For the last hundred years, the incandescent light bulb has been part of our daily lives. We donít think much about it. Flip a switch and dark becomes light. Today this humble invention is facing obsolescence due to global government regulations mandating increased energy efficiency for lighting. In an incandescent lamp, less than 10 percent of the input power is actually converted to visible light. The rest is non-visible infrared and heat.
In the US, traditional 100W and 75W incandescent lamps are scarce and, this year, sales of 60W and 40W incandescent lamps will be phased out, as well. Technologies vying to replace incandescent include halogen, compact fluorescent (CFL), and LED. Of these, halogen and CFL have been in use for some time, while LED lighting has become practical only in the last five years because of dramatic efficacy improvements in the technology. Luminous efficacy is defined as the ratio of luminous flux (lumens or lm) to input power (Watts or W), or lm/W. Similar to fuel economy on an automobile, it is a measure of the efficiency of a light source. A comparison of common 60W equivalent light sources is shown in Table 1.
Table 1. Efficacy comparison of various light sources.
Figure 1. AC voltage and current into a lamp with and without TRIAC dimmer.
CFL and LED are the obvious choices for very efficient light sources with CFL seemingly the most economical at todayís market prices. CFLs have environmental concerns, though, as they contain trace amounts of mercury and require special disposal methods. Additionally, they generally donít dim well, or at all, with standard TRIAC-based dimmers. To be fair, early LED lamps were not perfect. Some products did not produce pleasing light, last as long as advertised, or dim particularly well either. This has largely been corrected as lamp manufacturers and electronics suppliers have addressed a number of these issues in response to meeting EnergyStar criteria.
So, why are LED lamps still so expensive? As with any new technology the initial costs tend to be high, but rapidly improve as commercialization increases. Incandescent lamps have been around for more than 100 years. Lighting class LEDs, less than 10. While incandescent and LED lamps may look similar on the outside, they are vastly different on the inside. Incandescent lamps produce light by applying electricity to a filament. The filament is a resistive load that glows white hot, making visible light. As P = I2R, raising or lowering the RMS current to the filament increases or decreases the brightness, making for a very simple light source whose brightness is easily controlled by simple phase-cut techniques such as those employed in TRIAC dimmers.
On the other hand, an LED lamp is a complex group of electronic and mechanical parts: LEDs, optical diffusers, heat sinks, and a switched-mode power supply (SMPS) to turn the 50 Hz to 60 Hz alternating current (AC) into constant direct current (DC) that is LED-friendly. It doesnít require much thought to imagine this is probably more expensive to make than an incandescent lamp -- a lot more.