Don’t put sales before science, lighting industry warned

THE LIGHTING industry has been cautioned not to put commercial sales ahead of the science when it comes to so-called human-centric or circadian lighting.

UL says a vertical illuminance at the eye of about 350 lx for warm sources and  about 200 lx for cool sources could provide a simple way of implementing circadian-effective light – but the SLL is cautious. Pic: Alex Ageev 2018

The Society of Light and Lighting, the UK learned body, says that ‘under no circumstances’ should commercial sales be prioritised, ‘when there is a lack of factual or proven evidence for the claims being made’.

In a position paper on circadian lighting, published today, the SLL states ’it is essential for the lighting industry to recognise the current limitations in our knowledge of the implications of introducing circadian lighting’.

It goes on to say: ‘whilst efforts to produce a metric for circadian lighting are a step in the right direction, with regard to providing a quality lit environment that does not have a detrimental effect on the health and well-being, it is premature in relation to our understanding of the elements that affect the human circadian system’.

‘It is these other intervening factors that we need to understand before we can provide a useful evaluation of the benefits of circadian lighting.

‘At present, we understand that individual lighting requirements will differ on the basis of age, chronotype and duration of exposure among other factors. A light history or context is required in order to provide a circadian lighting solution that will cater to individual requirements.’

‘Additionally, whilst research is ongoing, certain questions should be asked with regard to the validity of products and services claiming to offer the suggested benefits of circadian lighting’.

The SLL’s position paper appears to strike a more cautious note than some standards bodies, a number of whom have been prepared to include metrics for entraining the circadian rhythms of building occupants.

The US standards body UL this week unveiled its recommended practice and design guideline for those wanting to support circadian entrainment in buildings.  The design guide went out for public comment.  

The document is intended for use by those who design and specify lighting in buildings and wish to provide light for vision and for circadian entrainment for typical day-active people and night-inactive people.

The document provides a simple way of implementing circadian-effective light and a method for verification of effect on building occupants.

The recommended practice states: ‘The amount of light equivalent to that after one hour of exposure, capable of suppressing the production of melatonin at night by 30 per cent (a circadian stimulus, or CS, of 0.30) should be continuously available at the occupant’s eyes for a minimum of two hours during the daytime.   

‘In very simple terms, this  translates into a vertical illuminance at the eye (EV) of about 350 lx for warm sources and  about 200 lx for cool sources, but the exact amount depends upon the spectral power distribution of the light source’.

Last year, scientist Mark Rea of the Lighting Research Centre in New York recommended that occupants receive 254 lux of vertical illumination at the eye for at least two hours, ideally in the morning. It described the recommendation as a ‘stake in the ground’.


  • Learn about the latest in human centric lighting at the Workplace and Wellbeing Conference, taking place at the LuxLive 2019 exhibition at London ExCeL on Wednesday 13 November and Thursday 14 November 2019. Entry is free - see the full programme and register for free HERE.