Currently, the luminous efficacy of power LEDs is around 50lm/W (lumens/watt), which does not meet the requirements for home lighting. Therefore, many problems remain to be tackled to boost the power WLEDs (White LEDs) into home lighting, of which the luminous efficacy is the key factor. Although there are many factors which can influence the luminous efficacy of WLEDs, the following ones are worth paying attention to.

The U.S. Department of Energy recently released a study that estimates efficacy to be 100 lms/W by 2010. By one estimate, replacing the incandescent traffic signals in the United States alone with LED signals would save nearly 2.5 billion kWh annually. Red traffic lights, for example, pay back their initial investment in 2.5 to 3 years through energy savings. Savings due to reduced maintenance are significant, and can be a leader in cost savings when replacement is difficult or expensive.

1. The luminous efficacy of WLEDs is between 20~60 lm/W. This variance is subject to differences in chromaticity as well as wattage.

2. Phosphors with larger grain size may reduce the luminous intensity directly.

3. The anti-senility of phosphors can directly influence the life span of WLEDs. Besides, the anti-senility of epoxy resins can also influence the life span of WLEDs.

4. The reflection efficiency of reflective cup or LED lead frame is also a key factor which influences the luminous intensity.

Taking all the factors discussed above into account, we can see that the luminous efficacy of WLEDs may be enhanced by designing good light emitting channel, choosing proper phosphors and designing logical process. On the other hand, the junction temperature of LED has direct influence upon light output efficiency, device life time, reliability and emitting wavelength of LED. Thus, good design of heat dissipation can also significantly improve the luminous intensity of white LEDs and prolong the life span of them.