Whiter white and brighter coloured LEDs from Cree
Cree has announced white lighting LEDs for accurate colour reproduction, and has increased the output of its coloured LEDs.
White XP-G and XP-E devices will be available with a colour rendering index (CRI) of 80, 85 and 90.
“Many lighting applications, such as retail, medical and architectural, require high colour accuracy to properly render object colours,” said the firm.
CRI as high as 90 is seldom found in LEDs because hitting this figure generally reduces the lm/W figure too far to be marketable.
Ironically, to show what was possible with white LEDs in the early days, Lumileds offered a CRI of 90 from the warm white version of its 1W Luxeon Star and Emitter – industry’s first significant power LEDs.
They produced 20 lm/W, when their cool-white cousin was producing around 40 lm/W at a CRI of 70.
The efficacy difference is largely because high-CRI LEDs require more 450nm blue from the die to be converted to other colours, mostly red, to fill out the spectrum.
A CRI of 90 from single-die products has hardly been seen since the 1W Stars and Emitters.
“With previous generation high-CRI white LEDs, increasing colour quality meant decreasing efficacy,” said Cree.
And this is also true of Cree’s latest high-CRI offerings.
The firm has:
CRI=80 from 93.7 to 107 lm (minimum, at 350mA)
CRI=85 from 80.6 to 93.9
CRI=90 from 73.9 to 87.4.
These compare with 122 to 139 lm from its latest 5,000K cool white devices.
As 350mA typically represents 1.05W from Cree, lumens/Watt figures will be a fraction lower than the above figures.
To the firm’s credit, the CRI figures are minimum values, so all 80-CRI devices will be 80 or better.
For lighting, “using this XP-G, LED lamp designers can create systems that are 70% more efficient than a traditional halogen PAR38 lamp and deliver similar colour rendering”, said Cree.
At the same time, the firm announced improvements to the outputs of its colour emitting power LEDs.
At 350mA, XP-E devices are now available delivering minimum light output of:
500mW for royal blue
39.8 lm for blue
107 lm for green
73.9 lm for red-orange
62.0 lm for red
At the same current, XP-C LEDs are now available delivering minimum light output of:
350mW for royal blue
23.5 lm for blue
62 lm for red-orange
51.7 lm for red