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

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]

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

  1. Anne Robertson 15 January 2011 at 1:24 am #

    Blind people with no light perception such as me often suffer from severely disrupted sleep patterns. I seem to want to get my sleep in two sessions: a longer one at night, say four or five hours, and a shorter one in the afternoon of around two hours. This gave me endless trouble when working normal office hours and in those days, no one had done the research on melatonin so I just felt guilty and inadequate.

  2. Peter Andrews 15 January 2011 at 1:31 am #

    Just by coincidence, the same day I read your post I read this blog post suggesting we are likely to increase indoor lighting a lot as the cost of lighting comes down: http://www.overcomingbias.com/2011/01/the-future-is-bright.html

  3. Susan 15 January 2011 at 2:08 am #

    What about the link between lack of daylight and depression in winter though? Seems contradictory to me?

  4. gill oliver 15 January 2011 at 6:17 pm #

    what a coincidence, i started reading in bed this week with a kindle device which gives out the same kind of light as a computer, the very same night i was unable to go to sleep for several hours, i never have any electronic devices in the bedroom as i am a great believer that the bedroom should be used for sleeping in only.I shall be returning to books in the future whilst in bed.

  5. Richard 16 January 2011 at 3:41 pm #

    Hi Susan

    I think it is important to get the right quality and amount of light, at the right time. I read somewhere that to help avoid SAD we should get 1 hour of daylight at least 3 times per week, preferably in the morning or at lunchtime. I aim to get out at lunchtime most days.

    Also, as touched on by John, the blueish light in the morning helps stimulate us, while the warmer redder light in the evening signals to us it is time to wind down. Candles are nice in the evening and if you get up in the night for the bathroom you can leave a very dim child’s night light on in your hall, to avoid shocking bright light.

    Lastly you may all be interested to learn about the Lighter Later a campaign by 10:10 to change the clocks to cut CO2 emissions and that may increase our wellbeing: http://www.lighterlater.org/

  6. Michael 21 January 2011 at 5:18 pm #

    @ Gill Oliver

    The kindle emits no light at all. It certainly does not give “out the same kind of light as a computer”.

    So whilst your kindle reading may have been responsible for your being unable to sleep (a scary story perhaps?) it cannot be the light given off by the kindle that kept you awake, as it does not give off any light.

    I have a kindle and it is almost exactly like reading a book. I have found my sleep is better since getting one, partly because I watch less television (which gives off blue light) and use my computer less in the evening because I read more.

  7. TP 23 October 2011 at 12:31 pm #

    Hi John,
    I’ve just found this article after a relaxed morning browsing your archives. It made me smile because, due to an electrical fault in our flat, our evenings are mostly lit by candles! Given that anecdotally, dimmer switches use more energy than standard switches, and that Morrisions sell a pack of dinner candles for £2.50, we have found candlelight a great way to make our evenings cheaper and more relaxing… And now, potentially health-improving!


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