Aug 28, 2017: Recently, in a number of instances, citizens as well as municipalities of different cities across the globe have been demanding that only warm-CCT outdoor LED lighting should be installed. This has been supported by organizations like the International Dark Sky Association, which is in favor of CCT limits.
To such a scenario, American Medical Association (AMA) has added a new concern. Illuminating Engineering Society (IES) is also doing extensive research work on LED lighting color with the aim to make the drivers and pedestrians safe on the road safe during the night.
IES is also studying and analysing the AMA report, and will soon come up with a technical report as a response to AMA report. IES points out that since both IES and AMA are concerned about the interest of the general public, it would have been better if AMA had made an effort to team up with IES to make this report, Shirley Coyle, IES president, told a magazine.
The blame game
It appears that certain parties like to blame lighting color, even if the actual concern is related to poor lighting design or poor luminair design, said Coyle. A number of advanced CCT LED installations have occurred without any complaints. However, when complaints start coming in, it is usually regarding the color difference between the old sources like high-pressure sodium (HPS) against the LEDs.
Besides choosing a CCT that is suitable to the client and application, it is also vital to utilize well-designed luminaires that reduce glare. The other important task is to make sure that a lighting design is done to meet minimum IES standards, to limit light trespass and to meet the requirements of the client.
Is LED lighting color to be blamed or poor luminaire design?
In certain cases, the disagreement is driven and enlarged by those with their own desire to use warmer CCTs. Other people target outdoor lighting CCT based on circadian disruption, overlooking the other significant aspects of light intensity, duration under the source, and time of day, IES president pointed out.
Debatably, home lighting at night would cause more disturbance to the circadian cycle due to elevated intensities and longer duration rather than the short-term, low-level lighting experienced in most outdoor applications, making the spectrum of the outdoor lighting a comparatively minor concern, she highlighted.
Coyle said that individual preference of the client will differ with each application. It is usually seen that warmer 3000K CCT in a well-designed, visually-relaxing streetlight which is preferred for one neighborhood, while 4000K CCT is chosen for roads and highways.
When it comes to the safety issue, the most apparent flaw is that CCT is not the issue at all. CCT is an excessively simplistic value that illustrates the color appearance of a light source, and for these issues the vital metric to consider is the particular blue content and, particularly, the melanopic response, which cannot be captured in CCT. Hence, there is a disconnect between real lighting science and those leading the outcry based on CCT, Coyle pointed out.
IES TM-30 came into existence for a particular reason. And it was to deal with some deficiencies of CRI and to develop a substitute approach for the industry to test drive. A technical memorandum (TM) by IES is a document that serves the purpose of having a consensus-based document that offers new information for deliberation on the basis of good science and applications.
The content of the TM can ultimately find its way into recommended practice (RP) documents or the IES Handbook. IES have issued this TM-30 which is being examined by lighting practitioners in North America. On a global front, the methodology is being reviewed and considered by CIE working groups on color quality metrics.