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Warm White or Neutral White – A Neutral Comparison

Posted November 18, 2016

Designs for Lighting employee, Ryan Carroll was a participant in the ILP Western Region “Charles Endirect Mini Paper” session yesterday at Nailsea Rugby Club. Ryan delivered an excellent paper on “Warm White or Neutral White, A Neutral Comparison”.

When researching the talk, Ryan identified the really hot topics in the industry. The colour temperature of LED lighting is clearly the issue creating most debate amongst Lighting Professionals.

Ryan has been with Designs for Lighting for just over 18 months now, following his successful completion of the Lighting Design and Technology Honours degree at the University of South Wales. His degree gives him an excellent understanding in the physics of lighting. Coupled with support from the team at DfL and encouragement from Managing Director, Alistair Scott, it quickly became a great topic of conversation in the office.

Ryan explains:

“When we first started looking at this, it became clear there were a number of aspects related to colour temperature which were being discussed within the industry. Being faced with a time limit of 15 minutes for the mini paper, I decided to focus on the energy efficiency differences between neutral white and warm white LED sources, in relation to exterior lighting.

Local Authorities have been under increasing pressure to cut their budgets and expenditure since 2008. High costs associated with energy and maintenance of lighting assets needed to be dramatically reduced in order for public lighting to remain affordable. The implementation of LED luminaires provided a solution for local authorities.

LED sources typically come in CCTs between 2700K (warm white) and 5700K (cool white). Early implementation was focussed on the higher CCT values as they provide better lamp efficacy, however there are other issues related to the visual performance and comfort which need to be taken into account, competent lighting professionals have been guiding clients to reduce the CCT in recent years such that 4000K (neutral white) is now the most widely used option.

There are calls from some activists and clients to further reduce the CCT to 3000K (warm white) and I decided to investigate the implications of this in relation to energy consumption as 3000K (warm white) sources do not at first glance deliver the most favourable business case. Primarily, this is down to the physics behind the warm white LED chip, which requires more electrical power to provide the same level of light output (luminous flux) as the neutral white LED chip.

I decided to compare the energy consumption per kilometre of road between 3000K and 4000K to see if there was a business case for moving towards the warmer 3000K LED’s.

It can be seen in the example scenarios, that the difference in energy consumption between warm white and neutral white LED chips has reduced to approximately 10%-15% dependent upon the fluctuation of variables such as; roadway geometry, luminaire installation geometry, lighting class and optical distribution of the luminaire etc.

The difference tends to increase for subsidiary roads (as opposed to traffic routes) as the S/P ratio is a consideration from BS5489-1. As the S/P ratio of warm white luminaires is lower than that of neutral white luminaires, a subsidiary road that is illuminated with a warm white source will require to be lit to a slightly higher average and minimum illuminance.

Due to the increase in light levels and energy consumption, the business case for warm white sources is therefore reduced compared to neutral white (if based purely on energy consumption).

I am also aware that there are questions being raised around potential health implications for the use of cooler colour temperatures within exterior lighting applications and am keen to research this further. I hope to evolve the paper and present my findings at future events. It has been a great challenge so far and I’m interested to see the direction my research takes me!”

Designs for lighting were very impressed with Ryan’s research and presentation, Alistair commented;

It was great to see Ryan’s enthusiasm to take on a topic that is very relevant and sometimes controversial. Designs for Lighting understand the importance of this topic within the industry and will support Ryan in carrying out further research.”

DfL would welcome any questions you might have on this topic and areas you might like DfL to investigate further