The idea of an XL prize money on developing a light bulb may seem absurd but the amount of energy it would help save, which comes to 34 Terawatt-hours of power nationwide per year, does validate the huge offering. The entries were supposed to deliver at least 900 Lumens output, with a consumption of less than 10 watts, and a lifespan of at least 25,000 hours.

Energy saving is good, we hope they also keep the cost economics of the 21st century lighting substitute in mind.

The original report from October 2006 compared light power and energy using 1.3 to 3.2-megapixel camera phones. The new report includes data from 5-megapixel camera phones released in the last year, and also considers advancements in camera sensors, xenon flash units, high-power white LEDs (WLEDS) and LED flash drivers.

Tests again showed that the LED BriteFlash approach delivers more light energy than most xenon flashes in a thin form factor suitable for slim camera phones and digital cameras.

Clear pictures in dim environments require sufficient light energy — the total amount of light received by each pixel in the camera sensor — during image-capture time. “People often wrongly assume that light power, which is the brightness or intensity of the flash, is the key because it’s what draws our attention, but it’s really the light energy that counts,” said Pierre Mars, CAP-XX vice president of applications engineering.

To calculate light energy, one would multiply light power (in lux) by the duration of the flash exposure (in seconds): Light power (lux) x flash exposure time (sec) = light energy (lux.sec). Ten to fifteen lux.sec of light energy is ideal for high-resolution pictures:

–  Xenon flash tubes driven by electrolytic storage capacitors deliver
higher light power, but over a very short flash exposure.
–  High-current LEDs driven by a supercapacitor deliver lower light
power, but over a longer flash exposure to generate more light energy.

Flash solutions tested:

–  Xenon: SonyEricsson K800, LG KU990, Nokia N82 and Samsung G800, all
with 5-megapixel cameras but with varying size electrolytic storage
capacitors.
–  Standard battery-powered LEDs: Nokia N73 (3.2-megapixel) and N96 (5-
megapixel)
–  Supercapacitor-powered LEDs: To demonstrate the BriteFlash approach,
CAP-XX used a small, thin (20mm x 18mm x 3.8mm thick), dual-cell
supercapacitor to drive a two-LED array of Philips LUXEON® PWM4s at 2A
each or 4A total during the flash pulse.

Monochromatic light-emitting diodes cover a large part of the visible spectrum with high efficiency. For blue light, nitride diodes achieve external quantum efficiencies in excess of 65%. For red light, phosphor diodes achieve efficiencies of approximately 50%. However, so far no highly efficient monochromatic LEDs have been available for the “yellow gap” at around 560 nm.

Leveraging previous research on warm white light, the researchers succeeded in down-converting blue LED light into monochromatic amber light with a 595 nm wavelength and a color purity of 98.7%. The external quantum efficiency of the PC amber LED is at 30-40%, depending on temperature. Compared to direct amber LEDs, the new PC amber LED is two to five times as bright. It achieves a light output of 70 lumens at a 350 mA current.

There are numerous applications for the LUXEON Rebel PC Amber LED. It can be used in yellow traffic lights or signals as well as in cars’ turn signals or warning lights for construction sites. They could also be used in consumer electronics and their high efficiency makes them inexpensive.