A bulb will work equally well on AC as it will on DC. The bulb is fragile however. The glass envelope can be broken and the filament can fail either by too high a voltage, or by thermal shock (Being taken from room temperature to white heat in milli- seconds will stress the metal. This limits the lifetime of the bulb).
LED stands for Light Emitting Diode. It is a product of the semi-conductor industry. A "normal" rectifying diode is made of silicon with some impurities; this allows it to pass some current in one direction only. An LED is made of more exotic semiconductor materials.
In use an LED exhibits a forward voltage drop. The voltage applied must therefore be greater than this before it starts to emit light, after which the amount of light depends upon the current passing through it. (The voltage across it remains more or less constant).
Therefore LEDs are considered to be current-controlled whereas bulbs are voltage-controlled. In most situations you use a resistor in series with the LED to control the current.
With LEDs only the brightness changes as the current increases, not the colour. Secondly the LED does not get hot – almost all the power is used to generate light. The light is emitted mostly in one direction, which is why it can sometimes be referred to as directional light; however there are ways to correct this.
An LED will shine if the current is passed through in the right direction. If the voltage is reversed it will not shine. And if the voltage exceeds the reverse voltage it can be irreversibly damaged.
An LED has a maximum forward current; exceed this value and it will shorten the life considerably. Not a good practice carried out by some to increase light levels.
This may seem limiting, but operated within safe limits, it will outlast conventional bulbs many times, possibly indefinitely.
Types of LEDs
They come in a variety of sizes and colours. The smaller sized axial lead LEDs (meaning that the wires come out of opposite ends). Followed by radial lead LEDs(the wires come out of the rear). You can also get bigger devices and wire-less "surface mounted types"
The colour depends upon the material it is made from. Common colours are red, orange, yellow, green, blue and white. White is a special case in that all LEDs are monochromatic (they essentially emit one colour of light). However, White LED’s contain a blue LED chip with a coating of fluorescent paint that absorbs the blue light and re-emits it at a lower wavelength, for the desired effect.
for information about the quality and standards of our LED Technology, see about us
Illuminance Terminology
As in any field of technology illuminance has its own language. To view the glossary/vocabulary of the key terms used, please view the Illuminance Terminology page.