LED (Light Emitting Diode)

Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world. Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary incandescent bulbs, they don't have a filament that will burn out, and they don't get especially hot. They are illuminated solely by the movement of electrons in a semiconductor material.


LEDs offer the potential for cutting general lighting energy use nearly in half by 2030, saving energy dollars and carbon emissions in the process. Their unique characteristics listed below are beneficial in many lighting applications including traffic lights, night lights, store signs, holiday lights, exit signs, flashlights, desk lamps and cooler display (saves cooling costs due to reduced heat output!):

  • High energy efficiency (70 - 120 lumens/watts and improving rapidly, DOE's long-term R&D goal calls for cost-effective, warm-white LED packages producing 250 lumens per watt by 2025);
  • very long life and ease of maintenance;
  • compact size;
  • resistance to breakage and vibration;
  • good performance in cold temperatures;
  • instant-on performance (i.e. reach full brightness instantaneously, while CFLs could take a few seconds to 60 seconds under cold temperatures);
  • ability to be fully dimmed (double-check on the packages to make sure the LED models are dimmable);
  • Good light quality (most LEDs' CRI are in low 80s, some can be as high as 92);
  • Unaffected by frequent on/off cycle (unlike CFLs);
  • Contain no mercury (unlike CFLs)

http://my.ilstu.edu/~gjin/p2/Lighting_P2_in_Energy/EXLT6-4E12-001_exit-web.jpg LED-flashlight.jpg   http://my.ilstu.edu/~gjin/p2/Lighting_P2_in_Energy/LED%20lamp.jpghttp://my.ilstu.edu/~gjin/p2/Lighting_P2_in_Energy/FRESH%20LED%20DESK%20LAMP%20BY%20VICTOR%20VETTERLEIN1.jpgLED-cooler-display.jpg  

The following video by Lithonia Lighting covers the basics of LED lighting technology and also reviews some basic terminology of lighting we have discussed earlier such as lumens, lighting efficacy, color temperature, etc.

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To learn more on how LED works, click on this.

LEDs offer a huge variety of benefits but at the same time they cannot be viewed as the optimum solution for every lighting-related application. Some challenges faced by these devices include:

High Price: LEDs are currently more expensive, on an initial capital cost basis, than most conventional lighting technologies. However, when considering the total cost of ownership (including energy and maintenance costs), LEDs far surpass incandescent or halogen sources and begin to threaten compact fluorescent lamps.  

Temperature Dependence: LED performance largely depends on the ambient temperature of the operating environment. Over-driving the LED in high ambient temperatures may result in overheating of the LED package, eventually leading to device failure. This is especially important when considering automotive, medical and military applications, where the device must operate over a large range of temperatures, and is required to have low failure rate.

Light Pollution: Light pollution occurs when too much artificial illumination enters the night sky and reflects off airborne water droplets and dust particles causing ' skyglow ', and consequently drastically limits the visibility of stars. The strong blue light emitted from cool-white LEDs scatters much more efficiently through Earth's atmosphere, compared to other colors . This means that cool-white LEDs can cause more light pollution than other light sources. It is therefore very important that cool-white LEDs are fully shielded when used outdoors.   Compared to low-pressure sodium lamps, the blue light emission spike of cool-white and blue LEDs is scattered about 2.7 times more by the Earth's atmosphere. Cool-white LEDs should not be used for outdoor lighting near astronomical observatories. Evidence also shows that excessive artificial lighting disrupts the behavior patterns of nocturnal animals.

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Summary of Energy Efficiency of Various Types of lamps

The following charts provide us with a summary of energy efficiency measured by lumens/watt of different types of lamps. Depending on the source of the information, lumens/watt reported for each type of lamps vary.



It is also very important to note that simply picking the most efficient lighting in terms of highest lumens per watt is not always the best choice. One has to always keep in mind the light quality and the applications, the video below provides a good example of factors to consider when making energy efficient lighting decisions!

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