When specifying LED lighting it is important to be aware of all of the factors that impact on the performance of the installation. Simon Miles of Carbon8lighting highlights the key issues.
lighting, which has now become the light source of choice for many commercial lighting applications. What is less known, however, is the fact that the latest generation of LED modules, coupled with luminaires designed specifically, are now delivering sufficiently high light outputs for many other applications. As a result, LED luminaires can now be specified with confidence for high bay and exterior lighting.
The popularity of LED lighting is largely the result of significantly improved energy efficiency combined with much longer lamp life, the latter having implications for maintenance and other cost of ownership parameters. In the case of applications with high roofs, such as factories, warehouses and retail ‘sheds’ – where access to luminaires can be challenging and disruptive – reduced maintenance requirements are particularly beneficial. The same is true for outdoor lighting, where access issues and the need to despatch maintenance crews is expensive. In addition, LED lighting will typically provide better quality light with improved colour rendering compared to the lighting traditionally used in these applications. In outdoor applications, whiter light with better colour rendering also engenders a feeling of security.
The key difference between traditional light sources and LEDs is that with LEDs, the wattage does not correlate to the light output. When selecting LED lighting, therefore, it is no longer meaningful to refer to the wattage of the lamps – the lumen output is what counts.
Thus, in the past when high or low bay lighting was upgraded it was essentially a matter of replacing like with like – 400W SON with 400W SON, for example. With LED light sources, the situation is not as clear cut and there is a real danger of over-lighting a space and wasting money.
uThe Discus Gen2 is an evolution of Carbon8 Lighting's successful Discus LED High Bay. The Discus Gen2 is designed for lighting large areas such as warehouses and factories, inside and out.
Also, in the early days of LED high/low bay fittings, which were typically achieving 80-90 lumens per watt, an industry ‘guideline’ developed for lamp replacement. This used a ratio of around 3:1 for calculating the wattage of an LED fitting that was replacing a traditional fitting. So, for instance, a 400W SON or metal halide fitting would be replaced with a 150W fitting producing 12,000 to 15,000 lumens.
In fact, this 3:1 ratio has become ingrained in the psyche, to the extent that many people
nyone who has even a passing interest in lighting cannot have failed to notice the rapid increase in popularity of LED
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forget they are buying light, not watts. The trouble is, the 3:1 ratio doesn’t take account of the higher lumen outputs of more recent LED fittings. Many people have become stuck on the idea that 400W HID fittings should be replaced with 150W LED fittings with no consideration of the actual light output. To give an example of high/low bay LED lighting has evolved, the 150W LED high bay fitting we introduced in 2015 produced just over 14,000 lumens. This was quickly superseded by a 120W high bay fitting, producing over 18,000 lumens. Now the latest generation is available in a 90W version that produces 16,000 lumens, while the 150W version delivers over 25,000 lumens.
So, to put this into perspective, if the 3:1 ratio is adhered to, then replacing a 400W HID fitting with a modern 150W LED fitting would provide around 40% more light than was actually needed. Not only would this waste a lot of energy, it would also ‘over-light’ the space.
Thus, in the example above, the 90W LED high bay would be a more suitable replacement for a 400W HID fitting, giving the correct light levels for that area whilst reducing energy consumption and costs. Further cost savings would be achieved through the simple fact that a 90W lamp costs less than a 150W lamp.
It is also worth bearing in mind that LEDs are directional, so that less of the light output is ‘lost’ within the luminaire. This means that luminaires designed to work with LED light sources can provide higher light outputs. This in turn means that required illuminance levels can often be met with a lower lumen output. Alternatively, depending on the nature of the space, it may be possible to use fewer luminaires to achieve the required light levels and distribution, thereby reducing both capital and maintenance costs.
Light source variation
It is particularly important to be aware that not all LEDs are equal in terms of light output, energy performance and lamp life. Thus, when specifying LED lighting systems the luminaire manufacturer should be able to provide the reassurance that their LEDs are high quality.
For example, there have been issues with poor quality LEDs exhibiting variation in colour temperature between individual light sources. This is because the way that LEDs reduce white light is quite complex. It actually involves using a blue LED that excites a phosphor coating and it is the phosphor that emits the white light. This means that the consistency and quality of the phosphors used is critical in ensuring consistent colour temperature. So quality control procedures that ensure consistent colour temperature are clearly important. A good indication of this is whether the manufacturer is able to state a precise colour temperature, rather than a range.
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While the focus of interest is often on the LED itself it is important not to lose sight of the role that the luminaire plays in optimising overall performance. As noted above, the optical design of the luminaire should be designed to take full advantage of the performance characteristics of the LED light sources. This can deliver significant performance improvements over and above those delivered by the inherent efficiency of the light source.
Just as important is the thermal management which, again, is highly dependent on the design of the luminaire. In fact, the long life of the LED light source that is so important in terms of maintenance costs is very dependent on good thermal management being incorporated into the luminaire. This will prevent the LED circuitry from reaching temperatures that would shorten the life.
Typically, good thermal management is achieved by including an aluminium heat sink in the luminaire that will conduct heat away from the sensitive electronics. There may also be additional design features that encourage convection of air through the luminaire to carry heat away from the heat sink.
Without a doubt, the right combination of LED light sources, luminaires and controls provides electrical specifiers with a perfect opportunity to help clients improve the quality of their lighting while also significantly reducing their energy consumption, carbon emissions and cost of ownership. The important thing is to be aware of all of the criteria that should be taken into account when determining the best solution.
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uA Carbon8 lighting installation at Harvest Foods.
difference between traditional light sources and LEDs is that with LEDs, the wattage does not correlate to the light output. When selecting LED lighting, therefore, it is no longer meaningful to refer to the wattage of the lamps – the lumen output is what counts.
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