Problems With White LEDs

Efficacy

• Efficacy is a measure of how well a light fixture converts electrical power to light. LEDs have now reached the 100-lumen-per-watt milestone -- which means they are economically competitive with fluorescent and incandescent lights over the lifetime of the fixture. Additionally, there's no fundamental reason that LEDs can't reach above 150 lumens per watt.

Brightness

• Although LEDs are efficient, they aren't necessarily very bright. That is, they put out a lot of light for a given amount of power, but they can't yet handle the total amount of power necessary to reach the brightness of a 100-watt bulb. It's widely believed in the industry that the problem will be solved when LED semiconductor chips are built on better base material, substrates that match the semiconductor crystal structure. Even then, the industry is still divided about whether to get lots of light by assembling many small chips or by building one really big LED chip.

Color Quality

• LEDs make "white" light differently than incandescent bulbs. In LEDs, a few colors are combined to make white. In one approach three (or more) separate single colors are mixed, and in another a blue LED lights up a reddish-yellow phosphor and mixes those colors together. This approach means that LEDs do not necessarily "render" color the way they would appear, for example, under sunlight. In addition, there are aging effects that change the color mix as LEDs age. These are issues the industry is facing, but they've not yet been fully addressed.

Thermal Management

• Because LEDs are so efficient, they waste less than half the electricity they use, as opposed to incandescents, which waste about 95 percent of their electrical energy. But the waste in incandescents (and in fluorescents) gets sent into the air through infrared radiation. In LEDs, the heat stays in the chip, unless care is taken to conduct the heat away from the LED. If the heat isn't conducted away, performance suffers -- and so does lifetime, which can drop dramatically beneath the 50,000 hours or so that LEDs "should" last. The industry understands this problem very well, but not every manufacturer is willing to spend the money to handle the thermal issues.

Integration with Existing Infrastructure

• Unlike incandescents and fluorescents, LEDs respond almost instantaneously when electrical current is turned on and off. But the existing infrastructure has been designed to control traditional lighting. Solid-state lighting using LEDs needs drivers integrated in the design to convert existing voltages into the voltages necessary to control the LEDs. Also, lighting designers, engineers and architects are familiar with traditional lighting and are not necessarily aware of the advantages and concerns associated with solid-state lighting.