FAQs
- What is an LED?
- Where have LEDs been used in the lighting industry?
- What is the history of using LEDs in general illumination lighting?
- How have lighting manufacturers perfected the technology to the point where LEDs are now very viable for use in general illumination lighting?
- Why don't LEDs function as efficiently in traditional fixture housing?
- What are the advantages to using LED lights?
- How do you evaluate LED products?
- Do I have to replace LED diodes?
- Why is the life span of an LED measured as lumen depreciation?
- How can LEDs outperform HID (High Intensity Discharge) lamp?
- If an LED fixture has lower initial lumen output than a traditional HID light, how can LED claim to deliver lumens more efficiently than HID?
- How does ambient temperature affect LED efficiency?
- What is junction temperature?
- How long is 100,000 hours?
What is an LED?
LED is the common abbreviation for a light-emitting diode. An LED is a semiconductor diode, which emits light when a voltage is applied to it. LEDs have been used in electronics since the early 1960's as indicator lights for various electronic devices. In more recent years, LED technology has progressed to the point where it is viable for general lighting applications. [top]
Where have LEDs been used in the lighting industry?
LEDs have commonly been used in aesthetic, effect, or specialty lighting applications, including architectural highlighting. Most traffic lights and exit signs, for example, now use red, green or blue LEDs. [top]
What is the history of using LEDs in general illumination lighting?
Early attempts to apply LEDs in general illumination lighting were not very successful because the first generation of LEDs didn't meet the lumen-per-watt output or color requirements. Also, conventional approaches to develop general illumination LEDs often involved retrofitting existing fixtures to house the new LED technology and traditional lighting standards were used to judge their performance. [top]
How have lighting manufacturers perfected the technology to the point where LEDs are now very viable for use in general illumination lighting?
LED manufacturers have been researching alternate materials and processes, dramatically improving the lumen output. In fact over the past forty years, improvements in this technology have exponentially increased the light output and efficiency of LEDs, doubling every 36 months. LED experts recognize that solid state lighting has many unique benefits and new thinking is needed in terms of the general illumination measurements for this new technology. [top]
Why don't LEDs function as efficiently in traditional fixture housing?
An LED module may physically fit into an existing housing, but that housing doesn't capitalize on the advantages of the LEDs. Standard housings can't handle the challenges of LED thermal management, which is vastly different than thermal management for traditional incandescent or fluorescent lighting. Also, the optical design used in most traditional fixtures doesn't maximize the LED's efficiency. [top]
What are the advantages to using LED lights?
LEDs bring several advantages to the lighting industry, including high efficiency and durability. With superior life over other lamp sources, their required maintenance is greatly reduced. This translates into energy savings, maintenance savings and an overall reduction in cost of ownership over the product's lifetime. [top]
How do you evaluate LED products?
Lumen output is part of the answer. To fully evaluate an LED product one needs to review the overall system efficiency, optical control and the thermal management. Products with good optical efficiency and thermal management will be able to deliver more lumens, on average, than traditional HID products. Another measure of LED performance is its life expectancy. [top]
Do I have to replace LED diodes?
An LED does not burn out like a standard lamp, so individual diodes do not need to be replaced. Instead, the diodes gradually produce lower output levels over a very long period of time. If one LED fails, it does not produce a complete fixture outage. [top]
Why is the life span of an LED measured as lumen depreciation?
The life span of an LED is vastly longer than that of incandescent, fluorescent or HID lamp sources, generally lasting 50,000 hours or longer. Although the LED never really burns out, product life span is measured by lumen depreciation and is typically stated to be when 70% of the original light output remains, shown as its L70 (L sub 70). [top]
How can LEDs outperform HID (High Intensity Discharge) lamp?
Super-bright white LEDs have the advantage of minimal lumen depreciation, better optical efficiency and high lumens per watt. This means these LEDs can be used to replace traditional HID luminaires. LEDs also have a vastly longer life span than traditional lamp sources. The fixture also must be designed to leverage the inherent advantages of LEDs. A comprehensive systems approach is needed for an LED product to bring all these features together. LED fixtures also have an environmental advantage in that they contain no mercury, last longer and produce less waste, and are made from fully recyclable materials. [top]
If an LED fixture has lower initial lumen output than a traditional HID light, how can LED claim to deliver lumens more efficiently than HID?
When you average delivered lumens over the course of 60,000 hours, an LED outperforms a 400-watt MH lamp operated in a horizontal position. (60,000 hours is used for this comparison to show three full life cycles of the HID.) The MH's lumen depreciation, as well as optical and ballast losses, quickly reduce output of the HID system. Conversely, LED has significantly better lumen maintenance and a more efficient driver. Also note that the LED fixture typically doesn't need relamping from zero to 60,000 hours. As illustrated below, the LED's average delivered lumens is 74% higher than HID over 60,000 hours. [top]
How does ambient temperature affect LED efficiency?
LED fixtures must be designed with junction temperature thermal management as a key component and use the correct LEDs. These products will then be robust enough to operate in most ambient temperature applications. Unlike fluorescent sources, cold temperatures do not impact the performance of LEDs. [top]
What is junction temperature?
Junction temperature is the temperature at the point where an individual diode connects to its base. Maintaining a low junction temperature increases output and slows LED lumen depreciation. Junction temperature is a key metric for evaluating an LED product's quality and ability to deliver long life.
The three things affecting junction temperature are: drive current, thermal path and ambient temperature. In general, the higher the drive current, the greater the heat generated. Heat must be moved away from the die in order to maintain expected light output, life, and color. The amount of heat that can be removed depends upon the ambient temperature and the design of the thermal path from the die to the surroundings. [Source: DOE] [top]
How long is 100,000 hours?
Based on how long a fixture is illuminated per day, here's what 100,000 hours works out to:
- 24 hours a day: 11.4 years
- 18 hours per day: 14.8 years
- 12 hours per day: 22.8 years
- 8 hours per day: 34.2 years
