Sun 10 Aug 2008
We recently had a new bathroom fitted and as it is an internal room lighting is important. When we first moved, in the old bathroom gave a good impression of the Black Hole of Calcutta (well more like the green and blue hole of Calcutta, an interesting colour scheme), lit by a single 40w tungsten bulb. On the first day, all the old tungsten bulbs where removed and replaced with modern low energy bulbs. In the bathroom I put in a 14w, which has a light output equivalent to a 75w tungsten bulb, a considerable improvement straight away.
Putting in a new bathroom gave the opportunity to make more radical changes. My first thought was to use halogen down lighters and flood the room with light, however there are a few issue with halogen down lighters. First off, care must been taken when fitting them into an existing ceiling, as they can be a fire risk due to the heat they generate. Secondly, all that heat is just wasted energy, with most of the energy being converted into heat rather than light. As halogen bulbs are not the most efficient means of lighting, the search was on for energy efficient replacements for the standard GU10 halogen bulb.
Most people are now aware of low energy (compact fluorescent lamps or CFL) bulbs, even if not everybody is using them. There are now CFLs which can be used to replace the old fashioned tungsten GU10 bulbs (GU10 refers to the type of fitting). They are at the present time more expensive (£5 to £6 per bulb) than the halogens they replace (£0.79 per bulb), but the CFs use less energy and last longer, but more on that later.
However I wasn’t convinced this was the most energy efficient solution. Through my interest in cycling I knew that in high end cycle lights halogen bulbs have now been entirely replaced by LED lights. Indeed the popularity of 24 hour cycle racing, where the race continues through the night (at the extreme is the Strathpuffer with 17 hours of darkness), have helped to drive development in this area, as bright and energy efficient lights are important to this sport. If you are hurtling down a forest track in the dark, you want plenty of light to find your way. Yet at the same time you don’t want to be lugging a heavy battery about, so low energy consumption is essential. The German light makers Lupine show just what can be done with their Betty 14, a 1500 lumen 22w light which can run for 6 hours on a 14.5 Ah Li-Ion bottle battery. The whole setup only weighs 810g. Ok, so it comes at a price (£685.00, just in cast you want to know what I would like for Christmas) and 1500 lumen is way more brightness that the average domestic lighting system would use, but has any of this high end technology filtered its way down to the domestic lighting market?
Well yes it has, you can get LED lights as replacements for halogen bulbs, but there are a few differences in what is required from a bike light compared with domestic room lighting. As stated above, top end bike lights are far brighter than domestic lighting systems, also there is the colour of the light to be taken into account. As light colour and temperature can be a wee bit confusing, here is a short digression into light colour/temperature.
A lighting designer will describe white light as being cold or warm depending on whether it is towards the yellow end of the spectrum or the blue end, with yellow being warm and blue cold. On the other hand, a lighting engineer will describe white light according to its temperature in degrees Kelvin (°K), to them a “warm white” light has a temperature of 2700°K and the “cold white” a temperature of 5000°K. So why the difference? The designer gives a subjective description of the light, and we have become accustomed to the yellowish white light of the tungsten bulb in most domestic lighting situations. Before that we would have experienced the light of oil lamps or candles, which have a similar coloured light. This light is described as being warm. Whereas white light which is to the blue end of the spectrum, and is closer in colour to that of daylight, is regarded as harsh and cold. The engineer on the other hand describes light according to the level of energy required to generate it. For millennia metal workers have known that if you heat a piece of metal it will start to glow, at first red, then as you heat further straw yellow and eventually it will become white hot. At this point metals start to melt, and if you are using arc welding gear to melt the metal, you will notice that the electrical sparks give out a blue light as they are hotter still. The temperatures at which these colours are produced can be measured, hence colour temperature is given in °K. Ok so back to the subject at hand.
Most bike lights produce a “cold” white light with a temperature of about 5000°K, this is often considered too harsh and cold for use in a living area. So for domestic use there are GU10 LED lights which can replace the bog standard halogen down lighter, these usually come as a choice of either warm white (3200°K) or cool light (5000°K). Power usage ranges from 1w to 4.3w and their light output can be equivalent to 35w to 50w halogen blubs (specifications can vary between manufactures). As this is in many ways still a cutting edge technology, prices are on the high side at between £6 and £18 a bulb.
So to the big question, is it worth spending £18 on a bulb when you can get a halogen bulb for £0.79 to do the same thing? The answer depends on the time scale you look at and how much you use it, to find out it is necessary to carry out a little economic analysis. To do this I, have developed a simple tool which you can access here.
Basically halogens are cheap to buy but use a lot of expensive energy and have a short lifespan (typically about 2000 hrs). Whereas LEDs are expensive to buy, but use very little energy and have a very long lifespan (typically about 50000 hrs), CFLs are somewhere in between. To see which is the better value in the longer term I chose the following scenario, using four bulb fitting, for four hours a day (OK so that is a wee bit longer that we normally use the bathroom per day) using electricity at a costing of £0.18 per kWh (a rate taken from an old bill, before the recent price hike!), what would be the total running cost per year? In the first year the total cast halogens would be £39.10, using CFLs would be £12.96 and using LEDs would be £4.90. This suggest that saving in energy costs of using the LEDs would repay the capital investment is a little over two years. However at the current time the cost of energy is going up and the cost LEDs is coming down, so this could soon be even shorter!
Edinburgh
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