Taking LEDs to the max

As well as offering improved energy efficiency and reduced maintenance costs, LED lighting opens the doors to a number of opportunities for improving the quality of lighting. Neil Parrott, Design Manager with Riegens, explains.

LED light sources are certainly getting a lot of exposure at the moment, much of it focusing on their energy saving potential, as well as the reduced maintenance costs due to long lamp life. Many of the projects cited have been hospitality venues where halogen spotlights have been retrofitted with LED lamps or office and retail projects where LED luminaires have been used for general lighting.

However, it’s also important to be aware that LED lamps, and luminaires optimised for use with LEDs, open up a whole range of lighting possibilities that are impractical or difficult to achieve with traditional light sources.

Mimicking natural daylight

A very good example of this is the ability to create a dynamic lighting system that changes with seasons and time of day. This is something that has been achieved with limited effect in the past using different colour temperature fluorescent lamps and adjusting the proportion of light output from each. LED technology, though, enables the creation of a ‘tunable’ dynamic white light system where colour temperature can be varied between 2700K and 6500K, in combination with different lux levels.

This advance in lighting has great significance. It is now well accepted that the natural changes in light that occur through the day and through the year have an impact on our health and sense of wellbeing. Furthermore, several studies in recent years have confirmed the positive effects of artificial lighting to support this circadian rhythm. These effects manifest themselves in reduced accident risk, improved concentration and productivity, better visibility and a general ‘uplift’ in how we feel.

There is also a lot of evidence to suggest that dynamic lighting in hospital wards can improve health outcomes for patients.

The dynamic LED lighting used to create this system uses specially designed boards to deliver optimum control of white light. The boards provide high performance along the black body curve with colour rendering of Ra>80. They can be controlled by using either a DMX or DALI solution that can be programmed to follow a time schedule or to use different scenarios that can be selected manually in different areas. The result is greater comfort and a better environment for the user, offering high quality visual mimicking of the rhythm of sunlight.

Of course, as well as creating a dynamic and responsive lighting system, the use of LEDs reduces lighting energy consumption, while the extended life of LEDs reduces maintenance cycles.

Lighting as a system

The concept of dynamically changing lighting also highlights the need to think of LED lighting in a slightly different way. Traditionally it has been common to think of a luminaire as a collection of components that work together and, in an ideal situation, enhance the overall performance. The whole should be greater than the sum of the parts but often hasn’t been in the past.

LED lighting needs to be thought of as a system, where the whole is very much greater than the sum of the parts. For example, the performance of the LED light sources – in terms of light output and longevity – is strongly influenced by the temperature of the LED chip. If the temperature isn’t controlled effectively, light outputs will be reduced and the lamps will fail earlier.

In this respect, a luminaire that has been optimised for use with LEDs will play a key role in the thermal management of the system. Typically the luminaire body will incorporate structures to conduct the heat away from the LEDs and dissipate it into the surrounding air.

This has important implications for how we talk about the efficacy of luminaires. Traditionally the Light Output Ratio, or LOR, of a luminaire is used to quantify the amount of ‘useful’ light leaving the luminaire in relation to the total amount of light produced by the light source(s) inside the luminaire.

With LED luminaires the LOR is meaningless as the light output of LEDs cannot be measured freely. They need to be cooled to provide optimum performance and, as noted above, in most cases the whole luminaire acts as a heat sink to take heat away from the LED chips. Therefore, in providing a direct measure of the useful light produced by the luminaire against the amount of energy consumed, rated luminaire efficacy is a more meaningful figure.

Controls also become part of the overall system as LEDs are highly controllable and present many opportunities for optimising performance through enhanced control. The dynamic lighting described earlier is a clear example of this but more prosaic control strategies, such as daylight linking and occupancy control, are greatly facilitated by LED lighting systems.

Taking control to new heights

As the light output of LED lamps has improved the range of suitable applications has increased dramatically. In particular, the latest generation of LED lamps, housed in the right luminaires, now deliver lumen outputs required for high bay lighting. This provides an opportunity to greatly improve the quality of lighting in a wide range of applications using high bay lighting.

For example, the lighting in bus depots typically uses high pressure sodium lighting, which is not conducive to optimum visibility where large vehicles are manoeuvring. Similarly, the lighting in factories is important for detail work, while good colour rendering is important for colour-coded picking in warehouses.

In parallel, using LEDs enables levels of control that have not been possible with the high intensity discharge (HID) lighting traditionally used in high bay applications. Historically the key limiting factor has been the inability to dim HID light sources – though dimmable versions are now available – but if these are turned off to achieve maximum energy savings there is a prolonged warm-up period before the lamps return to full light output. This also has clear implications for health and safety in the event of a power failure extinguishing the lighting.

LED light sources can be dimmed and they will come on instantly when switched on. This makes it very easy to control them in various ways. For instance, many ‘shed-like’ structures have extensive roof lights to permit entry of natural daylight. So dimming the lighting in relation to daylight is an obvious measure.

In warehouses there is often considerable energy wastage due to lighting being left on in aisles that aren’t used for long periods of time. Using LED lighting provides an ideal opportunity to use presence or absence control to switch off lighting in unoccupied aisles, secure in the knowledge it will come on instantly when someone enters that aisle.

In summary, LEDs bring a host of new opportunities for anyone involved in lighting design. The important thing is to understand the possibilities – and then exploit them to the full.

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