Open up a typical low-cost LED bulb and you may find LEDs positioned willy nilly around a metal heat-sinking plate. It turns out that not a lot of thought goes into LED positioning on many bulbs aimed at consumers. Often the result is a bulb that consumes far less power than an equivalent incandescent device but which could consume even less power if there was a rhyme or reason to the LED placements.
A group of researchers in Taiwan think they may be able to help make LED bulbs more efficient. “Scientists can use the linear equation we derived for deciding the approximate positions of LEDs for other applications,” said Wei-Lun Liang of the National Taiwan University Micro Optics Device Laboratory. “This can substantially shorten the time required to determine LED positioning before fine-tuning the positions.”
Liang’s group designed an LED-based train headlight that uses a tenth of the energy required for headlights using conventional light sources. “Some LED headlight products sold on the market are designed with many LEDs that have outputs that overlap in large sections. These designs waste a lot of energy,” said Liang. “Our research showed that electricity use can be reduced by focusing on the best way to distribute the LED energy equally.”
In The Optical Society journal Applied Optics, Liang and other researchers led by Guo-Dung J. Su report the train headlight design uses ten precisely positioned high-efficiency LEDs able to produce a peak intensity of at least 200,000 cd and illuminate a person at least 800 ft. in front of the headlight. The design uses a bit more than 20 W.
The researchers overlapped the LED outputs just enough to create a large beam using two half-circular parabolic aluminized reflectors. The beams from each reflector combine to generate the light intensity necessary to meet U.S. federal guidelines. This circuits powering the LEDs sit in the horizontal divider separating the reflectors.
To figure out where the LEDs should sit in the reflectors, the researchers first estimated the best LED locations and then fine-tuned them using tests and simulations based on the resulting illumination patterns.
The linear equation the researchers derived came out of the optimization process for LED placement. The researchers also point out that headlights typically use a complete parabolic reflector surface. “We believe this is the first design to use a combination of two semi-parabolic reflector surfaces,” said Liang.