Lumen Depreciation - Useful Life
The useful life of LED lighting products is defined differently than that of other light sources, such as incandescent or CFL. This is because LEDs typically do not “burn out” or fail. Instead, they experience lumen depreciation, where the amount of light produced decreases and light colour appearance can shift over time. Instead of basing the useful life of an LED product on the time it takes for 50% of a large group of lamps to burn out (as is the case with traditional sources), LED product “lifetime” is set based on a prediction of when the light output decreases 30 percent.
What are LEDs?
LED means “Light emitting diode”
How is LED lighting different than other light sources, such as incandescent and CFL?
LED lighting differs from incandescent and compact fluorescent lighting in several ways. When designed well, LED lighting can be more efficient, durable, versatile and longer lasting.
LED lighting products use light emitting diodes to produce light very efficiently. An electrical current passed through semiconductor material illuminates the tiny light sources we call LEDs. The heat produced is absorbed into a heat sink.
Common LED colours include amber, red, green, and blue. There is actually no such thing as a “white” LED. To get white light the kind we use for lighting our homes and offices, different colour LEDs are mixed or covered with a phosphor material that converts the colour of the light. The phosphor is the yellow material you can see on some LED products. Coloured LEDs are widely used as signal lights and indicator lights, like the power button on a computer.
LEDs and Heat
Because LED lighting systems don’t radiate heat the way an incandescent or halogen light bulb does, the heat produced from the power going into the product must be drawn away from the LEDs. This is usually done with a heat sink, which is a passive device that absorbs the heat produced and dissipates it into the surrounding environment. This keeps LEDs from overheating and burning out. Thermal management is probably the single most important factor in the successful performance of an LED product over its lifetime because the higher the temperature at which the LEDs are operated, the more quickly the light will degrade, and the shorter the useful life will be.
LED products use a variety of unique heat sink designs and configurations to manage heat, so they may look very different from each other. Regardless of the heat sink design, all LED products that have earned the ENERGY STAR have been tested to ensure that they properly manage the heat so that the light output is properly maintained through the end of its rated life.
DIFFERENCE BETWEEN TRADITIONAL AND LED LUMENS
Traditional lamps, (HID (Metal Halide, Mercury Vapour ETC) and fluorescent lamps) emit light in all directions, require reflectors inside the luminaires to “bounce” as much light as possible away from the lamp and fixture components to the target area. However, not all light can be effectively redirected. Typically, 40% or more of the light emitted from the lamp is trapped within the luminaire and does not reach the target area.
The result of this is that the stated lumen output of traditional globes may have a great variation compared to what the actual number of lumens coming out of the fitting is. Most companies will give a LOR (light output rating, this may have D or U in front of it for Downward or Upward light) for their fittings (expressed as a percentage), that will tell you what the minimum amount of lumen loss is, it is worth noting that this is done with new clean reflectors and the actual amount of lumen loss will get higher as the fittings age due to corrosion and dust reducing the efficiency of the reflectors.
Led lights deliver the majority their light in a reduced beam angle and usually do not require an external reflector for the light so they have a higher LOR.
The net result of this that the amount of lumens shown is usually what the fitting will deliver (fitting Lumens), please note there are some companies that promote “Chip LUMENS” this means the amount of lumens that the chips actually produce and does not take into account any losses due to clear covers etc. that may be put over the fitting to protect the LED chips. (Even clear glass will reduce light by 4% plus).