Let there be light! [1]

After the short enlightenment [sight] posted about what light is, and about it's wavy nature, remains, among others, the neat question of how to produce light. This can sound like a little obvious, but after listing a few ways, I hope it will be clear that every different way opens very interesting possibilities and/or holds complicated downturns. The really only way to hack those characteristics is to understand where they come from, and why are they like this.

The first and obvious source of light to be understood is the sun. The sun is a huge sphere of gas (mostly hydrogen) that reaches high temperatures.

That's it.

We are not going into the details of how and why is it hot (thermonuclear reactions in the core - and that's enough about it for this post). Very hot gas will emit light. As a matter of fact, any other body will radiate light at high temperatures. If you take, for instance, a piece of metal, say, iron, and heat it to 1000° C, it will glow at a reddish/orange color.

A Light Bulb works pretty much this way. It has a tungsten (temperature resistant metal) coil that resist to the electricity that flows through it. By resisting the electricity, it heats up. And, as said, whatever body heats up, will radiate light.

So, here comes the first disadvantage of using such method to create light: reaching high temperatures. High temperatures requires heat insulators and protection from fire, among other problems.


[Picture above: on every temperature (the curves) different distributions of colors. At 4500 Kelvin, most of the energy is concentrated on the infrared side. At 7500 K, most of the light comes from the blue. Interestingly, at 6000 K (temperature on the surface of the sun), the peak is at the yellow. Even if the light from the sun is mostly white, the sun looks yellow to us.]


The second disadvantage comes together with a great advantage. Remember spectrum of light briefly explained before? Well, light emitted from a hot body will come in a wide spectral range. That means: not one single frequency, but a full range of colors. In this situation, the light will look fairly whiter and nicer to the eyes, mostly because our eyes had gone through an evolutionary process over ages that made it very sensible to this kind of illumination. More then this, because since all visible colors are available in more or less the same strength, the illumination will reveal colors much closer to the real color of objects (if you take an apple under blue light, for example, it will look black. If a color is not available in the ambiance, it obviously cannot be reflected by objects, and they will not reveal their true colors).

Well, the disadvantage lies in the fact that most of the energy resides in a region of the spectrum that cannot be seen by the eyes: infra-red. This is not only a huge waste of energy, but also a dangerous one, for infra-red means basically heat. That's why not only light bulbs are hot, but they heat everything around them.



[Picture Above: for comparison from the previous graph, this is how is distributed the light emitted from a "white" led: here the distribution of the light is much less equal over different colors. And this is the reason that under this kind of illumination objects take a very weird color value]