More efficient high-CRI and string-dimming-binned leds from Cree

Cree LED has added higher efficiency high colour rendering index versions to its XHP35.2 leds, and introduced leds optimised to dim evenly when used in parallel

The company has used its latest phosphor fill technology between the led die for improved optical performance.

Optimised for indoor directional lighting, “Pro9 versions of the XHP35.2 HD and HI leds have up to 10% higher efficacy at 90 CRI vs Standard
95 CRI minimum options for XHP35.2, XHP50.3 and XHP70.3 HI LEDs”, it said.

Describing them as “drop-in upgrades in performance and light quality over the Standard versions”, the company is claiming ~10% power saving (see graph) compared with its Standard parts.

That said, they cannot be driven as hard – max current is limited to 700mA in the Pro9 parts compared with 1.5A for Standard.

This is still a lot of power in these 3.45 x 3.45mm leds, as they are four-die types with a nominal forward voltage of 12V (11.2V typ at 350mA and 85°C.

Max light output for the Pro9 parts is 849 lm for the lens-less HI (‘high-intensity’) versions and 983 lm for HD (‘high-density’).

THe apparent optical source size, seen by external optics, is 2.6 x 2.6mm for HI and 3.2 x 3.2mm for HD.

Cree’s recently introduced XP-G4 leds also came with Pro9 versions, as well as a white optimised for broadcast use. G4 leds have had a lot of work done to bring variation-over-angle back to the standards set by ‘pre-PCN’ XP-G2 leds.

Even dimming

At the same time, Cree introduced 2835 lighting leds – in its ‘J Series’ – that have been re-designed to dim evenly when wired in parallel strings – which it has dubbed ‘precision dimming’ leds.

“When operated in parallel strings, as is common in many linear led designs, ledDs driven at relatively low currents – less than 20mA for 3V mid-power leds – will exhibit unacceptable light output and hue variations across the strings, caused by normal production variations,” said the company.

These 3V 2.8 x 3.5 x 0.7mm leds will be available in 6,500 to 2,700K (ANSI) colour temperatures and some will have 80 or 90CRI minimum colour-rendering.

Find a technology backgrounder on Cree’s precision dimming leds here

and a document that puts the Pro9 XHP35.9 leds into perspective here