Transitioning from Compact Fluorescent Lamps (CFLs) and incandescent lamps to LEDs (Light Emitting Diodes) raises questions of perceived product superiority. Is one better than another? Essential questions include: how much energy and money is saved as well as how much less lumens depreciate. Comparing these lighting forms is useless if you don’t evaluate the right elements. Regardless of what motivation exists behind the desire to switch to LEDs, research shows that LEDs consistently have low life-cycle energy consumption compared to CFLs and incandescent lamps.
Switching, retrofitting or installing a new LED system may cause increased up-front costs, but merged with reliable lighting and consistent and predictable light costs may produce a more productive lighting solution.
Transitioning to LEDs
What should be compared when making the transition? Lumen output/depreciation, LED lifespan, reliability and degradation over time are all important factors to consider.
Typically, lamps are rated by their wattage. Incandescent lamps and LEDs both come in various watts. But these watt numbers are not comparable. Watts tell you how much energy the lamp uses. Lumens on the other hand tell you how bright the light will be. The more lumens a lamp has, the brighter the light will be, and vice versa. According to energy.gov, a 100-watt incandescent bulb provides approximately 1600 lumens. The comparable LED bulb “averages only 17 watts and offers the same amount of light”. That being said, having less watts means less energy is used by the lamp. And less energy used by the lamp means that the LED uses a greater percentage of that energy to make light and produces a brighter light, versus less light and more heat as is typical in an incandescent. When less light is lost in application, more specific lighting design can be achieved.
Again lumens enter the discussion. LED lifespan must be looked at through lumen depreciation. How much loss of light is acceptable? The Illuminating Engineering Society (IES) recommends determining the life as the point at which the LED is 30 percent lumen depreciated. If the lamp is still emitting light, and the amount of light is acceptable for its application, then the lamp’s lifespan has not yet ended, even though the light is diminished. General consensus is that LEDs last about 10 times the number of hours of an incandescent lamp. That relates to about 1,000 hours for incandescent and 10,000 hours for LED.
All forms of lighting eventually fade in some manner. CFLs and incandescent lamps can simply shatter or illuminate less of an area over time. LEDs predominantly emit less and less light until their illumination is no longer valuable. That is why the comparison factors: lifetime versus reliability cannot be lumped together. Lifetime refers to specific parameters and specific conditions, under which the lamp will operate for such and such amount of time. Reliability, otherwise known as failure rate, refers to something specific or a lot of somethings going wrong and “end[ing] the life of a specific product or component.”1
But how much lumen depreciation is tolerable, before replacement is needed or desired? The typical slow-dimming of LEDs may extend the lamp life. But the typical definition of the lifetime of a lamp is when it no longer gives off light. Traditional lighting failure provides us with the equation that when half the lamps have failed, the lamp is considered to be at the end of its life. LED degradation happens over time – so, “when there’s no longer enough light”1 for the intended application, it has reached its end of life. But also important to note is “that insufficient or no light output is not the only reason a product may no longer be acceptable.”1 Intermittent LED failure or changing light color or light distribution anomalies could be considered other reasons for failure.
Reasons for failure
But lumens are not the only thing to consider in LED lifespan and reliability. Certain aspects of the lamps should be compared for usage costs and reasons for replacement: power management, thermal management, optical management, and luminaire assembly integrity.
Power management concerns the ability of the LED to properly control and filter current. An LED that fails in this may flicker.
Thermal management concerns the LED’s ability to conduct heat and either help lumen illumination or contribute to its depreciation.
Optical Management refers to an LED that “is correctly and efficiently shaped and directed toward the desired surface.”1 This impact is unlikely to cause failure; but it could create undesirable lighting conditions.
Finally, assembly integrity refers to the level to which LED housings are protected from “dust, moisture, vibration, and other adverse environmental effects.”1 Such elements are unlikely to render the lamp useless, but they still impact lighting applications.
It is clear that “commercial customers understand the trade-offs among energy efficiency, maintenance costs, and first cost of an LED product,”1 but considering lumen output, LED lifespan, reliability and degradation over time can yield important considerations about LED lighting product life and overall effectiveness.
1Quoted from Energy.gov