn't expected to see the effect on cognition." Van Someren also noted that, because the cognitive gains were about the same that Alzheimer's patients achieve by taking cholinesterase inhibitors, "...it may make sense for people to consider living in a better-lit environment."

Lighting-level recommendations, such as those published by the Illuminating Engineering Society of North America (IESNA) or the International Commission on Illumination (CIE), usually are based on "visual performance" or how quickly and accurately the eye sees visual tasks. However, those who develop lighting recommendations are, increasingly, considering the human-health aspects of light. Lighting designers concerned about lighting quality, energy use, and the creation of "green" facilities are innovating designs that use high-efficiency light sources, combinations of daylighting and electric lighting, plus control systems that help balance and control energy use.