Scientific Seen

News, Commentary, and Tutorials from a Scientific Perspective

Luminaire is just a fancy word for light fixture. The amount of light put out by a traditional luminaire depends both on the fixture design and the light source within the fixture. Solid state lighting with light-emitting diodes is a different story. The lines between light source and luminaire are not distinct, so luminaire output is even more important than ever. That’s why specifications of the lumen distribution are part of the Energy Star requirements for solid state luminaires. Lumen distribution is reported on polar plots.

Read more: How to Read the Polar Curve of a Luminaire | eHow.com http://www.ehow.com/how_8544350_read-polar-curve-luminaire.html#ixzz22Qu44a8S

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Originally published at eHow, June 2011.

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Solid state lighting (SSL) uses computer-chip-like crystals to emit light. The mechanism by which they generate light makes them efficient and controllable.

Light emitting diodes (LEDs) are semiconductor devices made in roughly the same way as computer chips. Their light doesn’t come from a heated wire or excited atoms in a vapor, instead it is emitted from a solid crystalline chip, which is why it’s called solid-state lighting. There are a few different processes that can be used to build semiconductors, but they all start by building a crystal.

A crystal is defined as an arrangement of atoms with long range order. Imagine a billiard table packed full of billiard balls, with no room in between. Then put on another layer of billiard balls, then another, each resting in the “pockets” where the balls on the previous level come together. If you know where the center of one billiard ball is, and the direction of the sides of the table, you know exactly how far to go to find the center of another billiard ball, in all three directions. That’s what solid state physicists mean by “long range order.” The long range order creates effects with far-reaching consequences.

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Originally published at Suite101, 29 MAR 2011

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Compact fluorescents (CFLs)-energy-saving, weird-looking, or ugly. No matter what you think of them, their physics gives them efficiency.

In fluorescent lights, electrical current doesn’t run through a metal, but goes through gas confined in a tube. Ordinarily gas can’t carry an electrical current because all the electrons are tied to their atoms. So the first thing a fluorescent lamp does is inject some electrons into the tube, then speed them up with high voltage. That flow of electrons surges through the tube, hitting against other atoms.

Just as in a solid, some of the energy of the electronic current goes into heat, but the voltage puts the electrons into a narrow energy range, and because the gas is thin—not dense like a metal filament—the electrons stay in that narrow range as they fly along. The narrow range can be tuned to transfer just the right amount of energy to a specific atom, so very little is wasted.

In fluorescent bulbs the specific atom is mercury, and the “right amount” of energy puts a mercury atom into an excited state. That mercury electron returns to its lower energy state by emitting a photon. (That’s why it’s not so easy to dim a fluorescent bulb: turning down the voltage changes the speed of the electrons rushing through the gas, which messes up the way they’re “tuned” to the mercury atoms, which pretty much shuts the bulb down.) While in incandescent bulbs most of the photons are in the invisible infrared wavelengths, mercury atoms emit their photons in the invisible ultraviolet region of the spectrum. To turn those invisible photons into visible light the inside of a fluorescent tube is coated with phosphor.

http://suite101.com/article/zapping-atomshow-fluorescent-lamps-work-a362596#ixzz228MqFhfo
Originally published at Suite101, 29 MAR 2011

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Incandescent bulbs have become-literally-a fixture of modern life. We’re used to them, but they’re a long way from an ideal light source.
A lit incandescent bulb has one predominant feature. Sure, it’s light in terms of its weight. And it’s fragile. It’s even bright. But, more than anything else, it’s hot.

Heat is a measure of how energetically atoms are moving within an object. Even in solids, atoms move around, bumping against each other. If the atoms within an object are relatively stationary, the object is cool, while a hot object is full of atoms sliding back and forth. In a burner on an electric range, for example, electrons push through the coil, crashing into other atoms along the way. These collisions put the electrons in excited states, and they release that energy as they transition back to a lower energy state.

A River of Electrons
The electrical current is kind of like a river, with some electrons flowing quickly and smoothly, while others bump and crash their way along. Then electrons that have been crashing along find some open space and rush by, while some of the quickly flowing electrons crash and slow down. So at any instant some electrons are moving very quickly, while others are moving slowly—but most are toodling along somewhere in between.

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Originally published at Suite 101, 29 MAR 2011

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Today’s consumer can choose from incandescent, fluorescent, and solid-state lighting. The science behind each drives their performance.

Currently, consumers have three options: incandescents, fluorescent bulbs, and the new kid on the block, solid-state lighting from light emitting diodes (LEDs). But incandescent bulbs are on their way out. The European Union and the United States have both enacted regulations on lighting energy usage that will eventually ban most traditional incandescent bulbs. Governments have nothing against old-fashioned light bulbs — except that a large percentage of the energy utilized by the bulbs use does not create light! The inefficiency of incandescent bulbs has very little to do with how well they’re made; it’s due to the fundamental physics involving light.

At the heart of each lighting method is the same basic process: an electron gets rid of energy, emitting a tiny amount of light. The color of the light depends upon the amount of energy the electron gives off; blue light has higher energy than red. Different light sources are distinguished by the different ways they put energy into electrons and the different way the energy comes out of the electrons.

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Originally published at Suite101, 29 MAR 2011

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