Ecopia Blog

January 10, 2013

Are LED Lights Better?

Filed under: Alternative energy — Tags: , — JohnWM @ 9:11 am

 What are Watts?
Most of us understand how bright a regular lightbulb will be by it’s watts rating, we know a 100 watt incandescent (old type) lightbulb will be bright enough to use in the kitchen or shed and that a 25 watt CFL (Compact Fluoro) is as bright as a 100 watt incandescent because the CFL uses less electricity to produce the same brightness. Some of the newer technology incandescents like halogen lamps are more efficient, a 70 watt halogen will have the same brightness as the 100 watt incandescent, but still be less efficient than the CFL because all incandescents waste a lot of power is as heat.

Illuminating  with Lumens
Although watts are usually used to indicate a light’s brightness, in actual fact they are a measurement of the electrical power used. The proper term to describe the amount of illumination filling a space is the Lumen.

The 3 lightbulbs mentioned before all produce about 1300 lumens.  The incandescent is least efficient at 13 lumens per watt, next is the halogen at 18.5 Lm/watt and most efficient is the CFL at 52 Lm/watt. These three types of light can be directly compared because their light radiates outward in all directions.

LEDs are also categorised by their lumens output and their efficiency is calculated as lumens per watt of power consumed.

But knowing how many lumens an LED light produces is not enough information when selecting one because its light is not the same, it does not radiate outward as sphere of light with equal brightness in all directions, but just in one direction.

LED Lights Produce Light not Heat
LED lights are different because they produce light directly from electricity. Their light is made up of photons that are emitted from the flat top surface of the LED (light emitting diode). High brightness LEDs emit photons in such great quantities that a powerful beam of light shines directly outward from the surface.

The fact that light only shines directly outward from the diode’s surface is the main drawback because it only provides light directly in front of the LED. Therefore optical lenses are used to spread the light out. (The latest LED lights have beam spreads of up to 150°).

For instance, a 100 lumens LED with a beam spread of 80° will spread its light evenly in a cone-shaped beam of light spreading 40° to either side of the beam’s center point. An equally powerful 100 lumens light, but with a beam spread of 150° will have its light spreading out 75° on either side of the beam center. Both lights produce 100 lumens of light but the degree of beam spread will determine how bright each light will be.

Therefore we need to measure the light brilliance or intensity to show how they differ in brightness.

Bright lights have more Candlepower
Lumens (Lm) represent the total light emitted while Candlepower, Candelas (Cd), and millicandelas (mcd) correspond to the light intensity. Referring back to the two 100 lumen LED lights with the different beam spreads, we can measure their light intensities with a light meter to find the narrow 80° beam has an average intensity of 68 candelas (68000 mCd) while the broader 150° beam has an average intensity of only 21.5 Cd. This shows that while both lights have the same total light power in lumens, the narrow beam is concentrated into a smaller area of high brilliance while the broader beam is less brilliant but will illuminates a larger area.

LED light Colour
There is another variable called light colour that needs to be understood.
LEDs don’t produce natural white light so they use yellow phosphors, chemicals that glow, to produce white light from blue LED light. Different shades of white are produced, from cool white which is a bluish white to warm white which is yellowish white.

But are LED Lights really Better?
Their directional beam is more efficient because the light is not wasted by illuminating areas where it not needed, so LEDs are used in LED lamps and torches where they can produce very bright light with very low power consumption. The greatest need is for LED lighting is as a replacement for the old fashioned light bulbs, so multi-LED units are produced to simulate conventional 360 degree lighting. LED torches are usually rated using the mCd of the LEDs to indicate the brightness of the beam, while Lights for area illumination are rated in lumens for a given beam spread to indicate how much total lighting is produced.

LED lights are unrivaled in low power consumption but also they have a long service life,  in fact they never have to be replaced. They are also very tough,  handling rough conditions without breaking and can be used anywhere.

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