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
Anyone who has even a passing interest in lighting cannot have failed to notice the rapid emergence of LED lighting, that has now become the light source of choice for many commercial lighting applications. However, what is less known 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. This has important implications for visually demanding tasks such as assembly and picking. In outdoor applications, whiter light with better colour rendering also engenders a feeling of security.
As a result of this growing popularity it is inevitable that electrical specifiers will find themselves increasingly involved in the specification of LED lighting systems for these types of applications.
Indeed, the incentive for larger organisations to implement energy-saving initiatives is likely to be further fuelled by the new ESOS regulations. This Energy Savings Opportunity Scheme requires all organisations that are classified as ‘large undertakings’ to assess their energy use and the potential for energy reduction. They must also submit evidence to the Environment Agency.
The ESOS definition of a ‘large undertaking’ is an organisation that employs more than 200 people, or has an annual turnover in excess of €50 million and balance sheet assets exceeding €43 million. Clearly, many companies operating in the industrial, logistics and retail sectors will fall within the remit of ESOS.
Whilst ESOS will not compel such organisations to introduce energy-savings the process of gaining a better understanding of their energy performance will certainly highlight potential areas for improvement. A thorough energy audit, as required by ESOS, will also provide sufficient information to calculate the potential return on investment of any initiatives to improve energy efficiency. As lighting upgrades typically provide a ‘quick win’ compared to, for example, investing in new HVAC plant, the business case for such upgrades will usually make commercial sense.
Clearly, any such initiatives that impact on lighting will require input from electrical engineers. It is therefore important to fully understand all of the characteristics of such systems, from the choice of light source through to luminaire design and how the system will be controlled. All of these issues should be discussed in detail with any potential suppliers in the early stages of the specification process.
The key difference between traditional light sources such as incandescent or fluorescent and LEDs is that with LEDs the wattage does not correlate to the light output. When specifying LED lighting, therefore, it is no longer meaningful to refer to the wattage of the lamps – the lumen output is what counts.
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.
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.
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.
One of the key constraints on optimising energy efficiency in the types of application described above has been the limited control capabilities of light sources such as metal halide and high pressure sodium that are typically used for high bay lighting.
In contrast, LED lighting is highly controllable and this opens the door to many opportunities for improved control that will avoid energy being wasted.
In a warehouse, for example, aisles between racking are often unoccupied but remain fully lit throughout the day. By using simple occupancy sensors, LED lighting can be configured to dim or switch off in unoccupied areas and then ramp up to full output as soon as the presence of a person or fork lift truck is detected. This is something that could not be achieved with standard high intensity discharge lighting because of the warm-up period required for these lamps.
Similarly, many of these shed-type buildings have roof lights that allow significant levels of natural daylight into the space. LED lighting can very easily be linked to photocells to dim the artificial lighting in line with the levels of daylight entering the space, thereby maintaining illuminance levels with minimum energy consumption.
The benefits of enhanced controllability can also be applied to exterior lighting. Traditionally, outdoor lighting using metal halide or high pressure sodium light sources might be switched on and off by photocells but that would usually be the limit of the control that could be applied.
With LED outdoor and amenity lighting the level of control can be more sophisticated. For example, the light levels can be aligned to different activity levels at different times of day. In a pedestrianised area with coffee shops and restaurants, for instance, the lighting might be on at full light output until around midnight then dimmed to a percentage of full output for the rest of the night.
The important thing here is that LED lighting offers a great deal of flexibility in terms of control, so that the exact control strategy can be precisely tailored to the requirements of each project.
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.