Wednesday, 29 May 2013

LED lighting for health

It has come to my attention, through my consulting work, that about a quarter of households use significant electricity for lighting even in the middle of the day, when sunlight is free. Perhaps this should not be such a surprise as big windows do lose a lot of heat even with double glazing (though triple glazing is very good). Artificial lighting styles are surprisingly different across cultures. In Japan, fluorescent lighting is preferred in living rooms because incandescents are not bright enough - the Japanese like them for the evening, or for hotels and restaurants [1]. This is very reasonable when you consider the health benefits of strong light (preferably daylight, i.e. 'cool' light  including a bit of blue) during the day. It helps to regularise our sleep patterns and can even reduce symptoms of dementia [2]. However, such bright lights are not good for us in the evening when they can contribute to insomnia, so much so that NASA are testing colour changing lights on the space station to help the astronauts sleep [3].

Hall of Mirrors at Versailles from
In the days before electricity, when we used rush lights, candles and oil lamps, light was never bright enough. Wealthy people used shiny silver, crystal and mirrors to make the most of what there was, reflecting as much light as possible into the room. Taken to extremes, as in the Hall of Mirrors in Versailles it takes my breath away (though I would not give house room to anything so bling).

After the invention of electricity and the incandescent lamp brightness was not a problem and we found a new way to fill our homes with splendour for a range of tastes by covering up the bulbs with shades of different colours. Here is one from Chanel. The dark shade hardly lets any light through and in any case incandescents are not blue enough to help with sleep patterns. However, that is OK because these lights are meant to set a relaxed mood for the evening.

Silk lamp shade from Chanel

Colour temperature
We think of incandescents as producing a 'warm' light whereas fluorescents and LEDs are 'cold', but in terms or colour temperature, the opposite is true: incandescents are 'only' 3000K or so whereas fluorescents are usually 3500K or above and daylight is 6000K. If you think about heating up a steel bar, first it glows red and then as it gets hotter it emits more light at short wavelengths and the mix is white. Daylight is very white and includes lots of blue [5].

Now we have LEDs we can have any colour light we like. There are bulbs available which are 'warm' white or 'cool' white or even switchable between the two such as the Aurora Paragon. That one is pricy but you can get the same functionality more cheaply as an LED strip. You can even get a program for your computer or phone which changes the colour of the display according to the time of day. This means we can have lighting which we can adjust through the day to help our sleep patterns and alertness - though I still recommend making use of daylight wherever possible as it saves energy too.

You can even get RGB bulbs allowing you to select all the colours of the rainbow and cycle through different patterns. There is a public lavatory in Cambridge which does this. However, I can't help feeling there are better ways to make use of the colour changing capability of LEDs. Even the hall in Versailles was more elegant than this.
Parker's Piece toilets Cambridge 04
By Andrew Dunn (Andrew Dunn) [CC-BY-SA-2.0 ( or CC-BY-SA-2.0 (], via Wikimedia Commons

[1] Harold Wilhite, 1996, A cross-cultural analysis of household energy use behaviour in Japan and Norway, Energy Policy
[2] Nicholas Hanford and Mariana Figueiro(2013) Light Therapy and Alzheimer’s Disease and Related Dementia: Past, Present, and Future
[3] NASA to test space-sleep colour changing lights (BBC)
[4] F.lux - better lighting for your computer.
[5] Colour temperature (

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