Before there was artificial light, the world was a dark and scary place. Half the time, we had no idea what was going on around us! Particularly, that part of the day when the weather turns dark and the sun abandons us to the cold and the moon and stars. People didn’t used to say, “Gee, I can’t wait until tonight, when my pants will get scared off and then my butt freezes.”
I reckon artificial light has been one of the greatest inventions of all times. So what sort of magic is this light stuff, and how do you make it?
To learn how to make artificial light we have to know what light really is. We’re familiar with the fact that white light is actually composed of the complete rainbow of primary colours. These are the different wavelengths of electromagnetic radiation – waves of electrical fields – that we can see.
What we must also realize is that the colour spectrum is only a very tiny sliver of a much, much larger spectrum of electromagnetic radiation, from radio waves the size of the solar system to gamma rays smaller than an atom. Making light means making electromagnetic waves. One does this by shaking an electrical field, or something that has an electrical charge on it.
We routinely make oscillators from electronic circuits that generate e/m waves in the radio and microwave parts of the spectrum (in this sense Marconi and Hertz were making a form of artificial light, but it just wasn’t visible). However we do not have the technology to make an oscillator circuit that can reach the speeds necessary to generate visible light. So we use naturally occurring oscillators and let them do the work for us.
A candle flame, for example, shakes electrons in a way that makes them shed energy as they fall from excited energy states to lower ones as the chemical reaction of oxidizing the fuel proceeds.
But it’s not very efficient.
Although blackbody radiation was not fully explained until 1900, the phenomenon was known for a hundred years before then. Light Bulbs in History:1802 Sir Humphrey Davy1825 James Lindsay, Dundee Scotland, bright enough to read by.1840 Warren de la Rue, England1841 Frederick de Moyelns, England, first patent, using platinum wire.1845 John Starr, USA, patent using carbon filaments1851 Jean Eugene Robert-Houdin, lighted his entire house in France with his own lightbulbs1872, Russia weighs in with its own version, claiming of course to be first and last. As Russians tend to do.
Incandescence works because any hot object radiates light in a spectrum dictated by the temperature and this graph.
If something is hot enough, part of its radiation overlaps our visible part of the spectrum, and we can see it. But a lot of it is invisible. The hotter the object, the more visible light it produces. But most things available to us will melt and even vaporize when they get too hot. Light bulbs are a trade-off between brightness, efficiency, and longevity. And there are a few tricks you can use to make the filaments last longer.
So, who came up with this “bright” idea?
Him? Not even close.
Sir Humphrey Davy, 1802
First patent: England, 1841
What did he have that the others lacked?
A business plan.
Where does Edison come in? 1879 or thereabouts, “Improvement to electric lighting” patent comes after some 30 odd patents on various lightbulbs already granted. What his real contribution was devising a bulb that works well with a distributed electrical supply (his own electric company of course) and making them so affordable that they would dominate the market. In his words, “We’ll make electric lighting so cheap that only rich people will use candles.”
Halogen: slightly better efficiency by upping the temperature, thus getting more visible light for your money from the blackbody spectrum. How? Use special gases in the bulb to keep the filament from vaporizing. And, quartz glass is needed to withstand the much higher temperatures.
Fluorescent lighting started out as “useless” science experiments on the electrical properties of gases such as mercury vapor. The ultraviolet light it produces became a useful tool for scientific research (and a cool party trick). You can also hunt scorpions with it and disinfect things.
It was quickly noticed that UV light can cause some materials to glow in the dark. Finally, someone twigged to the idea of using these glowing materials to actually see by, and making them glow by bathing them with intense UV radiation such as that found inside of a gas discharge tube! Bit by bit fluorescent lights came together until about 1929 they were a commercially and economically viable product.
The UV light created by electrical discharge inside the mercury vapor gets absorbed by the phosphor in the coating (and other glowing stuff), and re-radiated as longer wavelength light at various wavelengths determined by the exact makeup of the coating. The light composition can be fine-tuned to reproduce a desired light effect such as cool light, soft light or daylight. Each type of glowing chemical makes a different color light, and by combining several (usually 4 or 5), you can approximate white light. But it is only an approximation.
How can you tell the difference? Use a CD or DVD. If you see distinct color bands, it’s a fluoro. This is why fine art, people’s skin, plants and other richly or subtly colored objects can look absolutely terrible under fluorescent lighting. The light doesn’t contain all the colors needed to fully represent the object.
Because all of the light coming out is visible light, unlike an incandescent bulb, the efficiency is much higher. Some energy is discarded by the coating as heat. Some energy is consumed by the circuitry needed to ignite and maintain the gas discharge arc within the glass tube. Some light is reabsorbed by the coating because it is not totally transparent, and not all photons are headed outwards in the right direction. In all, fluoros are approx. 5 times better than incandescent bulbs.Still room for improvement?Has anyone heard anything negative about fluoros? At the moment they are very “in.” What about mercury? 5 years’ worth of incandescent bulb usage causes a coal plant to emit (directly into the atmosphere) twice the mercury than is contained in a fluorescent bulb of the same light intensity. CFL’s outlast bulbs by at least 5 times and in some cases 20 times. Therefore flouros put less mercury into the environment than incandescent lights, even IF they are not disposed of properly in mercury recovery facilities.
LEDs: solid state lights. No gas inside a fragile glass tube, no vacuum, no liquids, no filament gradually evaporating to nothing. Only solid crystalline material that can last up to 100,000 hours of use. Uses semiconducting materials to create a specific wavelength of light, depending on how two adjoining semiconductors are “doped” with impurities to manipulate the energy bands of the materials. Invented in 1920’s, not commercially available until mid 1960’s. No blue LED’s until 1993 (available on market from about 1995)
When the achievement of a blue LED was finally announced in 1993, it was a long-awaited breakthrough. Besides looking really cool, blue LEDs combined with red and green ones can make multi-colour lighted displays possible, and for the first time, white light as well.
Some clever person figured out that what works for fluorescent tubes can work for blue LEDs too. A variety of phosphorescent particles are added to the body of a blue LED. These particles absorb some of the blue light and re-emit colours over the rest of the visible spectrum, resulting in white light (though with a certain bluish tinge). Most white LEDs in use are of the phosphor-particle type and not the composite RGB type.
Who can say what the future of artificial light will hold? Will lighting become obsolete due to orbiting mirrors that bathe the earth in sunlight 24 hours a day? Will computer vision and virtual reality make lighting an entire room unnecessary? Or will solid-state lighting finally catch up to fluorescent lights in terms of efficiency and cost-effectiveness?
One thing for certain is that Thomas Edison’s prediction has come true: “(electric lights) will be so cheap that only the rich will burn candles.”