Why it’s important to turn the lights down low in the evening

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Adequate length and depth of sleep appears to be important for optimal wellbeing and general health. The factors that affect sleep are many and varied, but centre stage here is the hormone melatonin, which is secreted by a structure called the pineal gland in the brain and essentially puts us to sleep at night (and keeps us asleep too).

Melatonin secretion is suppressed by light, but the pineal gland (in health) ramps up its production of this hormone in the dark. In essence, melatonin ‘comes out at night’ to put us to sleep. Any disruption in melatonin secretion therefore may have important implications for the quality and quantity of our sleep, and this may impact on our health in time too.

Bearing in mind that light suppresses melatonin secretion, I suppose we shouldn’t be too surprised to learn the results of a recently-published study that found just this. In this study, individuals were exposed to relatively bright light (200 lux, with lux being a unit of intensity of light) or low light (3 lux) for 8 hours prior to bed time. Those explosed to the brighter light experienced delayed melatonin secretion at night, and secreted melatonin for a shorter period overall too (melatonin secretion was reduced by 90 minutes).

These findings have particular relevance for those of us who inhabit spaces prior to sleep which are light-filled. The authors of the study commented “…chronically exposing oneself to electrical lighting in the late evening disrupts melatonin signaling and could therefore potentially impact sleep, thermoregulation, blood pressure, and glucose homeostasis.” The last point is a reference to the fact that impaired sleep induces changes in blood sugar control that suggest a tendency to type 2 diabetes.

So, what to do? Well, one thing worth trying is to keep light exposure to a minimum in the hours preceding sleep. Dimmer switches are handy here. I have them on practically every light switch in my home. I, personally, had them installed some time ago because I like the aesthetics of low light in the evening. Now I’m doubly glad I opted for them because, in their own way, the fact that I can dim the lights in the evening may be helping me get the sleep I need.

Another thing worth bearing in mind is that computer screens give off a lot of light (usually). It appears that it is the blue part of the spectrum that is particularly ‘melatonin-suppressive’. There exists a free piece of software which filters out blue light out of computer screens at dusk. I’ve used it for some years now and suspect it’s likely to be doing me some good. You can read more about it and download it here.


1. Gooley JJ, et al. Exposure to room light prior to bedtime suppresses melatonin onset and shortens melatonin duration in humans. J Clin Endocrinol Metab 30 Dec 2010 [Epub ahead of print]

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