Light of day

Taking a piece of clothing to the window to see what colour it is, is still a feature of shopping but retail is waking up to daylight indoors, writes Francis Pearce.

‘People stay in retail environments longer when they have access to daylight; they are in a better mood and they spend more,’ says Mark Ridler, lighting director at architecture practice BDP. ‘The perception is that daylighting will give you energy savings in combination with lighting control but the main reason for using the two is that you can make money.’

Many leading UK retailers now specify rooflights ‘for all new build projects to ensure a high percentage of evenly distributed natural light within the interior,’ according to a soon-to-be released report by the National Association of Rooflight Manufacturers. It says that ‘in many situations sales tend to be better in naturally lit locations; colours are more vivid and true, making goods appear attractive and encouraging customers to spend more time in these areas’.

In 1999, research for the Pacific Gas & Electric in the USA that looked at 108 stores found those with skylights had 40 per cent higher sales than those without. Four years later, a second report concluded that natural lighting contributes to customer loyalty. The explanation could simply be that the naturally lit stores were newer and generally better designed, and therefore more inviting, but when customers were polled, most felt them to be cleaner, more spacious and more open.

Peter Van Der Kolk, the business development director of lighting controls company Helvar, says that the direction of light, colour temperature and overall illuminance levels in a space can have a notable effect on a person’s mood. ‘This does not mean that it is just the intensity of artificial light, but also the colour temperature that can have a noted effect when looking to increase a person’s alertness levels. This makes sense when you consider natural light as this in itself varies in terms of both intensity and colour temperature, not only over the course of the day but also in line with seasonal changes,’ he says.

‘In theory, all spaces would benefit from using daylight,’ says Cosmin Ticleanu, a daylighting expert from the Building Research Establishment. ‘It’s free energy and a healthy light source that renders objects in a natural manner. It’s also very important for staff and their mood and behaviour, which is reflected in service. Training is helpful but they also have to be in good mental shape,’ he says.

Not all lighting experts are entirely enthusiastic about daylighting in retail, though. ‘We have done a lot of daylight modelling to help a shopping centre in Ireland fine tune their daylighting and control heat gain from its huge glass roof,’ says lighting consultant Mary Rushton Beales of Lighting Design House. She is far from convinced that daylighting is a panacea. ‘Daylighting is excellent where you have food courts and shopping centres but it takes more thought to integrate daylight. There is a large department store near me that has what was hailed as a groundbreaking daylighting scheme but every time I go there they have added more localised artificial lighting. For retail space to be successful you need to highlight products. I think you can save more energy and gain more benefits in a retail scheme or shop with a really, really carefully considered artificial lighting scheme than with a daylight scheme.’

And many smaller stores remain in the dark about all forms of lighting. ‘When the BRE looked at 100 retail spaces around the Watford area we noticed the illuminances weren’t right. For example, there was a clothing shop with hanging rails where the circulation area had 1400 lux but the clothes were in the dark. Often, the overall lighting strategy might not be right, particularly in the smaller shops,’ says Ticleanu.

NARM has, however, been working with De Montfort University on issues such as the recommended minimum rooflight area needed to achieve a desired illuminance level, and the use of appropriate lighting controls to maximise the benefits of natural light via rooflights.

On a clear, sunny, summer’s day at noon, the light level outside can be 10,000 lux whereas you only need 1000 lux in a clothing or furniture shop to judge colours accurately. It takes 20 to 30 minutes for our eyes to adjust from broad daylight to complete darkness, so controlling the transition from light to dark and vice versa is an important part of lighting design, usually achieved by combining natural and artificial lighting. How ‘real’ colours look under artificial light depends on the source and its colour rendering index. Daylight has a CRI of 100 closely mimicked by halogen lighting (which is gradually being phased out by law, despite lighting designers’ protests), whereas an LED spotlight might have a CRI between 80 and 97.

Sweden’s Gothenburg Airport has a duty free store with a 1,000 sq m floor whose operators, the Nuance Group wanted the lighting to be energy efficient, help customers navigate and spotlight promotions. ‘Gothenburg Airport was one of the more challenging from a lighting point of view, as there was a large amount of natural lighting from the central atrium skylight as well as a suspended grid system ceiling,’ says lighting consultancy JPLD creative director, James Poore. The artificial lighting solution was designed around a family of fittings using Megaman’s LED AR111 halogen lamp replacement to save energy. ‘As well as significant energy efficiencies, the end result is a beautifully lit space that brings just the right level of drama and impact,’ says Nuance Group global head of shop design, Thomas McCrave.

Trinity Leeds, the 93,000 sq m retail scheme by architect Chapman Taylor is split over three levels. Its new build east mall comprises three distinctive arcades that flow from the streets to a large central space, lit primarily by natural light during the day. But sections of the arcades are covered by the levels above, making it necessary to manage the transition from a bright, sunny street to a relatively low ceiling height and then back to daylight under the dome. ‘You have to manage brightness and contrast issues, for example moving from a daylighting into a covered arcade or mall,’ says BDP’s Ridler. ‘At Trinity we deliberately put in a lighting system that managed that contrast during the day, but at night swapped round to something much softer. Controls are crucial where you are managing the transition between window areas with a lot of natural illumination to maximise the contribution of daylight rather than keeping everything on 100 per cent of the time.’

However, ‘small shops are undoubtedly the most difficult conditions for daylight because they tend to be long and thin and don’t have the opportunity to top-light because they have something else above them – often flats – but you also see the shop window blazing away in the middle of the day with no real benefit.’ The BRE’s Ticleanu agrees: ‘Retailers may be more interested in space for displaying product than worried about blocking the windows with shelving.’

Professor Paolo Di Trapani of the University of Insubria in Como, has developed an artificial skylight or window called the CoeLux, which reproduces the physical effects and optical phenomena of natural light using a combination of LED technology, sophisticated optics and nanostructured materials. It not only mimics the dynamism, direction and diffusion of sunlight but has settings for northern European, Mediterranean and tropical light, making it a potential solution – particularly for smaller shops – that could satisfy daylighting doubters and protagonists alike.

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