Lighting economist Dave Tilley considers the options for retailers who will have to improve the energy performance of their lighting systems or, quite literally, pay the price

It has been predicted by government and various industry forums that demand for energy will outstrip supply by 2014 or 2015. Some predict an even earlier date.

So without significant reductions in energy consumption over the next two years, the price of energy will increase by over 20 per cent, particularly in the commercial sector.You only have to look at the upward trend of oil prices and the impact on petrol prices caused, in part, by the reduction in supply.

Soaring prices are not enough to make consumers consume less energy, so the only other method of control is legislation. The lighting industry has been subject to numerous energy fees, taxes and regulations – all with little impact.

Slices of reality

Given these stark slices of reality, why do retailers still insist on lighting sales space with relatively inefficient lighting, minimal controls and light levels, on average, of 1,000 lux?

To illustrate the point, I shall use a retail warehouse.

Most retail warehouses have three layers of lighting: daylight, high bays and display lighting. Daylight enters through skylights, and the level of daylight is often adequate to illuminate the sales area. High bays are 400W architectural or industrial fittings that provide bright ambient light with uniform distribution. Display lighting tends to be ceramic metal halide (CMH), and provides extra illumination for specific displays and particular areas.

The layers of lighting tend to compete.

We must ask ourselves two questions. Is there an alternative to the 400W high bay? Will retailers be more energy efficient without legislation?

An example

Take an actual retail warehouse as an example (the brand and location must remain confidential). The sales area is illuminated by the following luminaires:

  • 154 400W high bay luminaires – a total of 310,000kWh (including gear loss) every year
  • 40 70W CMH track spotlights – 11,760kWh

Total annual energy consumption is therefore

321,760kWh, representing carbon dioxide emissions of 178.25 tonnes.

Replacing the 400W high bays, point for point, will result in the following:

  • 154 4 x 80W Intel luminaires (T5 fluorescent with daylight saving) – a total of 210,000kWh a year

The baseline saving is 100,000kW, about 32 per cent, and 55.40 tonnes of carbon dioxide emissions are prevented.

However, it is worth noting that at a height of five metres there is a significant variance in average lux levels (see Table 1).

Now, retailers will argue that the average lux level from the 4 x 80W Intel, 617 lux, is not enough to sell products. Before we consider that argument, it is worth examining average lux levels when the same Intel fitting is suspended at a height of three metres (Table 2).

The increase is relatively small at six per cent, but will 650 lux be enough to maintain sales at current levels? The key point has little to do with direct energy comparisons. The 4 x 80W Intel with daylight linking will spend a minimum of 30 per cent of the time either off or at 10 per cent light output.

Daylight allowance

If a daylight allowance of 30 per cent is included in the energy calculations, the annual energy saving increases to 163,000kWh (53 per cent, equivalent to 90.30 tonnes of carbon dioxide).

It is therefore reasonable to assume that skylights will enable adequate light, even at the high lux levels currently specified by retailers. Perhaps the focus should be on the capture of daylight, in tandem with controls for artificial lighting.

Another question for retailers: ‘If CRI is so important, why not use more daylight, which has a perfect score?’

On to the 70W CMH track-mounted spotlight. If you ask a retailer why they add this third layer of lighting, they will probably offer the following reasons:

* To highlight products or a specific area.

* To draw out the colour and texture.

* A particular area needs it.

* To aid customer movement and navigation around the store.

OK, the retailer wants to create contrast, drama and customer movement. There is nothing wrong with this ambition, but is it really necessary to introduce a third layer of light that will have to overcome the existing light?

There is of course an argument for reducing ambient light and using display lighting as the primary lighting. Imagine that natural light is augmented with intelligent ambient lighting controlled to deliver an average of 250 lux. Product is illuminated as required depending on product type. For example, CMH on textiles and perhaps LED on hardware.

The energy saving is significant – potentially 70 per cent. Sales will be maintained, possibly increased, because daylight has a perfect colour rendering index and the store’s ‘green’ credentials will be self-evident.

Enforced change

Realistically, retailers have to rethink light levels, controls and natural light, or they will be forced to change by high energy prices, legislation, taxation and, ultimately, fines.

There are examples of retailers trialling efficient stores but little evidence that the ideas used will become the norm, or that ageing retail stores will be made more efficient. Legacy estates may be the Achilles heel of many retailers in the future.



The verdict is not a straightforward one. Circumstances in retail stores are very different. However this does not mean that retailers should ignore the opportunities provided by daylight, lighting controls and technology. The business climate is changing at a rapid rate, and retailers must embrace the change or pay the price.
Office job

Are those efficient office lighting schemes you read about in magazines like Lux really achievable in the real world? Yes, says lighting economist Dave Tilley, with some caveats

Showroom showcase

Times may be tough, but a new lighting scheme rather than a simple retrofit should pay dividends beyond simply cutting your electricity bills. Dave Tilley explains