EDITORIAL

SECRETARY Brendan Keely FSLL bkeely@cibse.org

SLL COORDINATOR Juliet Rennie Tel: 020 8772 3685 jrennie@cibse.org

EDITOR Jill Entwistle jillentwistle@yahoo.com

COMMUNICATIONS COMMITTEE: Linda Salamoun MSLL (chair) Iain Carlile FSLL Jill Entwistle Chris Fordham MSLL Rebecca Hodge Eliot Horsman MSLL Stewart Langdown FSLL Bruce Weil Gethyn Williams

All contributions are the responsibility of the author, and do not necessarily reflect the views of the society. All contributions are personal, except where attributed to an organisation represented by the author.

COPY DATE FOR LL3 2020 IS 13 MARCH

PUBLISHED BY The Society of Light and Lighting 222 Balham High Road London SW12 9BS www.sll.org.uk ISSN 2632-2838

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FROM THE EDITOR

There is no doubt that photometrics are in a state of flux, luminous and otherwise. Challenging the orthodoxy of how we measure lighting is probably long overdue, but the introduction of LEDs, disruptive indeed, and the discovery of the non-visual photoreceptor in the mammalian eye are two developments that have perhaps accelerated the process.

It is always an alarming prospect to throw decades of thinking out the window, but tweaking rather than taking a fresh look at the whole thing can lead to compromise and complication. Committees and camels. Stephen Cannon-Brookes is one who thinks that a more radical rethink is in order (Tunnel Vision?, p9). The CIE definition of visible light using the photopic spectral sensitivity function known commonly as Vλ is under siege, he maintains. 'Our classical photopic-focused understanding of light [is] an increasingly creaking edifice,' says Cannon-Brookes. 'Addressing this, however, is a challenging prospect for the multiple generations brought up on an orthodoxy that also underpins our understanding of colour.' Mark Rea proposed the universal luminous efficiency function (Uλ) in 2016, and David Loe questioned the validity of Vλ in an article two years ago (Does Vλ SPD measure up? March/April 2018). Following up with another article based on further experiments (p11), he confirms his challenge of the established approach. 'The results suggested that the Vλ [SPD] as a basis of illumination metrology is at the very least questionable,' he says.

Perhaps the outcome will be a measure of boldness as much as anything.

JILL ENTWISTLE

JILLENTWISTLE @YAHOO.COM

CURRENT SLL LIGHTING GUIDES SLL Lighting Guide 0: Introduction to Light and Lighting (2017) SLL Lighting Guide 1: The Industrial Environment (2012) SLL Lighting Guide 2: Lighting for Healthcare Premises (2019) SLL Lighting Guide 4: Sports (2006) SLL Lighting Guide 5: Lighting for Education (2011) SLL Lighting Guide 6: The Exterior Environment (2016) SLL Lighting Guide 7: Office Lighting (2015) SLL Lighting Guide 8: Lighting for Museums and Galleries (2015) SLL Lighting Guide 9: Lighting for Communal Residential Buildings (2013) SLL Lighting Guide 10: Daylighting – a guide for designers (2014) SLL Lighting Guide 11: Surface Reflectance and Colour (2001) SLL Lighting Guide 12: Emergency Lighting Design Guide (2015) SLL Lighting Guide 13: Places of Worship (2014) SLL Lighting Guide 14: Control of Electric Lighting (2016) SLL Lighting Guide 15: Transport Buildings (2017) SLL Lighting Guide 16: Lighting for Stairs (2017) SLL Lighting Guide 17: Lighting for Retail Premises (2018) SLL Lighting Guide 18: Lighting for Licensed Premises (2018) SLL Lighting Guide 19: Lighting for Extreme Conditions (2019) Guide to Limiting Obtrusive Light (2012)

Code for Lighting (2012) Commissioning Code L (2018) SLL Lighting Handbook (2018)