ENERGY REDUCTION SAINSBURY’S
rooflight that Hawker calls ‘daylight panels’. A lux meter on top of the product gondolas adjusts the artificial light levels by turning the lights up or down, or even off, in response to fluctuating daylight levels. For day-lit stores, light levels are set to maintain a constant 650 lux. For stores
without daylight, light levels are higher at 800 lux during trading hours. When stores are not trading, levels are reduced to 300 lux. According to Hawker, the only time when the lights are turned off completely is Christmas Day. In addition to daylight, Sainsbury’s is starting to achieve major energy savings from the use of LED lamps. It first started using them back in 2005 as a cost-effective replacement for fluorescent lamps in freezer cabinets. ‘Fluorescent light output dims by 75% at -20C so you need four times as much energy to match the lighting level,’ says Hawker, whereas LEDs are ‘agnostic to temperature’, meaning their efficiency does not drop off in the same way. Their imperviousness to cold also allows LEDs to be used in the stores’ big back-of-house freezers, in conjunction with motion sensors that turn them on and off. LED technology has moved
on considerably since 2005, with improvements in the lamps’ colour, cost and life span. Consequently, by 2010 Sainsbury’s was using LEDs in spotlights, in fridges, to illuminate counters and
Sainsbury’s first 100% LED store When it opened in January, the 3,700 m2
low-
energy store in Leek, Staffordshire, was the first Sainsbury’s to be fitted with a full LED lighting scheme on the main sales floor. Not only was it a first for Sainsbury’s but it was the world’s first commercial application of GE’s Lumination EL Series ‘blade’ LED luminaires. ‘The technology is straight out of GE’s research and development programme,’ says Hawker. The light fittings incorporate a linear LED unit. The most unusual aspect of the unit’s appearance, however, is its microlens light diffuser. This is attached beneath the lamps like a glowing, rectangular blade of light (see image above and next page).
The big advantage of the lamps is that the illuminated blades throw most of their light sideways. ‘The lamps illuminate the products on the shelving and not the shop,’ says Hawker. At a light level of 650 lux, the units delivered a 65% kWh saving when compared to a
28 CIBSE Journal August 2013
conventional high frequency T5 fluorescent lamp system. In addition to the shop floor, LEDs are also used in feature lighting, staff areas, refrigeration cabinets, sales counters and the bulk-store area, which is fitted with passive infra-red detectors to sense when the room is occupied. The store is even fitted with LED car park lighting, which incorporates very white LEDs. ‘Because the LED light is so white, it means that you can illuminate that space using lower lux levels, which saves us further energy,’ says Hawker.
Other carbon-saving measures in the store
include daylight panels, CO2-based refrigeration plant and a 520kW Uniconfort biomass boiler. The impact of all of these innovations is a 55% reduction in operational carbon performance and a 59% reduction in kWh for the store.
freezers and even to light its car parks. This year, the retailer has opened its first store with a shop floor lit entirely using LEDs (see box left). And it is investigating a number of new LED products, each with a payback of between two and three years compared to fluorescent technologies. Hawker says the switch to LED technology will require Sainsbury’s to change the way it thinks about warranties because the lamps are expected to last for eight to 10 years: ‘It means we need to deal with companies that will still be around in eight years or so for the warranty to be valid.’ He thinks the way Sainsbury’s buys
light fittings will change too: ‘If I buy an LED-based luminaire that will last for eight years, will I be able to upgrade the body and reuse the LEDs? And if I do, will the manufacturer reprocess the fittings?’ Hawker’s team is contacted on average
by three new lighting suppliers each month, all looking to have their products specified by Sainsbury’s. If the teams like
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