interview epistar
RS SD
Will you take this approach a step further and introduce white-light sources based on red, blue and green LEDs?
No. [With our chipsets], the green colour comes from the blue phosphor conversion, rather than a green LED. Green efficiency [with our approach] is now around 90-100 lm/W. The efficiency of a red-green-blue LED would be lower than either a blue LED and just a phosphor, or a blue LED with a phosphor and a red LED. Using a green LED as part of three different chips packaged together also complicates assembly and control.
RS SD
You have developed high-voltage white light sources based on red and blue LEDs. How do these work?
The high-voltage LED is a product for the retrofit bulb market. Its voltage is closer to the mains – for example, 120 V, or 110 V. The aim is to bring the LED’s voltage to match the mains, and significantly reduce the driver cost and space, especially for the retrofit bulb application, because there is not enough space to put too much circuitry. The high-voltage LED can be a blue chip with phosphor, or blue and red chips plus a phosphor. But our best high-voltage LED combines blue and red chips, and can be introduced into the warm-white market.
RS SD
RS How do you achieve the high voltage?
The voltage for one blue chip is around 3.0 V to 3.3 V. So we put them in series – maybe 10 LEDs, so around 30 V. We are using semiconductor processes to bind them together. Semiconductor technology is well-suited to isolating very small devices and connecting them together.
What volumes of these high-voltage white light sources are you shipping today, and how do you project this to increase over the next few years?
SD RS
SD
RS SD
RS
Now it’s about 3 million per month, and we are focusing on increasing this to 10 million per month by the end of the year.
What are the typical performance figures for these white light sources?
So far we have three different sets to provide to our customers for these applications. They all have a CCT of 2700 to 3000 K, and a CRI greater than 85.
Our first is the standard set, around 100 lm/W. Our second is the premium set, around 120 lm/W, and the last is the deluxe set around 150 lm/W.
What level of efficacy is required to have success in the LED light bulb market?
For LED light bulbs, the main markets are for the 40 W, 60 W and 75 W. For the 40 W replacement, we are using the standard set, with 100 lm/W. The 60W replacement uses 120 lm/W, and if you need to go higher to 75 W, you need 150 lm/W. The bulb doesn’t have much space to put the light source and deal with thermal treatment, so efficiency is a big issue.
Epistar must have thought about becoming a vertically integrated manufacturer of LED lighting products, such as LED bulbs. Why has
Testing blue LEDs for long- term reliability
The high-voltage LED is a product for the retrofit bulb market. Its voltage is closer to the mains – for example, 120 V, or 110
V.The aim is to bring the LED’s voltage to match the mains, and significantly reduce the driver cost and space, especially for the retrofit bulb application, because there is not enough space to put too much circuitry
March 2012
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