What are LEDs?
LEDs, or light–emitting diodes, are semiconductor devices that produce visible light when an electrical current passed through them. LEDs are a
type of Solid State Lighting (SSL), as are organic light–emitting diodes (OLEDs) and light–emitting polymers (LEPs).
How is LED lighting different than other light sources, such as incandescent and CFL?
LED lighting differs from incandescent and compact fluorescent lighting in several ways. When designed well, LED lighting can be more efficient,
durable, versatile and longer lasting.
LED lighting products use light emitting diodes to produce light very efficiently. An electrical current passes through semiconductor material,
which illuminates the tiny light sources we call LEDs. The heat produced is absorbed into a heat sink.
Common LED colors include amber, red, green, and blue. There is actually no such thing as a “white” LED. To get white light, the kind we use
for lighting our homes and offices, different color LEDs are mixed or covered with a phosphor material that converts the color of the light. The
phosphor is the yellow material you can see on some LED products. Colored LEDs are widely used as signal lights and indicator lights, like the
power button on a computer.
LEDs are now being incorporated into bulbs and fixtures for general lighting applications. LEDs are small and provide unique design opportunities.
Some LED bulb solutions may look like familiar light bulbs and some may not, but can better match the performance of traditional light bulbs.
Some LED light fixtures may have LEDs built–in as a permanent light source.
LEDs are “directional” light sources, which means they emit light in a specific direction, unlike incandescent and compact fluorescent bulbs,
which emit light and heat in all directions. For this reason, LED lighting is able to use light and energy more efficiently in many applications.
However, it also means that sophisticated engineering is needed to produce an LED light bulb that shines light all around like an incandescent
LED bulbs that have earned the are subject to very specific requirements designed to replicate the experience you are used to with a standard
A-type bulb, so they can be used for a wide variety of applications. As the graphic on the right demonstrates, a general purpose LED bulb that
does not qualify for the ENERGY STAR may not distribute light in all directions and could prove to be a disappointment if used in a table lamp.
Incandescent bulbs produce light using electricity to heat a metal filament until it becomes “white” hot or is said to incandesce. As a result,
incandescent bulbs release 90% of their energy as heat.
In a CFL , an electric current flows between electrodes at each end of a tube containing gases. This reaction produces ultraviolet (UV) light
and heat. The UV light is transformed into visible light when it strikes a phosphor coating on the inside of the bulb.
The Basics of LED Lighting
an image of LED lighting after 100 hours
The useful life of LED lighting products is defined differently than that of other light sources, such as incandescent or CFL. This is because
LEDs typically do not “burn out” or fail. Instead, they experience lumen depreciation, where the amount of light produced decreases and light
color appearance can shift over time. Instead of basing the useful life of an LED product on the time it takes for 50% of a large group of lamps
to burn out (as is the case with traditional sources), LED product “lifetime” is set based on a prediction of when the light output decreases
LEDs and Heat
Because LED lighting systems don't radiate heat the way an incandescent or halogen light bulb does, the heat produced from the power going into
the product must be drawn away from the LEDs. This is usually done with a heat sink, which is a passive device that absorbs the heat produced
and dissipates it into the surrounding environment. This keeps LEDs from overheating and burning out. Thermal management is probably the single
most important factor in the successful performance of an LED product over its lifetime because the higher the temperature at which the LEDs are
operated, the more quickly the light will degrade, and the shorter the useful life will be.
photo of LED lighting after 1000 hours
After less than a year of use, a poorly designed LED product can flicker, shift in color, look dim, offer uneven light, or continue to use power
when turned off, among other problems.