I’m too lazy to put up Christmas lights, but my neighbour seems to use enough for the whole block. This had me wondering about LEDs and how they have taken over festive decorations—and all kinds of other things as well.
LED stands for Light Emitting Diode. A diode is a semiconductor with two electrodes: N-type and P-type, for Negative and Positive. A semiconductor can change its ability to conduct electricity. Most semiconductors are poor conductors of electricity. To change the conductivity, another material must be added through a process called doping (which has nothing to do with the Olympics). The material added to the N-type provides extra electrons, which makes it negative, while the material added to the P-type has more “holes,” through which electrons can move, making it positive. This allows electricity to flow in only one direction.
When electrons go from a high-energy state to a lower one, they give off energy in the form of photons. Diodes generally give off some form of electromagnetic radiation (which includes light) as a by-product of conducting electricity. LEDs are designed to exploit (in a nice way) the light produced.
A lone LED usually produces a single wavelength of light, which is dependent on the material used. The wavelengths produced can range from infrared, used in remote controls, to the visible spectrum used in Christmas lights, to ultraviolet light used to harden nail polish.
Early on, red and green LEDs were created to use as function indicators. However, blue light (not the beer) required a higher charge in electron energy and that made the technology more difficult to develop. After the breakthrough discovery, that led to a Nobel prize in physics, white light could finally be created using blue light and different phosphors. Since then, applications for LEDs has exploded.
Another important factor in the spread of LED technology has been the decrease in their price. The price of LED lightbulbs still seems high, but compared to incandescent bulbs, they generate much less heat and are therefore much more energy efficient. They also last much longer. The significance of LEDs to lighting technology has been compared to the era when transistors took over from vacuum tubes (if that means anything to you).
On the downside, astronauts have documented that some of the cities that adopted LED streetlights have increased light pollution. LEDs tend to emit more blue light, which can travel farther than other wavelengths of visible light. Combined with a poor lighting design, this has resulted in a loss of darkness.
Although the dark side tends to get a bad rap in popular culture, light pollution is not simply a nuisance to stargazers. It can impair human sleep habits and disrupt the behaviour of nocturnal animals, among other concerns. So, although LEDs have the potential to shine a path to a brighter future, we need to keep an eye out for dim-witted consequences and seek more enlightened strategies for using them.