The Seven Great Myths of LEDs
26 May 2008
The Seven Great Myths of LEDs
Understanding the Real Advantages and Limitations of LED Light Sources
Myth #1
LEDs last forever While LEDs are long-lasting they can easily fade over time depending on ambient temperatures, how hard they are driven, and how effectively they are cooled. Lumen depreciation is predicted by looking at ranges of LED die temperatures and can vary depending on manufacturer, package and color. Because LEDs typically do not catastrophically fail, mean time between failure (MTBF) is not a useful metric when calculating lifetime.
Myth #2
LEDs generate no heat When LEDs are used for lighting they only radiate visible light and not infrared heat. However, LEDs do conduct waste that must be extracted from the LED system. These thermal issues are managed by carefully analyzing the projected heat load of a system and then developing a detailed thermal design for an appropriately sized heat sink. The larger the sink, the more efficiently and effectively heat is drawn from the LED and dissipated into the surrounding air.
MYTH #3
White Leds produce over 160 lumens per watt
Many LED chips manufacturers test their products on lab benches with short ``pulse`` tests that produce high output at room temperature conditions with results that are often misleading. However, over a long period of time, thermal issues result in a decrease in light output which significantly lowers the efficacy of the LEDs.
MYTH #4
3 Watt LEDs are brighter than 1 Watt LEDs
In LED lighting, there is no correspondence between wattage input and lumen output as there is with traditional lamps. Typically with LEDs, light is not directly proportional to power. For example, LEDs are rated for various power ranges. Therefore, three 3-Watt LEDs driven at 1 Watt each will likely have more output than one 3-Watt LED driven at 3 Watts.
MYTH # 5
LEDs are not bright enough Rooms, tunnels and even entire building facades are being lit entirely with LEDs today. By any measure, illuminance or luminance, LEDs have enough light output for use even in very large installations.
Myth #6
LEDs cost too much The ROI for the use of LED lighting systems in an installation is surprisingly rapid when taking maintenance and energy costs into consideration. In many cases, economic payback can be seen in less than two years. In addition, the cost of LED systems is continuing to drop rapidly.
Myth #7
LED light quality is poor The Color Rendering Index (CRI) for many white Light LED systems is in the mid 80s (out of 100), making it suitable for nearly all lighting applications, and continues to improve rapidly. Interestingly, research shows that people actually prefer light from LED sources and as a result, government, industry and academia are re-evaluating the CRI as a lighting metric. As LED lighting becomes an alternative for general illumination, manufacturers are focusing on developing high-quality warm white LEDs that are similar to incandescent sources.
