Alzheimer's' Disease

The common thread in many research papers is that the organic progress of Alzheimer's Disease results in damage to a part of the brain (the Suprachiasmatic Nucleus or SCN) that controls circadian rhythms.

By using bright light, disruption to the normal circadian rhythms can be reduced, making it more likely that the patient will be able to fit in with a normal daily sleep/wake cycle.

The combination of damaged nerve pathways caused by Alzheimer’s Disease and gradual deterioration of the eyes due to ageing, means that indoor levels of light are not usually sufficient to signal that it is daytime, so the patient’s internal body clock is not attuned to the usual daily pattern. This affects not only the wake-up processes at the beginning of the day but also the rest and sleep cycle that come into force in the evening.

"Sometimes the ability to control [sleep disturbance] can make the difference between keeping a loved one at home or in an institution. Too often we shut people with dementia up in dark rooms, with little opportunity to see the sun or other bright light, which can make their symptoms worse."

Effect of light on agitation in institutionalized patients with severe Alzheimer disease.
Am J Geriatric Psychiatry
Ancoli-Israel S, Martin JL, Gehrman P, Shochat T, Corey-Bloom J, Marler M, Nolan S, Levi L.
patients with mild or moderate AD, might benefit from light treatment even more than those with severe AD.

Several studies more using bright light again find positive results for Alzheimer's patients

Light Therapy used in the treatment of Parkinson's disease