Voltage optimisation – the issues

The light output from any lamp degrades over time, (i.e a new lamp is brighter than an old lamp). In the case of Sodium (SON) lighting, for example, you can expect to see a 35-40% reduction in light output after about 18,000 hrs (2-2½ years). To counteract these ever diminishing light levels, initially the work area has to be over lit by typically 35-40% in order to guarantee a minimum light level requirement, after an acceptable period of time. This over lighting is achieved by either increasing the number or wattage of the light fittings in the first instance, so increasing the energy consumption of the lighting system. Voltage optimization not only flattens the degradation curve providing higher average lux levels over time, but prolongs the life of lamps and fittings and therefore reduces maintenance costs

A common practice for many companies is to replace lamps as they fail. Therefore there are always a large number of lamps in the system which remain lit, but are producing perhaps only half their original output, and are still consuming the same amount of electricity as a new lamp, which I suspect is now the case in some areas.

There are two factors, which need considering when determining the timing of lamp replacement, the change in light output and the probability of lamp failure. The relative weight given to these two factors depends on the lamp type.

Mains and low voltage tungsten filament and tungsten-halogen lamps usually fail before the decline in light output becomes significant. Therefore, the replacement time for these lamps is determined by the probability of lamp failure alone. All the other light sources, conventionally used, show a significant reduction in light output before a large proportion fail. Therefore, for these lamps, both the decline in light output and the probability of lamp failure are important in determining the lamp replacement time. Frequently it is desirable to replace such lamps even though they are still operating electrically, simply because the light output has fallen to an uneconomic level.

For the majority of installations the most sensible procedure is to replace all the lamps at planned intervals. This procedure, which is known as group replacement, has visual, electrical and financial advantages over the alternative of 'spot replacement' e.g. replacing individual lamps as they fail.

• Visually, group replacement ensures that the installation maintains a uniform appearance.
• Electrically, group replacement reduces the risk of damage to the control gear caused by the faulty operation of lamps nearing the end of their life.
• Financially, by arranging that the lamp replacement is associated with luminaire cleaning, and doing it at a time when it will cause the minimum of disturbance to operational requirements, the cost of maintenance can be minimised. Group replacement is an appropriate procedure for routine maintenance, and the frequency with which the procedure is carried out will have a direct bearing on the degree of energy reduction that is possible from the proposed ECO-MAX control system.

Obviously there is a cost implication to group re-lamping and cleaning of luminaries on a planned basis. However, the increase in light output gained by re-lamping can then be used to provide you with an energy saving which will far out weigh any additional maintenance cost incurred. By combining relamping with voltage optimization, we can usually provide excellent energy savings, and increased lux levels.

Applying higher supply voltages to your lighting systems increases the initial light output from a lamp but dramatically speeds up its degradation. Conversely, the ECO-MAX system by optimising the applied voltage in a controlled manner slows this degradation. The ECO-MAX system therefore trades a proportion of this increase in light levels to gain an energy saving.

Despite the possibility of having to replace any tired lamps that are producing less than 30% of their as new light output, controlled voltage optimisation reduces the energy consumption of your existing lighting systems by around 25%, without having to switch off or replace a single light fitting.

Whole site voltage optimisation

Discharge lighting is very tolerant to substantial drops in voltage supply, so large percentage savings are available, and indeed there are many benefits other than just energy saving, as detailed above. Due to the large amount of varied equipment that may be present on a given site, and their requirements, whole site voltage optimization can only achieve a lower percentage level of savings, although sometimes, of a larger load depending on your equipment profile. So if your lighting system is not that large, and you are struggling to meet a required payback with our Lighting Optimiser, then it would probably be worth looking at your total load from a whole site optimiser perspective. GWE's ECO-MAX Whole Site Optimiser is based on the same market leading core technology as the ECO-MAX Lighting Optimiser, and as such all our usual equipment and savings guarantees apply. Please see our Whole Site Optimiser section on the Products Page.......and remember, even if whole site voltage optimization is already in place we can usually get further substantial savings from the lighting.

Click here - Voltage optimisation Explained