An updated study has been published by Limited, developer of thin-form supercapacitors that compare flash solutions for camera phones -- xenon, standard LEDs powered by a battery, and high-current LEDs powered by a supercapacitor using the company's BriteFlash(TM) power architecture. The study tested each solution's ability to deliver the light energy needed to take digital-still-camera-quality pictures in low-light conditions, and also compared shutter requirements, ease of design-in, safety and size.
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.