Latest LEDs deliver high efficacy with low thermal resistance, making products less expensive

High power LEDs are being squeezed into smaller SMD packages to deliver more power, and thermosetting packaging material is being used to overcome heat dissipation challenges

By Kartiki Negi

Thursday, July 31, 2014: High power LEDs, SMDs and lamp LEDs are continuously evolving in terms of luminous efficacy and life span to meet general illumination and backlighting requirements. General applications for these LEDs include streetlights, bay lights, floodlights, etc. In the high power category, both multi-chip and single-chip LEDs are available and offer high efficacy like 160 lumens per watt and above. Let’s find out the latest trends in the market.

Latest trends and products

The new trend is for manufacturers to pack more power into smaller SMD packages. Increased use of a chip on board (COB) is the latest development, with which the industry is trying hard to bring more number of LEDs together so as to offer more lumens per watt. “This is a sign of maturity—that the market is ready to experiment beyond the limits that were earlier considered sacrosanct. Today, we have 1 watt in a 5050 PLCC package and 0.5 W in a 2835 PLCC package by incorporating a thermal pad that was earlier absent,” says Vijay Kumar Gupta, managing director, Kwality Photonics Pvt Ltd.

In addition to this, many companies are working towards improving the packaging technology of LEDs, particularly to address heat dissipation issues. The latest technology in the high power industry is based on thermosetting packaging material instead of standard plastic PPA packaging. As a result, heat dissipation is much better allowing high power 1 W operation, whereas standard plastic packages can only drive in the low to mid-power range of 0.06 W – 0.5 W.

Philips Lumileds has launched a range of LEDs in the last few months. In February 2014, the company launched the LUXEON Rebel ES Lime emitters that offer efficient, tunable white light. Lime enables highly efficient colour mixing by providing a convenient above blackbody colour point with optimal standalone efficiency of 200 lm/W at 350mA and 85° C. The spectral output of Lime is closely aligned with the wavelength that human eye cones are most sensitive to—555 nm.

In April 2014, Philips Lumileds came up with the new LUXEON CoB 1202 LED arrays, offering 130 lm/W at 85° C. This array, along with compatible reflectors and drivers, enables the most affordable downlights, spotlights and PAR38. “The LUXEON array LEDs deliver the highest efficacy available in the market with the lowest thermal resistance. CoBs also have the smallest light emitting surface (LES) with the best uniformity. This enables products with the highest efficacy in the least expensive systems,” says Amrith Prabhu, country manager, Philips Lumileds.

The performance range of the LUXEON CoB 1202 arrays is 130 lm/W hot, over a correlated colour temperature (CCT) range of 2700-5700K at a CRI (colour rendering index) of 70, 80 or >90. The typical output for warm white (3000K, 80 CRI) is 800 lumens when driven at 200 mA.

Nichia Chemical India Pvt Ltd recently launched the 219B-V1 high power series that delivers 170 lm/ W with a maximum driving capacity of 1500 mA with lower forward voltage. It has better thermal stability, better lumen maintenance and consistency at Ta85°C. “Its application areas are streetlights, bay lights and floodlights, to name a few. These are single chip LEDs and have an easy-to-handle secondary lens that is available with all big lens manufacturers. Hence, this gives us freedom to play with different types of light distributions,” says Chandra Bhanu, manager- technical, LED division, Nichia Chemical India Pvt Ltd.

Everlight’s existing range offers two different packages—XI3030 series and XI3535 series, using thermosetting packaging material. It comes with multiple variations, in standard 3 V and 6 V, with high performance and high voltage versions for more simple and cost effective driver designs, a super warm 2200 K CCT version to emulate halogen or incandescent lighting options, and individual colour versions for colour mixing or decorative usage.

“The new package is a good balance of high performance at an affordable cost. It is less than 20 per cent of the cost of traditional ceramic high power products. This package platform allows for different technological variations depending on the chips used, colours mixed and driver conditions,” says Ewing Liu, technical marketing manager, lighting application section, Everlight Electronics Corporation Ltd.

Launched in November 2013, Kwality Photonics’ KLSL505W105 Lm 350mA LEDs are a clever combination of optimal chip size and a high-volume lead frame. Earlier, this 5050 package was used only for 60-120mA ratings. Kwality also launched the KLSL2835W 65 Lm 150mA LEDs in the same month. Previously, the 2835 package was limited to 30-60 mA ratings only. “These LEDs allow manufacturers to retain old PCB footprints and yet graduate to higher power without increasing the number of LEDs. The 2835 W goes into bulbs and downlights, while the 505 W is used for low cost downlights and streetlights, without loss of performance,” says Vijay Kumar Gupta, managing director, Kwality Photonics.

In April 2014, the Taiwan Semiconductor Lighting Company (TSLC) launched high power IR LEDs, the C3535X-Inx1, for surveillance applications. TSLC is developing packaging based on hybrid technology for wavelengths that range from UV lights with invisible short wavelengths to visible light with long wavelengths of blue, green, red and IR. Developed with ceramic package technology, this LED is highly reliable, has high emission power and a long lifespan. “The C3535X-Inx1 has a radiometric power of 700 mW under currents of 1 A and a WPE of over 30 per cent. This can lower system costs even when incorporating all CCTV product features at the same time,” says Gopal Shukla, country manaer, SemiLED Taiwan Semiconductor Lighting Company.

Meanwhile, TSLC also launched new LED headlamp products, which are especially suitable for automotive and motorcycle headlight applications due to their excellent and high thermal stability, and high luminance characteristics. Considering the different design requirements of head lamps, TSLC offers a series of head lamp products including 2-chip, 3-chip, 4-chip and 5-chip versions. The total lumen flux can range from 400 lm to 1500 lm, and the maximum drive current can go up to 1000 mA. “The chip used in a head lamp has excellent high temperature stability and very low lumen decay even while operating in high temperatures, so it’s very suitable for high temperature applications such as headlamps in automobiles,” says Gopal Shukla.

The overall size of the emitter is only 20 mm×20 mm, so these products are able to operate with a second lens such as PES or reflector type and are used in high-beam, low-beam and fog lamps.

How to choose the right LEDs

When looking for suitable high power LEDs, it is very important for consumers to be satisfied with respect to several parameters (e.g., the lumen bin should be on the higher side while forward voltage should be on the lower side). One should always focus on the lumen maintenance and colour stability of the product after 10,000 hours of operation at higher temperatures. Factors such as the level of efficacy, quality of light, heat dissipation and renowned brands should be considered before zeroing in on a product.

Efficacy: Once customers have selected the lumens needed for their application, they must look for the best efficacy levels for LEDs, that is, lumens per watt (lm/W). This will reduce the operational expenditure of the LED fixture. High power LEDs have the flexibility to over drive or under drive to create different ranges of efficiency.

Quality of light: Reliability and quality of light in terms of colour consistency over time are some of the very critical points to consider when buying LEDs. The quality of the LEDs is measured in terms of how long it takes for the initial brightness and colour to deteriorate.

Heat dissipation: When selecting high power LEDs, buyers should ensure that they have enough heat sinking to dissipate the power needed to generate the required lumens from the LEDs.

Optics: Buyers should also consider what type of optics is being used, so as to ensure there are no hot spots and to create the correct light pattern.

Reputed brands: One should choose a renowned brand, which will not compromise on the quality of the LED die, phosphor, encapsulant and leadframe materials, which together determine the quality and performance of an LED.