LED Flashlights trends 2010
2010 marks the year that production white LED efficiencies surpassed the 100 lm/W threshold, while several LED manufacturers are reporting lab results in the 140 lm/W range. The adoption of LEDs into markets traditionally dominated by incandescent and fluorescent lights continues unabated. Even so LED market penetration in many of these markets is just beginning.
There is one market though where LEDs have already achieved near total market dominance and in a very short period of time. That market is portable lighting. In fact it is almost impossible to buy a flashlight that uses a conventional incandescent bulb. Xenon bulbs are still used in high lumen tactical flashlights, but recently released LEDs with very high lumen outputs will start to compete with Xenon in this space.
There are many reasons for dominance of LEDs in the portable light market. For portable lighting, battery life is paramount. It affects so many customer “care abouts”; size, weight, convenience and lifetime costs. Further LEDs are nearly indestructible and have extremely long lifetimes on the order of 30-40 thousand hours. The illumination pattern from most LEDs used in flashlights is more uniform than a traditional bulb. Finally there is an LED available for almost any portable lighting product and price point. White T-1 and T-13/4 lamps can be used in low cost flashlights and high brightness LED modules are available for high end tactical torches. Even high power infrared LEDs are now available as illuminators for night vision devices.
The design of an LED flashlight begins naturally with the choice of LED. Choosing the right LED affect all aspects of the design from driver selection, to optics and thermal management. Consumer level LED flashlights output around 100 lumens while tactical flashlight emit in the 200 lumen range. Avnet LED suppliers offer a wide variety of single LEDs that output 100 lumens or more and several suppliers have LEDs with greater than 200 lumens output. Off the shelf optics with a variety of beam angles are available for these LEDs, greatly reducing both design time and cost as well as production costs. Alternatively multiple lower power LEDs can be the right choice. Some LED manufacturers are moving toward small footprint LEDs that can be mounted very close together resulting in a high lumen output from a small area. Several of these products also have integrated lenses that focus the light into a narrow beam which can be advantageous for producing a focused beam allowing for a simpler optical design.
The choice of LED in turn dictates the driver selection. White HBLED in the 100-200 lumen range usually have a forward voltage around 3.4 V, although some of these devices actually have two or more LEDs mounted in series inside the LED package resulting in a higher forward voltage. Either way a boost driver is required except in the case of a single LED is powered by three battery cells in series. Several Avnet suppliers offer boost drivers optimized for portable applications, achieving high efficiencies (>85%) with a small footprint and with both a low component count and cost. A single boost driver, if designed with flexibility in mind, can be used across several products with different battery configurations and differing numbers of LEDs driven in series.
The last design concern is thermal management which is essential for both LED efficiency and reliability. Recent advances in LED technology have made thermal management significantly easier. For instance a single 100 lm/W a consumer level flashlight will consume on 1 W with about 1/3 of that power being emitted as light making the total required heat dissipation to be only 2/3 W. Additionally LED manufacturers have greatly reduced the thermal resistance of the LED packaging further simplifying the problem.