The usual arrangement for lighting large outdoor areas such as car parks is to use a small number of high-mast lighting fittings. In the case of Birmingham Airport long-stay car park 1, however, the proximity of a runway means that it is impossible to adopt this approach. Instead, a much larger number of low-mast lighting fittings have to be used.

In fact, 180 fittings, each of which has a 70-watt SON-T high-pressure sodium lamp, are used to light the 500-space car park. This relatively large number of fittings made the car park a particularly attractive target for energy-saving measures.

To evaluate how effective such measures might be, Schneider Electric agreed to provide a trial installation based on its new Lubio lighting controllers. Three controllers were fitted, one master and two slaves, together with comprehensive metering and recording equipment from the company's Powerlogic range.

To make it easier to evaluate the performance of the Lubio installation, a switch was incorporated so that the Lubio controllers could be bypassed and the lighting fittings fed direct from the supply. All of the equipment was fitted in a feeder-pillar enclosure which was installed out of doors adjacent to the car park.
The Lubio controllers were configured to provide energy savings in two ways - by controlling the switch-on and switch-off times for the installation, and by regulating the voltage applied to the lamps.

Control over the on and off times was achieved using the astronomical clock built into the controllers. This computes the sunrise and sunset times for the location at which the controller is installed, and can thus accurately predict the time at which ambient light will need to be supplemented by artificial lighting. In addition, a light sensor is provided to turn the lighting on during unexpected dark periods, such as when heavy cloud is present. A further option is available for controlling the lighting via a building management system (BMS).

Regulation of the lamp supply voltage is a particularly useful way of achieving energy savings, as it offers the useful bonus of increasing the service life of the lamps. Prior to fitting the Lubio controllers, the lamps in this application were fed directly from the mains supply. Although this has a nominal voltage of 240V, records made during the trial revealed that it varied from 232.5V to 252.8V. The high voltage excursions are particularly detrimental to lamp life.

The Lubio controllers were set to provide a constant output of 220V during the car park's hours of peak usage, and 200V from 10:00 pm to 4:00 am, when the car park is much less busy. Direct measurement of the lighting levels showed that, even when operating at 200V, these were comfortably higher than the average of 30 lux and minimum of 10 lux specified in the Cibse fact file for outdoor car parks in urban areas.

It has been reported that, with the SON T lamps used in the installation, a 5% reduction in voltage is likely to yield a 33% increase in bulb service life. However, for a return on investment calculation, 25% is often assumed. In addition, the Lubio units provide ramp control over the voltage applied to the lamps, reducing stress and switch on and switch off, thereby further extending their lives. The result is substantial reductions in maintenance requirements and in bulb replacement costs.

The trials took place between January 2006 and August 2006. For their duration, the Powerlogic metering system recorded, at 30-minute intervals, information about voltage, current, power, power factor and total harmonic distortion, as well as active and reactive power. The information collected was subsequently analysed using Merlin Gerin System Manager software running on a PC.

The results are very interesting. With the Lubio system bypassed, the average energy usage over a 30 minute interval was 7.326kW, while with Lubio in circuit this fell to 5.665kW, a saving of more than 19%. The savings in reactive power were even more impressive at around 47%. Total harmonic distortion was also reduced by approximately a third on all three phases, and the power factor was held close to unity, except for short intervals while the lamps were starting up.

The overall results are summarised in the table below. The figure used for lamp life extension in this table is based on tests that Schneider Electric has carried out in France.
It is worth highlighting the net savings in the last two lines of this table, which show that the modest investment in the Lubio system delivers substantial and ongoing savings as well, of course, as helping to improve the overall energy efficiency of the lighting installation.
These benefits have proved sufficiently convincing for Birmingham Airport not only to retain the trial installation, after removal of the monitoring equipment, but also to consider other areas of the airport where Lubio lighting control could deliver benefits.

The trial carried out at Birmingham Airport with Lubio lighting control equipment from Schneider Electric has shown conclusively that it can deliver a whole range of benefits. These include energy savings, improved power factor and reduced maintenance requirements.
Further, the investment required to achieve these benefits is small and the payback period is short. Clearly, in this and similar applications, installing efficient lighting control is an excellent business proposition.