The full picture
March 1st 2008

Reducing the cost of ownership of a lighting installation involves more than simply choosing efficient light sources.

David Barnwell of Holophane Europe explains how understanding the full picture gives the greatest benefits

In the vast majority of manufacturing, processing or warehousing facilities, lighting accounts for a significant proportion of the running costs. And, as these costs come straight off the bottom line, it makes sense to take a close look at how to save money, energy and carbon dioxide emissions.

To that end it's necessary to consider more than the headline figure of lamp efficiency, though this is important of course. How the light fitting distributes the light and the way the lighting is controlled, along with features such as self-cleaning, all contribute to a lower cost of ownership.

This is particularly true of buildings with high roofs, where access to the lighting is difficult and disruptive, because maintenance makes a major contribution to overall cost of ownership. Anything that can extend re-lamping schedules, therefore, will help to save money. In addition, if lamps are disposed of less frequently there is less to pay on disposal within the requirements of the WEEE Directive.

These issues are crucial from the very first point of considering a new lighting installation or replacing an existing one. For example, in the majority of such cases the required light output – to make sure enough light gets to floor level from the high fittings – will necessitate the use of high intensity discharge (HID) lamps. This normally comes down to a choice between metal halide and high pressure sodium.

In the past the technology wasn't available to dim these HID lamps so, traditionally, the control aspects of the lighting weren't given much consideration.

Now, however, there is a system available to do this, so dimming has become an option – and a very important one at that.

Apart from saving energy, the ability to dim the lamps can extend their life and reduce maintenance costs as well.

To explain the benefits of dimming further, it's necessary to understand one of the key characteristics of HID lamps, namely that they take a while to warm up and reach full light output. And, if you switch them off they need to cool down for a while before they can re-strike. These characteristics have severely limited the control options available to buildings using HID lamps in the past. For instance, it wasn't practical to use occupancy sensors in warehouse aisles for switching lighting on and off, because of the time taken to come back on when someone enters the area.

Now that dimming is available, it's possible to dim the lighting in an area when there's nobody using it and, because the lamp remains on, the light output can be ramped up again immediately when it is needed. Thus, the problems of re-strike times are eliminated while also saving considerable energy.

In addition, many warehouses and factories have extensive roof lighting to let natural daylight into the space. In the past, the lighting would have remained on at full light output regardless of how much natural light was available, because of the time required to turn it back on if a cloud reduced daylight levels for a while.

Using a dimming strategy makes it possible to link the lighting to a photocell that measures the amount of light at floor level. When this level is exceeded because of natural daylight, the electric lighting can be dimmed to save energy – and, again, ramp up again immediately if it gets cloudy.

All of which saves energy, of course, plus it has the added benefit of extending the life of the lamps because they are being used less. This means that lamps do not need to be replaced as often, so all of the disruption and hassle associated with accessing high light fittings is reduced.

This includes downtime to erect scaffolding or bring in a cherry picker, as well as the paperwork associated with the latest Working at Height regulations.

These were all considerations for Schneider Electric when selecting lighting for an extension to its Warehouse and Distribution Centre at Telford. From previous experience, the company knew that lighting had the potential to make a significant contribution to running costs. In order to minimise these costs the warehouse was constructed with a large area of skylights to allow high levels of daylight into the space.

In order to take full advantage of the natural daylight, options for dimmable lighting were explored and Holophane's Prismatron system was selected for the project.

The warehouse area is divided into four quadrants for the purposes of lighting control, with a lux sensor in each quadrant, used to maintain an illuminance of 280-300 lux. The assembly area for control panels is divided into two sections, each with a lux sensor, maintaining illuminance levels at 400 lux.

Each of the lux sensors produces a 0- 10V control signal in direct proportion to the lux levels, sending the signal to a Schneider PLC building controller, which in turn communicates with the Prismatron dimmable ballasts. In this way, the lamps are dimmed or ramped up in direct relation to the lighting requirements of the space.

These examples illustrate the key principles of selecting a lighting system for a factory and warehouse, making the best use of the latest technologies. In parallel with these it's important to select light fittings with efficient optical performance to ensure light is directed to where it's needed and none is wasted. Some fittings also incorporate a self-cleaning feature that uses convection currents to remove dust, so that maintenance costs are reduced even further.

The important thing is to look at every aspect and, where appropriate, call in specialist expertise to ensure that no stone is left unturned when it comes to minimising cost of ownership.