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Maximising savings with LED lighting

Published:  08 September, 2017

When LED lighting was first introduced it was restricted to a narrow range of applications where the energy and maintenance saving benefits could be combined with relatively low light outputs. Several generations of LED later, and with significantly increased light outputs, those same benefits are now available in applications requiring high levels of light. These include high bay and low bay lighting in factories, warehouses and other ‘shed’ type buildings, as well as floodlighting of building exteriors and other outdoor spaces.

The appeal of LED lighting is largely due to the significantly improved energy efficiency combined with much longer lamp life, the latter having implications for maintenance and other cost of ownership parameters. This is particularly important in high roofed buildings because access to luminaires can be challenging and disruptive. Thus, reduced maintenance requirements are especially beneficial.

The same is true for outdoor lighting in areas such as car parks and around loading bays, where access issues and the need to despatch maintenance crews is expensive.

Unsurprisingly, therefore, many owners and operators of such facilities are keen to upgrade to LED lighting. Typically, this will involve replacing high intensity discharge (HID) light fittings, such as high pressure sodium or metal halide, with LED fittings.

In addition, LED lighting will generally 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.

In new installations the process is relatively straightforward but when upgrading from an existing HID installation to LED it’s essential to understand the key differences between these light sources. Equally, it is important to be aware of how LED light sources have evolved in recent years.

Lumens not watts

The key difference between traditional light sources and LEDs is that with LEDs the wattage does not correlate to the light output. With LED lighting , therefore, it is no longer meaningful to refer to the wattage of the lamps – the light (lumen) output is what counts. For instance, when high or low bay lighting was upgraded in the past it was usually 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.

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.

However, this 3:1 ratio is no longer valid because it doesn’t take account of the higher lumen outputs of more modern LED light sources and luminaires. Unfortunately, many people have become fixated on this ratio and the idea of replacing 400W HID fittings with 150W LED fittings. This approach gives no consideration to the actual light output – losing sight of the fact that the purpose is to deliver light, not watts.

This issue is clearly illustrated by a lighting upgrade project carried out by Carbon8 at Etex Building Performance’s facility in Bristol. Here, the company had initially been evaluating our first-generation high bay LED luminaires, replacing failed 400W SON fittings with 150W LED fittings.

As a result of the savings achieved during this initial evaluation the company decided to replace the 500 remaining 400W SON fittings with LED in both the production and warehouse areas. In the interim, however, we had launched a second generation (Gen2) of high bay LED fittings. A key difference between the two is that the first generation 150W fittings, launched in 2015, produced just over 14,000 lumens. The Gen2 fittings are able to produce over 18,000 lumens with a power input of just 120W.

This enabled the 400W SON fittings to be replaced with 120W LED fittings, resulting in annual cost savings of nearly £140,000 and CO2 savings of over 1.8 tonnes per annum.

Also, there is now a 90W version of the Gen2 fitting that produces 16,000 lumens, while the 150W Gen2 version delivers over 25,000 lumens.

These advances also put the 3:1 ratio 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 is actually needed. Not only would this waste a lot of energy, it would also ‘over-light’ the space.

Light where it’s needed

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 light 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.

Luminaire choices

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. In particular, the optical design of the luminaire should be designed to take full advantage of the performance characteristics of the LED light sources – rather than just being ‘tweaked’ from a traditional HID fitting.

Enhanced control

One of the key constraints on optimising energy efficiency in the types of application described above has been the limited control capabilities of HID light sources. In contrast, LED lighting is highly controllable and this opens the door to many opportunities for improved control that will avoid energy being wasted.

These control options include presence detection, so that lighting in unoccupied areas can be dimmed, and dimming in relation to the levels of natural daylight entering the space.

At Cardiff Galvanizers, for instance, existing 400W metal halide floodlights were replaced with 180W LED Multifunction floodlights. This reduced the annual operating costs per floodlight from £266.53 to £111.57, with a return on investment of around 2.5 years.

Moreover, the success of this project led to the installation of 100W LED floodlights mounted on pylons in the main loading area and 150W LED high bay luminaires in the galvanizing control room. In the case of the loading area, the company is now able to take advantage of natural daylight levels, using photocells to switch the lighting off when there is sufficient daylight.

A key benefit of controlling LED lighting in this way is that when the lights are switched back on they provide full light output in an instant – compared to the slow warm-up required for HID light sources.

Summary

Without a doubt, upgrading from a traditional high bay/low bay lighting installation to LED luminaires will deliver significant energy and cost benefits. The key to maximising these benefits is understanding how LEDs differ – and taking full advantage of those differences.