Spoilt for choice

Thanks to the recent advances in fluorescent lighting technology, specifiers now have considerably more choice in selecting the best luminaires for high and low bay applications.

When specifying light fittings for any application it’s clear that the specifier’s ultimate objective is to provide the end customer with the best lighting scheme, in terms of lighting quality, energy performance and ongoing cost of ownership. In order to do that, it’s important to stay abreast of changes in lighting technology so that projects always take advantage of the most recent innovations.

Lighting for high and low bay applications is a case in point. For many years the only sensible choice was high intensity discharge (HID) light sources such as metal halide and high pressure sodium but, more recently, that choice has broadened.

With the introduction of the T5 fluorescent lamp, along with fittings that have been optimised to take full advantage of their characteristics, light outputs that are comparable to HID sources can now be achieved with considerably lower energy consumption and a higher level of control flexibility. Consequently, I would recommend to all lighting specifiers that they take a fresh look at what can be achieved with T5 fittings.

To that end, it’s worth considering some of the performance characteristics of both types of source. For example, HID sources have a long warm-up time (as much as 15 minutes) so the frequency of on/off switching has to be minimised – and the majority of HID lamps can’t be dimmed. Clearly, this severely limits the control options that are available, as most energy-saving lighting control depends on being able to switch or dim the lighting whenever required.

In contrast to HID, fluorescent lighting will re-strike immediately and can be dimmed whenever needed, so there are many more control options. For example, in a warehouse these control strategies would typically include occupancy detection in aisles that are only used occasionally, so that lighting only switches on when a person or vehicle enters the aisle. Where natural daylight is entering the building the lighting can also be set to dim as appropriate to maintain the design illuminance.

Another key consideration is the installed electrical load and with high-output fluorescent fittings it is often possible to replace HID fittings on a point-for-point basis while reducing the installed load considerably. If we consider a 400W HID lamp with additional ballast losses of 60W, this can be replaced by a 4 x 40W or 4 x 55W T5 fitting, reducing the load from 460W per fitting to 160-220W (depending on selected lamps) with the added benefit of improved colour appearance and colour rendering.

Just as importantly, fluorescent lamps are available in a wide range of colour temperatures and colour rendering indices, so the specifier has more scope to get the lit environment just right for the activities in the space and the customer’s preferred ambience.

This train of thought was put to the test recently when we worked with supermarket chain Netto on ways to reduce energy consumption and improve lighting quality with minimum cost and disruption.

A number of options were considered and the best solution proved to be replacing the existing 400W HID lamps with 4 x 55W fluorescent fittings, using 4000K colour temperature tubes, on a point-for-point basis. These are controlled via integral occupancy and daylight sensors to minimise running hours and resulted in projected savings of around £50,000 per annum on energy alone. The ability to include integral emergency lighting in the fluorescent fittings also means there is no need for a separate emergency lighting system, as would be the case with HID lighting.

Further savings will be achieved through lower maintenance costs as the fluorescent tubes offer a life of 16,000 hours before re-lamping is required, compared to around 9,000 hours for HID lamps. The use of multi-lamp fittings also means that a single lamp failure will only have a minimal effect on light levels in the area and re-lamping can be scheduled for a convenient time. When single lamp HID fittings fail, light levels in a wide area fall dramatically so the lamp has to be replaced immediately to maintain a safe working environment.

In the light of all of these factors, which have been proven in the field at Netto and other companies, I would urge anyone involved in specifying high or low bay lighting to take a step back and consider the current picture, rather than relying on what’s always been done in the past. In that way, end customers are assured of a solution that takes full advantage of the technologies that are now available.

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