For many applications LED lamps are superior to incandescent lighting. So why is it that in tens of millions of switches, indicators, control panels, signs, annunciators, displays, decor lights and dozens of other applications, design engineers still specify incandescent technology? It might be that they're just a few years behind what's really happening in LED illumination.

Although advances made in LED technology in the past few years have dramatically broadened the applications for these rugged little light sources, it wasn't that long ago that red was the only "daylight-visible" colored LED. And that wasn't the only thing limiting their use!

Unlike incandescent bulbs that give off the full spectrum of light in a spherical pattern, LEDs emit a focused beam of a single wavelength (color) in only one direction, in a variety of angles. For many applications, such as indicators or switch illuminators, this is not a problem, but it took the development of multi-chip arrays (see Figure A) and high-flux LED chips (see Figure A.1) to begin to achieve the effect of an incandescent filament.

Major advancements in LED technology have taken place in recent years such as development of new "doping" technologies that increase LED light output by as much as 20 times over earlier generations, and allow the production of daylight-visible LEDs in virtually any color of the spectrum. In addition to red, yellow, and amber/orange, LEDs are now available in many colors from leaf green to ultra blue. Even white light, long  thought to be an impossibility, is now available in three different shades as a light-emitting diode. (see Figure B)

(see What White-Light LEDs Can Illuminate and How They Can Be Used in this publication.)

The efficiency of LEDs is most apparent in applications requiring color. Light from a typical incandescent bulb must be filtered so that only light from a particular part of the spectrum (e.g., red, amber or green, etc...) for example—is visible. While LEDs deliver 100 percent of their energy as colored light, incandescent bulbs waste 90 percent or more of their energy in light blocked by the colored lens or filter. Incandescent bulbs also waste 80 percent to 90 percent of their energy on heat generation to reach the temperature for which (Kelvin scale) they are designed. 
(see Figures C & R.1)

With LEDs you get a more color-controlled monochromatic intense light. Observe the color difference between the third brake light on many modern cars. One third of all third (center brake light) brake lights are red LED clusters. Many car manufacturers frequently use LEDs because the third brake light is often inaccessible and replacement is essentially impossible. The next time you're in traffic look for one of these and notice how much more vivid red this light is than that emerging from standard—filtered—incandescent taillights. (see Figure D)

The point is that what was once a fairly marginal light source isn't marginal any more. In many applications, LEDs exceed the energy available from incandescent bulbs and offer significant additional benefits making LED clusters and lamps as friendly to the environment as they are to the operating budget.

LEDs with standard lamp bases were once only competition for tiny miniature and subminiature bulbs called the T1 or 3 mm "grain-of-wheat" bulbs. Today LED lamps come in a wide variety of standard lamp bases, in sizes ranging from the grain-of-wheat T1 (3 mm) to medium-screw 25 mm G30 sized bulbs and larger. LED lamps are rugged durable, daylight visible and—a blessing to overworked maintenance personnel—have a life span far exceeding that available from current incandescent technology. (see Figure E)

Obviously, the material cost of the incandescent bulb itself is inconsequential—the real cost is in lost production, wasted labor and energy. What really costs is to have a machine down or perhaps an entire line—with skilled operators idle. That's not to mention the labor costs associated with the maintenance worker who could spend their time on more productive projects rather than changing light bulbs.

Depending on what it costs you to have a machine down and pay an operator and maintenance worker—even if it's just for a quarter of an hour—the real cost of relamping incandescent bulbs can be astronomical. (see Figure F)