What is an LED and how does it work?
A LED, or light emitting diode, is a semiconductor diode which has the ability to conduct an electrical current. The diodes are formed by combining two different semiconductor materials to form a P-N (positive and negative) junction. When current is applied, the negative moves to one side while the positive moves to the opposite. Light is generated when the positive and negative charges recombine.
LEDs are unlike other traditional light sources in that they do not simply fail. Instead, the LED’s light output slowly diminishes over time. For example, L70 is the point in hours that the lumen output has depreciated to 70% of the initial lumen output. L80 would be 80% of the initial lumen output.
The RGB white method and the phosphor white method are the two methods of producing white light with LEDs. The RGB white method produces white light by combining the output from red, green and blue LEDs. The phosphor white method produces white light in a single LED by combining a short-wavelength LED, such as blue or UV, and a yellow phosphor coating with one another.
Key terms related to LEDs
- Luminous Efficacy is the total luminous flux emitted by the light source divided by the lamp wattage and is expressed in lumens per watt (lm/w).
- Lighting Fixture Efficiency is the ratio of the total lumens exiting the fixture to the total lumens produced by the light source.
- Absolute Photometry is the evaluation of the performance of the combined LED fixture system. Prior to LEDs, luminaire performance was done using Relative Photometry which allowed fixtures and lamps to be evaluated separately.
- Fixture Efficiency is the ratio of the total lumens exiting the fixture to the total lumens produced by the light source.
- Delivered Lumens is the amount of a light source’s raw lumen output that reaches the intended illuminated area.
Now that you understand the LED technology and terminology a bit better, here are some considerations when evaluating your next lighting project:
- DON’T assume that all LEDs are created equal because they are not! Be sure to do your research.
- DO know who you are buying from. Use established manufacturers you can trust. Many early LED manufacturers are no longer in business.
- DON’T assume that any fixture can be converted into a LED. New and old technology don’t always mix.
- DO look for retrofit kits designed by the original manufacturer. Find out if retrofitting is the right choice.
- DON’T use lumen output alone to evaluate light sources. Look at fixture efficacy to determine efficiency.
- DO read the fine print and check the environmental temperature rating. While cold is rarely an issue for LEDs, heat can sometimes affect performance.
- DON’T forget that equivalencies are not always equal. Again, always do your research.
- DO pay attention to specific fixture listings and environmental concerns.
- DON’T assume that just because a fixture looks good on paper that it will work for you. Ask for samples if they are available.
- DO remember that technology is constantly evolving. Purchase extras if consistency is important to you.
- DON’T assume that all measurements and calculations are the same. Entrust one solitary source to do all the measurements to ensure consistency.
- DO remember to check your verticals. They are just as important as horizontals.
- DON’T assume that colors will look the same from all fixtures.
- DO pay attention to warranty information when choosing your LEDs.
- DON’T stop upgrading your lighting system after switching to LEDs. Take full advantage of your LEDs by pairing them with the appropriate control strategy.
- DO look into dimming, OCC and controls. They will increase the future value of your system.
- DON’T settle for fixtures that aren’t designed to be serviced. Look for fixtures with replaceable parts.
- DO include the additional maintenance savings of not having to change lamps and ballasts. Maintenance savings can be substantial.
This information was presented at our Product and Technology Expo. Click here to view the full presentation.
If you have questions about LED lighting or want to incorporate it into your facility, please contact your French Gerleman Account Manager or click here to request information