LED Lights Comparison
LED lights compared to other types of lighting
Most of us understand how bright a light bulb will be by it's watts rating, we know a 100 watt incandescent (old type) light bulb will be bright enough to use in the kitchen or shed.
We also know that a 25 watt CFL (Compact Fluorescent Light) is as bright as a 100 watt incandescent because the CFL uses less electricity to produce the same brightness.
Some of the newer technology incandescent 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 incandescent lights waste a lot of power is as heat.
Measuring light quantity - 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, with the 3 light bulbs mentioned before all producing about 1300 lumens.
In terms of efficiency 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 they shine in all directions as a sphere radiating outward from the source.
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 a sphere of light in all directions, just in one direction.
How LEDs produce light
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.
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° (the widest beams currently available) will have its light spreading 75° on either side of the beam center.
So we can see that 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.
Measuring light intensity - Candela
Lumens (Lm) represent the total light emitted while 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.
LEDs are the most efficient producers of light.
Their directional beam is more efficient because the light is not wasted by illuminating areas where it not needed.
The greatest need for LED lighting is as a replacement for the old fashioned light bulbs but the directionality of the beam is restrictive so multi-LED units are produced to simulate conventional 360 degree lighting.
LEDs are used in LED lamps and torches where they can produce very bright light with very low power consumption.
LED torches are usually rated according the the spot brightness in millicandelas (mcd) 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.