A first, I suppose

One of the technological stories lurking in the background is that LED lighting is going to become much more common soon. LEDs now can come in any colour, and they are potentially more efficient and give off much less heat than conventional incandescent light bulbs. (As to how they will compare with fluorescents, well we shall wait and see).

So here it is: a fully LED lit apartment. We may all go there one day. For now, I am slightly worried about the purple (although I am sure they would call it "violet").

Update: I don't know why they went with all the purple, actually, given that it is not especially difficult to get white light from LEDs these days. (That said, LED white looks a little strange to people used to fluorescent or incandescent white, because the mix of colours going into the light is a little different).

The story behind this is that until the early 1990s, it was essentially impossible to make an LED that could generate blue light. LEDs up to then were mostly made from Gallium Arsenide, but there are phsical limits as to just how short the band gap and hence the wavelegth of the light can be made using this material. What this means is that using Gallium Arsenide you can make infra-red, red, orange, yellow and green LEDs, but not blue ones. If you are going to produce white light, you need blue. In the early 1990s an engineer name Shuji Nakamura, from a company called Nichia Chemical based on the Japanese island of Shikoku, figured out how to produce blue, violet and ulta-violet LEDs made from Gallium Nitride. This meant that LEDs can be made any visible colour and also can be made to produce white light, either by using red, green and blue LEDs together, or by using a phosphor coating around a blue LED to reduce the energy (and hence change the colour) of some of the light, which will then mix with the blue to form white. (Blue has higher energy than either red or green, so it is possible to make red or green from blue by taking some of the energy out, essentially. It is not possible to turn red or green into blue by putting more energy in, however).

LEDs have a number of potential advantages: they are light, tough, and potentially more efficient than conventional lights (although we are not quite there yet). However, making LEDs was (and is) still quite expensive compared to making incandescent or fluorescent lights (and there are one or two other issues that I won't go into right now) which is why LEDs haven't completely taken over the lighting business just yet. However, they have found their way into certain niche markets such as traffic lights, and lights used on bicycles and for other outdoor sports. Most people believe they will take out a lot of the rest of the market before too long though.

(Another niche application is giant scoreboards in sporting arenas and other large outdoor screens. You may have noticed that the quality of such screens improved dramatically in about 1995. This was because of the invention of the blue LED. Prior to that such big screens had to be made of a large number of small cathode ray tubes, and the pictures were often fuzzy. After the invention of the blue LED, a combination of red green and blue LEDs could be used to make the pixels, and these big screens suddenly produced much sharper and brighter pictures).

Another place to look for LEDs like this is in pixelated displays giving departure times in railway stations and bus shelters and the like. Older such displays will always be yellow or red. Newer ones may also contain blue or even white. Huge numbers of red and orange displays is one of the things you remember about travelling on trains in Japan, as they took to these displays in a big way early. (That said, even newer ones are often still red or orange. Force of habit, I guess. That and the fact that red and orange LEDs are still cheaper and more efficient).