Specifier be aware

It’s probably true to say that the owners of high intensity discharge (HID) lighting installations have been losing out over the last few years, compared to those organisations that are using other types of light source. This is because the enhanced control options that are now almost standard with newer fluorescent and other lamp technologies have not, until recently, been available for HID lamps.

This situation has changed, though, with the introduction of advanced electronic control gear for metal halide lamps, which enables them to be dimmed down to 10% of full light output and then ramped up to 100% without delay. So whereas in the past lighting specifiers may not have considered including occupancy and daylight controls for HID systems, they can now do so.

The reason for the historical lack of control options is that older HID lamps, such as metal halide and high pressure sodium, could not be dimmed – and there is a warm up delay when switching them on and off. Consequently, the tendency has been to turn them on at full output when the building is occupied and leave them like that until they are switched off again when the building is vacated.

Clearly this is wasteful of energy as there are many situations where HID lighting is used in areas of variable occupancy or at times when lower lighting levels are acceptable. For example, in a warehouse where aisles are only occupied occasionally through the day the lighting can be controlled on an aisle-by-aisle basis. So when the aisle is unoccupied the lighting is dimmed down to 10% and then raised to full output as soon as someone enters the space. The same principle can be applied in manufacturing areas where assembly teams move from one area of the factory to another.

Another obvious application of dimmable HID light sources is in retail sheds, where it is now very easy to establish different lighting scenes for different activities. This approach ensures that when customers are present the light levels are optimised to enhance the shopping experience, but then can be reduced when staff are cleaning or re-stocking.

Nor does the control strategy need to be limited to occupancy and the visual requirements of particular tasks. Many ‘shed type’ buildings, whatever their function, have extensive rooflights to maximise the natural daylight entering the space and this can often be sufficient to maintain design illuminance levels. Typically, though, there has been a reluctance to turn the lighting off in case a passing cloud reduces daylight levels temporarily and illuminance levels are rapidly reduced.

Now, of course, the lighting can be dimmed to the appropriate level, using a photocell to balance the contribution of natural and artificial light while maintaining illuminance levels and minimising energy consumption.

In addition, these principles need not be confined to internal spaces as HID lighting is also used extensively in loading bays, car parks and other external areas. So there is every reason to extend the benefits of improved lighting control to these spaces as well. For instance, in a school during the winter (or for an evening event), the car park and roadway lighting can be ramped up to full output at the end of the school day to accommodate the high traffic levels. At other times the light output can be reduced to save energy while maintaining safe lighting levels. The same principles can be applied to factory car park lighting during a shift change, and many other applications.

If saving energy wasn’t enough of a reason to specify dimmable HID lighting, there are also potential savings in cost of ownership as the latest electronic control gear will also extend lamp life. Given that HID lighting is usually mounted quite high, re-lamping often involves specialist access equipment so it is time-consuming and disruptive. It also generates considerable paperwork in relation to the Working at Height regulations. So an extended re-lamping schedule brings considerable time and cost benefits.

Furthermore, upgrading existing lighting is usually a quick win, in terms of return on investment through cost savings. So this has particular appeal to those organisations that have limited financial resources but still want to reduce overheads.

In the light of these developments and the benefits they bring it’s clear to me that dimmable HID light sources have the capability to bring a whole new layer of energy saving potential to many buildings and outdoor spaces. So it is vital that specifiers make their end clients aware of these opportunities and the potential for reducing carbon emissions and the total cost of ownership.