Aug 6, 2015

Application-Optimized LEDs for Lighting

Category: Illumination

Illumination-grade midpower LEDs should be designed for the specific application they are targeted to serve, instead of being retreaded from the display backlighting industry.

The world of general illumination continues to move to LED lighting, slowly but surely. LEDs therefore need to move to meet the needs of lighting applications that they serve, be it a retrofit A-style lamp or an outdoor lighting fixture. There is a perception that many of the LEDs we see on the market were force fitted into lighting applications, after they were originally conceived to serve the display backlighting industry, and there may be some truth underlying that view.

Take the ubiquitous 5630 LED package as an example — one would be hard pressed to describe it as a product designed to deliver 50,000 hours of lumen maintenance lifetime, or to endure contaminant off-gassing from a neighboring lighting component. The first 5630s were made from plastics and silicone that worked just fine under the benign conditions found in a TV (which, by the way, was getting replaced as soon as the next larger, cheaper model was available). But those same materials were clearly susceptible to various failure modes when employed in harsher conditions. The transition from a light bar behind the LCD panel to a light bulb used in a factory was not so easy after all.

Illumination-grade LEDs should be designed for the specific application which they serve, and each of these applications may have different design criteria. Two of the most basic parameters are flux package (in lumens) and efficacy (lm/W). An LED that emits 100 lumens at nominal drive current is unlikely to be used in an entry-level TLED (LED tube light), while a 180 lm/W LED will be overkill in a 40W A19 replacement lamp.



Applications addressed by mid- and low-lumen packaged LEDs

Applicaitons addressed by mid- and low-lumen packaged LEDs.



The chart illustrates the high-level applications for mid- and low-lumen package LEDs, defined as devices that emit anything from 10 to 100 lumens at nominal drive current. Their efficacy in this lumen range spans 110-180 lm/W at production volume, given current levels of technology. Surveying the portfolio of LEDs in the market today, we already see a level of application-based optimization taking place to serve these high-level buckets. Most of the major LED players have a 6V, 60-100 lumen part for the directional lamp, high/low bay market, just as they do a 3V, 40-60 lumen part that is finding its place in any of the A19 lamps.

The next level
The next level of optimization is based on a larger number of parameters and, if done right, will differentiate suppliers from one another and usher in greater adoption of LEDs in general illumination. The parameters include quality of light, reliability, and color/light control.

Quality of light may sound amorphous but is of great importance to lighting designers — it includes standard measures such as CCT/CRI and R9 values, as well as specific peaks in emission wavelength that accentuate colors of merchandise. An example of an LED tailored around quality of light is the LUXEON COB with a fine-tuned color spectrum that is targeted for retail settings.

Optimization around reliability involves selection of materials to prevent failure modes found in the specific application.

Color/light control can be achieved in the LED through package design, and is manifested in radiation pattern and beam angle or externally through the use of secondary optics. In the latter case, the LED itself will need to be optimized so that it can be easily coupled with the external device.

Going back to the 5630 example, you can see it is indeed possible to transform an LED that was developed for TV backlighting to one suitable for deployment as tunnel lighting. The plastic casing will need to be changed, along with the lead frame (and its plating), the silicone, and the phosphor materials. It will be a completely different LED from its predecessor, and rightly so, given where the midpower lighting industry is headed.

Originally posted on All LED Lighting