Electrical Compatibility
Another technology barrier for broad use of LEDs is their lack of compatibility with existing electrical systems. Because LEDs are such a critical part of lighting’s future, technologists are researching ways to address the problem.
Voltage Issues
LEDs are low-voltage devices that turn on between 3.5 and 4 Volts. The common voltages used in lighting applications are 12VAC, 24-28VDC, 120VAC and 240VAC (Europe, Asia). For the North American market, over 85 percent of lighting applications by volume are currently 120VAC common line voltage.
The LED, because it is a diode, must be driven with a constant current source. The incandescent bulb behaves mostly like a resistor over a wide range of voltages: Change the voltage or current and the light will dim in a linear fashion. This makes it easier to drive electronically than an LED. A resistor is inherently a voltage-driven device while a diode is clearly not. An LED light will require an electronic drive circuit while the incandescent bulb does not. This drive circuit is a cost element for LED lights, but not for incandescent lights.
Because the LED is a low-voltage device it is easier to design and build drive circuits for it that are for 12VAC and 24-28VDC. The 120VAC and 240VAC drive circuits tend to be more expensive due having to “drop” the voltage down to the LED’s 3.5-4.0 volt level.
Because such a large part of the lighting market is 120VAC, a great deal of research has gone into designs for line voltage applications. Many innovative designs have been developed and many more surely will be in the years to come. Using multiple LEDs in series or parallel/series have been used in many designs as a way to “stack” the LEDs so that the turn-on voltage of the LED string comes much closer to the 120VAC line voltage, thus making a lower cost drive circuit.
Dimmer Issues
Compatibility with existing dimmers is currently an issue with LED lights. Existing wall dimmers have been designed for incandescent bulbs, not LEDs, so LED lights do not behave well with most wall dimmers. Current LED lights may not begin dimming right away as the dimmer slider is moved, or they may be fully off when the slider is only 60 or 70 percent off. In a multiple LED light situation, turning down the dimmer may result in some LED lights turning off before others, or dimming non-uniformly. The issues around dimming LED lighting are well known and various efforts are underway to solve them.
There are many challenges ahead to make LED lights with better, lower-cost drive circuits for the line voltage markets in North America (120VAC) as well as Europe and Asia (240VAC). Compatibility with existing popular brand dimmers is important for the retrofit market. The replacement of wall dimmers is expensive and drives up the total cost of any retrofit project, jeopardizing the return on investment.