Another technology challenge for broad use of LEDs is their lack of compatibility with existing electrical systems.
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.
Compatibility with existing dimmers has provided another challenge LED lights. Existing wall dimmers have been designed for incandescent bulbs, not LEDs, so LED lights do not behave well with most wall dimmers unless properly designed. 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. Another issue with poorly designed LEDs is that they can flicker when dimmed with the most commonly used electronic dimmers.