THROUGH THE AGES

Iain Carlile finds past and present concerns in the most recent online papers from Lighting Research and Technology

Iain et al have examined how the circadian effect can change due to age-related changes in the eye. The study measured corneal illuminance and the human eye’s spectral transmittance, with age-related change, at different spectral power distribution (SPD) values. These values were created using red-green-blue-warm-white (RGBWW) colour-mixing LEDs to create five different SPDs with CCT/CRI values of 2700K/95 Ra, 4000K/96.6 Ra, 5000K/96.8 Ra, 6500K/95.6 Ra and 8000K/93.5 Ra.

The results showed that, as a general trend, the effect of the circadian stimulus (CS) increased with CCT from 4000K to 8000K at the same age, but at 2700K CCT a higher circadian impact was noted compared to that of 4000K for the same age groups. It was also noted that at consistent CCT the CS value increased with corneal illumination but decreased with age. Also, at the same corneal illuminance the CS value of different age groups may be the same at different CCT values.

The authors suggest that their results could be used to create personalised video display terminals and that interior lighting could be tailored from the perspective of circadian effect. However, they note that there are many other factors related to age that might also have an impact.

Vries et al present a study on lighting in the office environment. They investigate changes in desk, and therefore task illuminance, while maintaining a constant wall luminance, and the impact this has on a user’s performance, mental state and perception of the surrounding space.

A simulated office space was created with five workstations in an open-plan style layout,

p A diorama of William Murdoch

demonstrating gas lighting at his home in Redruth, Cornwall, c1794 (from The standardisation of light and photometry – A historical review)

and daylight was excluded by using opaque blinds. The space was lit with ceiling-recessed 600 x 600mm office-style luminaires, with adjustable spotlights providing wall illumination. All luminaires were dimmable, with ceiling fittings used to adjust the desk illuminance, and spotlight wallwashers raised/dimmed to ensure a constant wall luminance between the different experimental conditions. Three different desk illumination conditions were used: 150 lux, 500 lux and 1500 lux, at a uniformity of 0.8.

It was found that visual acuity of paperbased tasks and perceived brightness increased significantly with higher desk illuminance, however the room’s attractiveness did not. Illuminance at the eye rose significantly with increased desk illuminance but had only minor effects on subjective alertness and cognitive performance.

The authors conclude that while task illuminance for visual acuity is an appropriate design parameter, it has little to no impact on the attractiveness of a space, nor the cognitive or mental state of office occupants. They recommend that a more comprehensive approach to office lighting design is needed.

Bertenshaw’s paper provides a historical review of the standardisation of light and photometry. He looks at the technological challenges and solutions that were faced in creating reproducible standards and measurement of light from the 18th to 21st century, exploring some of the social, political and economic reasons for doings so.

He looks at the evolution of lighting from candles, through to gas lighting and incandescence, setting out the different historical standards for each, and on to the current radiometric definitions.

Iain Carlile FSLL is a past president of the SLL and a senior associate at dpa lighting consultants

Lighting Research and Technology: OnlineFirst

In advance of being published in the print version of Lighting Research and Technology (LR&T), all papers accepted for publishing are available online. SLL members can gain access to these papers via the SLL website (www.sll.org.uk)

Teasing apart office illumination: Isolating the effects of task illuminance on office workers

A de Vries, JL Souman and YAW de Kort

Change of circadian effect with colour temperature and eye spectral transmittance at different ages

HJ Tian, T Chen, Y Hu, T Guan and MP Cai

The standardisation of light and photometry – A historical review

DR Bertenshaw