Thursday, February 20, 2014

The future of lighting

For over 100 years, the incandescent light bulb gave light to the masses; cheap, safe light. It was safer than candles and oil lamps and cheaper to run after wiring and so on had been taken into account. Then along came the compact florescent light which slowly usurped the place held by the incandescent light bulb. Legislation was enacted banning the production and use of incandescent bulbs under the guise of environmental friendliness.

Some truths about CFL bulbs are uncomfortable - they contain mercury which the original incandescent bulbs did not. Worse than that, they contain mercury vapor - in fact their original name was the mercury vapor lamp. Suddenly they don't sound so friendly. All the older bulbs could be 100% recycled. The CFL bulbs need to be disposed of in special facilities.

Recently, along came a new kind of light - the white LED. They're still in the early stages but they are available for use in desk lamps and more. The best thing - no mercury and they have a life of about ten years compared to the year of an incandescent bulb or the three years of a mercury vapor bulb. Even better than that, while a 100 watt incandescent bulb will produce around 16 lumens per watt or 1600 lumens, a CFL will produce around 60 lumens per watt. Thus, to get the same lumens as a 100 watt incandescent bulb we only need a 26 watt CFL. People often complain CFLs are dim and they are because 13 watt is the most common variety and that's half the power of a 100 watt incandescent bulb.

Forward a little and along came the breakthrough everybody was waiting for. For years, LEDs had been available solely in red, yellow or green. Suddenly blue became available and with blue came the ability to produce a white LED. That was the breakthrough the world was waiting for.

Forward a little further and now vast banks of LED light panels are available for use in television studios. Gone in large part are the banks of hot and powerful ordinary incandescent bulbs that would from time to time shatter and shower the presenters or actors with broken shards of glass. Not just that benefit but lower power bills and crucially no heat. This is money saved on air-conditioning. LEDs typically produce around 40 lumens per watt.

In my stairwell, I have an LED bulb illuminating the stairs, replacing the CFL that was there originally. It has resulted in a reduction in my monthly electricity bill of around $2, which is very welcome. My desk lamp was designed for a 40 watt incandescent bulb and has a 1.2 watt LED bulb instead with zero heat emitted and less power consumed.

The downside of "white" LED bulbs is that at the moment they're not a universal white. Different batches from different manufacturers can vary from bluish to greenish or yellow through to orange. The more expensive LED lighting arrays tend to be precisely color balanced to within a very few degrees Kelvin.

Now, what has all this got to do with photography? Well, now that you have some background to the development of lighting and how we are now using ever less power and getting ever more light for that power, I can make some predictions and perform some analysis.

In the 1950s, Harold Edgerton produced the world's first electronic flash. This is a simple glass tube filled with argon that has a 300v current passing along the tube, through the argon. This is what produces the flash of light from a flashgun. It's a bit more complicated because argon won't conduct 300v unless it has been ionized with a 3,000v ionization supply. This ionization is provided by 3,000v passing through a wire wrapped around the flash tube. The downside of argon is that it has a residual afterglow and that means that the absolutely fastest pulse of usable light from a flash tube is going to be somewhere in the region of 100,000th of a second. Now that might sound fantastically small until you realize that many industrial processes happen in less time and need to be photographed. As an example, somebody recording ballistics may need to fire a .223 bullet at a sheet of glass to see what happens and when. A .223 bullet can travel at up to 3,000 feet per second. Now you should begin to see the problem. In a hundred thousandth of a second, such a bullet will travel 0.03 of a foot. This is around a third of an inch. That might not sound much but most sheets of glass are an eighth of an inch thick. Did the glass bend before it shattered or did the bullet punch a hole straight through? Was it the impact that shattered the glass or the vibrations caused by a hole being punched through? These questions need a faster flash.

Harold Edgerton also devised a really fast flash called a microflash. There are some ideas on building one in the two books on high-speed photography Book 2 and book 1. Microflashes do not use Argon. Generally they use air which is 78% nitrogen. This means that while Argon produces a nice natural flash that's barely blue, the air flash will have a very heavy ultraviolet element. It also needs some pretty scary voltages. I'm talking about 14,000 volts for the main power (versus 300v of the Argon flash) and 28,000 volts for the ionization supply. Not only are those very scary and very dangerous but they're also quite challenging to achieve and control. The components capable of handling such voltages are hard to obtain. Many are available solely from old Soviet military supplies. Before you start worrying, no - nobody can turn microflashes into a weapon.

So, why am I talking about this? Purely because this is where LEDs come in. The fastest LED can produce a pulse of light of a 2,000,000,000th of a second long. That's right - a two billionth of a second pulse of light. Now you can see why I am so excited. In a two billionth of a second, a bullet traveling at 3,000 feet per second will travel 3/2,000,000th of an inch. That's hardly any movement!
The flash that took this photo was 1/38,000th of a second (described in the books). The bullet was an air-gun pellet traveling at 500 feet per second. The flash was an easily obtainable camera flash and the camera was pretty ordinary too. Now imagine if the flash was a lot faster - the pellet would be frozen as it exits the glass and the wake behind would be clear instead of slightly blurred. Then imagine that having such a fantastic flash was within grasp of the amateur photographer. Now you can see why the thought of LEDs excites me so much.

Already many mobile phones have LED flashes built in. They work quite well, up to a few feet. Imagine that flash a lot more powerful and a lot faster. It would be able to freeze bullets in flight. Not just that - that's a side effect - but it would be lighter, safer and use less power. So why aren't they commonly available? Well, that's the thing - they need still some massive development.

Currently the amount of lighting power available from an LED is quite low. One would need a massive bank of LEDs to produce the light required for a flash. Now while it would be possible to build a light box with LEDs pointing inward and emitting their concentrated light though a small window rather akin to how many lasers function, I suspect there still isn't yet enough power from LEDs. I see tremendous potential for this technology in photography.

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