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Talking Photometry: Claimed vs Actual CCT

Testing conducted for the United States Department of Energy (DOE) CALiPER programme reveals that many LED retrofit lamp products fail to meet their claimed colour quality specifications. In a special report from 2011 on 30 SSL replacement lamps - including MR16/PAR16, PAR20 and PAR30 - the DOE found that over one third of the lamps tested had correlated colour tempertures (CCTs) far higher than their rated (specified) values. Click here to download the CALiPER report.

CCT   It is well known that LED colour temperature varies with temperature (see: "Are LED Specifications Made Up?"). LEDs are tested and binned at a junction temperature of 25 deg. C, whereas in a typical lamp or luminaire, the operating temperature can be in excess of 60 deg. C. As (physical) temperature goes up, so too does the correlated colour temperture of the LED. Not only that, any optics or reflectors used with the LEDs will further shift the CCT. All of which means that there is a real danger in assuming that the colour of the component LED will apply to that of the lamp or luminaire into which the LED is fitted.

The CALiPER report reveals that most of the LED replacement lamps were specified by the manufacturers with rated CCTs in the range from 2700-3000 Kelvin, in other words "warm white" and comparable to tungsten bulbs. However, upon inspection, over one third of the bulbs were found to have CCTs of over 4000 Kelvin and one - labelled 4000K - was actually giving out light at over 8800K!

This report serves as a clear warning that it is vital to test the finished product if you are to avoid consumer dissatisfaction. Photometric Testing provides a full service to those developing solid state lighting - not only can we accurately measure CCT, we can also verify bin selection, and measure luminous flux and CRI values using our state-of-the-art spectroradiometric equipment.

 

Click here to download the CALiPER report.
Click here to go to the DOE Solid State Lighting web portal.