Nokia sees increasing LED usage in mobile phones

June 28, 2006
LEDs are helping phone makers such as Nokia to add new functions to their phones, leading to increased shipment volumes and further innovation.
The number of LEDs used in mobile phones is likely to increase as more functionality is added, according to Barry Rowland, a technology specialist for Nokia in the field of LEDs and LED power management.

Speaking at PIRA-Intertech's conference "The Future of LEDs" earlier this week, Rowland said that camera flash using LEDs is going to be a "big market", and that added functionality using LEDs is on the increase.

"Handsets are likely to become more user-configurable," he said. "As one example, RGB LEDs can allow the user to change the keypad backlight color." Another example is the use of different colors to indicate the arrival SMS or email messages, or to differentiate between callers.

Earlier speakers including Asif Anwar of market research firm Strategy Analytics said that the overall market for LEDs in phones will be flat, mainly due to declining prices counteracting the growth in segments such as flash.

Rowland did not disagree with these views, saying, "As a major buyer, Nokia is pushing costs down." As far as Nokia is concerned, cost means not just the LED price but also includes the cost to use the LED with the required functionality, taking into account drivers, light-guiding, and many other factors. However, said Rowland, "lower prices mean that Nokia can use more LEDs for new functions."

Power consumption is always a key issue. Improvements in LED brightness, which have continued despite predictions that they would level off, translate to lower power consumption for a given display brightness. The introduction of LEDs with a lower forward voltage, down as far as 3 V, mean that these devices can be run from a battery without a boost converter.

More efficient LEDs -– Rowland estimated that lm/W values had increased by a factor of ten in 10 years -– in turn reduce the power drain and ease thermal management issues. "Since none of the functions are 100% efficient, we always have to consider how to get the heat out," said Rowland.

For keypad backlighting, a major trend is the introduction of very small and thin LEDs measuring 1 x 0.5 mm. "In a few years' time we will see 'paper-thin' LEDs with dimensions of 0.1 mm," said Rowland. "We'll be able to out them in places we never thought of." As well as leading to more placement and light-guide construction options, this will cancel out the main advantage of electroluminescence (EL) technology for keypads i.e. extreme thinness.

In the flash area, Rowland forecast a move from sub-2 W LEDs and drivers to the 4 W level. "I agree this is going to be a big market [for LEDs], " he said. "Customers have higher and higher expectations from their high-pixel-count cameras."

LEDs are giving large increases in delivered lux levels, and optics are becoming more sophisticated, so the drive levels may become limited by battery technology and could require the use of supercapacitors. Xenon flash is viewed as providing better light output and color rendering, but there are packaging issues, and LEDs can also operate in continuous mode for video filming.