Application Watch: Initial foray into water-resistant high power LEDs under way

A few China LED suppliers have begun offering more advanced watertight high-power LEDs for the outdoor advertising display market.

Sustained high growth of the global LED display industry is keeping the LED sector dynamic, spurring manufacturers of the component to take product development a step further. In China, midsize and large LED suppliers have raised the ante by releasing water-resistant high-power types, zeroing in on the lucrative outdoor advertising market. Foshan NationStar is among the few that have done so, offering watertight SMD units for different outdoor uses. Like similar products on the international market, such variants while more expensive can be used without a protective shield and contribute to lower total display cost.

For most local makers, however, the thrust remains on standard SMD LEDs whether for indoor or outdoor displays. Companies said the sealed construction of the latter application already provides protection for the diodes. They focus instead on achieving consistent brightness and wavelength. Efforts also cover extending product life span by adopting quality epitaxial and package materials, mainly from Cree, Epistar and San'an, to reduce thermal resistance. So far, the longest realized operation is 500,000 hours.

China manufacturers also sustain the development of smaller SMD diodes. Foshan NationStar has introduced 3.5x3.5mm, 2.7x2.7mm, 2x2mm and 0.8x0.8mm models for P4 and below outdoor LED displays, all of which are water-resistant. Its 0.6x0.6mm units, likewise in watertight construction, are under trial production and scheduled for market release in one or two years. The company also has a water-resistant SMD LED that integrates three RGB chips, especially designed for outdoor LED displays.

At present, SMD and DIP diodes have almost the same shares of China's output for LEDs for this application. But this will change as the former is expected to accelerate in production, driven by the trends for high definition and finer pitch in advertising displays.

The worldwide LED display market is projected to maintain 15 percent growth in the next few years, according to Sohu. From this, the majority of China makers anticipate demand to climb by 10 to 15 percent in coming months. They are upbeat about this, especially because the country is the largest manufacturing base for LED displays. China is responsible for more than 50 percent of global shipments, with reach spanning North and South America, Europe, the Middle East and Southeast Asia.

Over half of the LED makers in China are in Guangdong province, specifically in the cities of Shenzhen and Dongguan. All companies, including foreign businesses, turn out LED modules and strips as well. Diodes for advertising displays represent 10 to 15 percent of their aggregate deliveries.

SMD & DIP high-power LEDs

For advertising displays, typical high-power LEDs from mainland China suppliers come in 0.5 to 1W for SMD types and up to 0.5W for DIP variants.

SMD diodes are mainly in sizes of 3535 and 2727. The former finds wide adoption in P8 and P10 displays, while those in 2727 are used mostly in P5, P6, P6.25 and P6.67 displays.

Ningbo Sunpu Opto Semiconductor Co. Ltd's model SL-522WCDC-06G white LED with a 5mm lens has 800 to 20,000mcd brightness and 100,000-hour life span. The rated voltage is 1.8 to 3.8V and the rated current 20mA. The maker uses silicone casting for this unit designed mainly for LED displays.

In general, suppliers can develop products based on buyers' specific requirements.

All releases are RoHS-compliant. Those from Shenzhen Fedy Technology Co. Ltd have additional CE and FCC certification. Forty-one percent of the maker's 50 million unit-output consists of high-power LEDs and the remainder diode components.

Manufacturers use LED chips from Taiwan or US providers, primarily Cree, Epistar and Chimei. For lower cost, some turn to local companies such as Lattice and San'an. Exceed Electronic Co. Ltd adopts about 90 percent of inputs from Taiwan and Japan.

Other materials and components come mostly from domestic sources, while imported kinds are employed on request only.

The cost of local inputs decreased in the past year, resulting in a 5 percent reduction in LED prices. In the months ahead, outlay and quotes are forecast to stay steady.