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Matthew O'Connor/MEDILL

Technology has come a long way since Edison developed the light bulb in the late 1800s.


After you hit the switch: How lights work

by Matthew O'Connor
Jan 19, 2011


Incandescent, fluorescent, compact florescent, light emitting diode. There are a lot of options today when it comes to lighting.

With Edison’s traditional bulb on its way out and newcomers CFL (compact fluorescent light) and LED (light emitting diode) taking its place, you might be wondering how light bulbs work, what makes one more energy efficient than the next, and why in the world some give off that horrid green hue.

Traditional incandescent bulbs haven’t changed much since Thomas Edison and Englishman Sir Joseph Swan pioneered the technology in the late 1800’s. Filaments have improved, gases have been added to the inside of the bulb, but the principle remains the same.

Two metal contacts form a base to support a pair of wires in the bulb that are connected by a thin filament. When an electric current is introduced into the system, it travels up one support wire, through the filament and down the other side.

This is where it gets a bit technical, but hold on to your hats and try to recall what you learned in high school science classes.

Free electrons of the electric current make their way through the filament slamming into atoms along the way. This process heats up the atoms in the filament and causes electrons inside to jump temporarily to higher orbitals. When the electrons come back down to their natural state, they give off a good deal of energy, which at high temperatures, is released as visible light.

“In an incandescent you’re heating a filament which releases a photon as an element of light,” said Nick Holonyak, inventor of the LED light and professor in the department of electrical and computer engineering at University of Illinois, Urbana-Champaign. “You’re mainly generating heat.”

That’s why incandescent light bulbs are so inefficient. Most of the electricity is used to heat the filament; light is produced as a side effect.

Without the old standby of incandescent bulbs, many consumers are turning to compact fluorescent bulbs.

“As far as pros and cons, CFL’s are quite efficient, and they’re fairly well established,” said Wendy Davis, a vision scientist in the Optical Technology Division at the National Institute of Standards and Technology in Gaithersburg, Md. “There are a lot that put up high quality light, are reliable and are inexpensive.”

Fluorescent lights use the same principle of creating light, but go about it in a different way.

Once again, electric current is passed through the light from one end to the other. Inside a fluorescent light are an argon gas and a small amount of mercury vapor. The electrons in the current interact with the mercury vapor which causes the release of ultraviolet light, based on the same principle outlined above.

That light is not visible to the human eye but when it hits a coating on the inside of the tube, called a phosphor, that coating reacts and creates the light you see. Different light colors can be achieved by using different combinations of phosphors inside the tube.

“That makeup determines the spectrum of the light,” Davis said. “You can boost the energy efficiency by making it more green, which people don’t really like.”

Then there is the LED, the only lamp that approaches pure efficiency, Holonyak said.

“It’s an electronic light source,” He said. “The current itself is part of the generation of the light.”

Light is generated in an LED by the movement of electrons through a semiconductor material. This material is usually aluminum-gallium-arsenide that has had impurities added to it to allow the movement of electrons.

A diode is made by bonding two types of the material together: one with extra negatively charged particles (electrons) and one with extra positively charged particles. Current is pushed through the diode causing free electrons to fall into lower energy level “holes” left by the extra positively charged particles. The electrons release energy as a light photon.

A lot of work is being done with LEDs to move the process toward 100 percent efficiency. A major issue is producing crystals that emit the perfect light color for consumer use.

But the father of LEDs said in the world of lights, there is no competition. “There isn’t any other lamp that gives it any challenge,” Holonyak said. “Incandescents are doomed. Fluorescents are doomed.”

The day when incandescent lights simply won’t be available is approaching, but people need not fear living in the dark.

“As we go forward it’s important for consumers to know that there are a lot of options,” said Peter Soares, marketing director for light manufacturer Phillips. “The options will be there. There will be really great choices.”

Incandescent, fluorescent, compact florescent, light emitting diode. There are a lot of options today when it comes to lighting.

With Edison’s traditional bulb on its way out and newcomers CFL (compact fluorescent light) and LED (light emitting diode) taking its place, you might be wondering how light bulbs work, what makes one more energy efficient than the next, and why in the world some give off that horrid green hue.

Traditional incandescent bulbs haven’t changed much since Thomas Edison and Englishman Sir Joseph Swan pioneered the technology in the late 1800’s. Filaments have improved, gases have been added to the inside of the bulb, but the principle remains the same.

Two metal contacts form a base to support a pair of wires in the bulb that are connected by a thin filament. When an electric current is introduced into the system, it travels up one support wire, through the filament and down the other side.

This is where it gets a bit technical, but hold on to your hats and try to recall what you learned in high school science classes.

Free electrons of the electric current make their way through the filament slamming into atoms along the way. This process heats up the atoms in the filament and causes electrons inside to jump temporarily to higher orbitals. When the electrons come back down to their natural state, they give off a good deal of energy, which at high temperatures, is released as visible light.

“In an incandescent you’re heating a filament which releases a photon as an element of light,” said Nick Holonyak, inventor of the LED light and professor in the department of electrical and computer engineering at University of Illinois, Urbana-Champaign. “You’re mainly generating heat.”

That’s why incandescent light bulbs are so inefficient. Most of the electricity is used to heat the filament; light is produced as a side effect.

Without the old standby of incandescent bulbs, many consumers are turning to compact fluorescent bulbs.

“As far as pros and cons, CFL’s are quite efficient, and they’re fairly well established,” said Wendy Davis, a vision scientist in the Optical Technology Division at the National Institute of Standards and Technology in Gaithersburg, Md. “There are a lot that put up high quality light, are reliable and are inexpensive.”

Fluorescent lights use the same principle of creating light, but go about it in a different way.

Once again, electric current is passed through the light from one end to the other. Inside a fluorescent light are an argon gas and a small amount of mercury vapor. The electrons in the current interact with the mercury vapor which causes the release of ultraviolet light, based on the same principle outlined above.

That light is not visible to the human eye but when it hits a coating on the inside of the tube, called a phosphor, that coating reacts and creates the light you see. Different light colors can be achieved by using different combinations of phosphors inside the tube.

“That makeup determines the spectrum of the light,” Davis said. “You can boost the energy efficiency by making it more green, which people don’t really like.”

Then there is the LED, the only lamp that approaches pure efficiency, Holonyak said.

“It’s an electronic light source,” He said. “The current itself is part of the generation of the light.”

Light is generated in an LED by the movement of electrons through a semiconductor material. This material is usually aluminum-gallium-arsenide that has had impurities added to it to allow the movement of electrons.

A diode is made by bonding two types of the material together: one with extra negatively charged particles (electrons) and one with extra positively charged particles. Current is pushed through the diode causing free electrons to fall into lower energy level “holes” left by the extra positively charged particles. The electrons release energy as a light photon.

A lot of work is being done with LEDs to move the process toward 100 percent efficiency. A major issue is producing crystals that emit the perfect light color for consumer use.

But the father of LEDs said in the world of lights, there is no competition. “There isn’t any other lamp that gives it any challenge,” Holonyak said. “Incandescents are doomed. Fluorescents are doomed.”

The day when incandescent lights simply won’t be available is approaching, but people need not fear living in the dark.

“As we go forward it’s important for consumers to know that there are a lot of options,” said Peter Soares, marketing director for light manufacturer Phillips. “The options will be there. There will be really great choices.”