Lighting Efficiency
Into the
Improving lighting in the workplace has to be about more than increasing energy efficiency. We also need a ‘blue sky’ approach that focuses on emulating natural daylight, writes John Aston
T
he drive to reduce carbon emissions from lighting is intensifying, and yet few look beyond the savings gained in numbers to ask: ‘How is the reduction achieved?’ Not since
the late 1970s has there been such a focus on energy management in lighting; nor have there been so many companies offering solutions. But simply cutting the electricity used by your lighting poses real risks of ruining the design, and poor lighting may actually lead to much higher carbon emissions and additional business costs. Eighty per cent of our sensory input comes through
our eyes at work, and although lighting may well be using as much as 40 per cent of an office building’s electricity, it represents only a tiny fraction of a business’s costs. Using a quick-fix solution that spoils the lighting design might well lead to staff having to work longer hours because their effectiveness and concentration has been damaged. Any change to a lighting design must therefore be based on the idea that the right light is provided in the right place at the right time. Every time there is an energy crisis, cutting energy
costs becomes a priority. Popular quick fixes from the past have included the use of high-efficiency reflectors that suppliers claimed would allow the user to remove one lamp from a twin-lamp fixture. Customers were convinced by a light reading (lux measurement) taken immediately below the fitting without being shown how much light they had lost between the fittings. At present the lighting world is experiencing an
unprecedented technology change: the introduction of solid state lighting, or LEDs (light emitting diodes). The result is a plethora of information being projected
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at an unprepared market, without enough investigation into how the quantity or quality of light is altered. Big claims are being made concerning LED replacements for conventional fluorescent lamps. The present ‘state-of-the-art’ T5 high-efficiency
linear fluorescent luminaires are capable of delivering a system efficacy in excess of 80 lumens per watt (taking into account gear and optical losses). The very best LED solutions are achieving 60-65 lumens per system watt, and matching the colour rendering and consistency of a good fluorescent lamp can reduce this figure further. An apparently low-cost, ‘quick-fix’ LED lamp
replacement will almost certainly not be delivering such performance, so we must always benchmark against the best conventional lighting as well. The Lighting Industry Federation’s Technical Statement 41 is particularly pertinent and covers other matters such as product liability and electromagnetic compatibility. Of course, the real way to use new technologies like
LEDs to genuinely beat the old ones will be to develop new products to deliver the benefits most effectively. Initially, such solutions will be more costly to purchase but they may well have a lower whole-life cost. In addition, there is the danger that future legislation
covering the energy use of lighting might encourage the use of quick fixes by relying too heavily on basic efficiency numbers. The question of whether lighting design is an art or
a science is still debated; after all, the visual appearance of a lighting scheme is highly important. But as the Building Regulations develop, there is the danger that a desire to simplify the policing of such measures will lead to highly prescriptive rules – such as ‘you will use
Using a quick-
fix solution that spoils the lighting design might well lead to staff having to work longer hours
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May 2010 CIBSE Journal 39
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