Designs for Lighting (DfL) have been hosting a series of interactive workshops so far this year, designed to gauge feedback in the industry to preferred colour temperature in street lighting design. In addition, they wanted to discuss with the industry the pro’s and con’s of selecting different colour temperatures.

They launched the initiative at the Institution of Lighting Professionals (ILP) Summit in Glasgow in June as one of the Premier Corporate member workshops. Since then, they have gained more feedback at ILP regional events on 7th September in London, 5th October at ILP Lightscene in Northampton 26th October in Edinburgh and 2nd November at the HEA conference in Newport, South Wales.

“A robust debate spearheaded by the online poll.”

The format of these workshops has been perfect for facilitating the audience debate of the topic through discussions and an interactive online poll. The format of the workshop allowed the audience to give their thoughts on the issue.

During the workshop, the audience are asked a series of questions via their mobile phones or tablets and can view the results live on the screen.

We have collated the answers to see if there is a consensus from the different venues.

The first question asked simply “Which Colour Temperature would you prefer to light the road outside your house”. Interestingly, 57% of the 169 respondents would prefer a warm white source with a Correlated Colour Temperature (CCT) of 3000K or 2700K, whilst maybe surprisingly, 9% would prefer a Cool White 5700K.

The workshops include live demonstrations of colour temperature options available on the market from 2700K Warm White up to 5700K Cool White.

The audience were provided with information regarding the effect of CCT on luminaire performance and the variation of Spectral Power Distribution (SPD) with LED colour temperature options. In addition, some of the recent reports on LED and Health were discussed and some reports are suggesting that lower CCT’s should be specified, however there is still work ongoing to verify and provide more specific detail on this aspect.

The audience was then invited to vote for “Which colour temperature they would specify considering Spectral Power Distribution, performance and Visual Appearance.

The response to this question saw some participants moving from an earlier preference of Cool White (5700K) or Warm White (3000K) toward Neutral White (4000K). This resulted in a 50/50 split between those specifying warm white of 3000K or less and those specifying 4000K.

The third and final question asked the audience which criteria were the most important to them when specifying LED products.

The most popular considerations when specifying were “whole life cost” and “photometric performance” showing perhaps how the Industry has been forced to make huge revenue cost savings.

Our audience raised points relating to the appearance of objects and surfaces illuminated by luminaires of a neutral white colour temperature, noting that some buildings and surfaces can appear dull and de-saturated. We discussed the use of warmer colour temperatures in residential areas, or places where architecture would be better illuminated by luminaires of warmer colour temperatures.

It is important to consider the additional lighting levels required due to lower scotopic/photopic ratios in warm white luminaires compared to Neutral or Cool white luminaires. This inevitably leads to higher energy requirements which could be as high as 15% when compared to luminaires with a neutral white colour temperature.

Although saving energy is important and one of the key areas for local authorities to reduce their costs, it is equally important to consider the area to be illuminated in context and consider the colour temperature selection as one of the key characteristics in improving the ambience, on a par with the luminous intensity.

The various interactive workshops have seen 169 attendees participating; however, the live poll results and debate summary only reflect a small demographic of the industry.

Colour temperature selection is undoubtedly one of the hottest topics for debate, discussion and development within the industry.

We’re hoping to develop more in depth feedback on this important design issue, also involving the general public who may have differing views on LED street lighting’ says Ryan Carroll, part of the DfL team hosting the debate

Designs for Lighting will continue researching this area and intend to host the workshop at future events, to build up a wider representation of opinions within the industry and more importantly, the public.