Energy Efficiency in Lighting


Areas where operating costs of organisations can be reduced are :

a) Lamps- Their Lighting efficiency

Low Pressure Sodium
This is the most efficient lamp type. These lamps may be familiar to us as the older yellow street lighting. Being monochrome lighting, it is impossible to discern any colour. These lamps are most suited to exterior lighting.

High Pressure Sodium
These may be familiar as the newer amber/yellow street lighting. While still a coloured light, it is possible to discern colours. The eye adapts to a degree to this lighting when it is the only lighting present and it looks more white over time. These lights are suitable for external lighting and for internal lighting when correct colour rendition is not important.

Metal halide and mercury vapour
Metal halide and mercury vapour lights are commonly used for high bay factory lighting. They give a bluish white light. Metal halide lighting is 25% more efficient than mercury vapour lighting.

Self ballasted mercury vapour
These lights can be distinguished by the lack of a control box or ballast and by the filament encircling the glow tube inside the larger glass envelope. These lights are considerably less efficient than metal halide lighting and their use should be avoided.

Fluorescent lighting
The above light types come in large wattages and are only suitable for high ceilings. For low ceilings, fluorescent lamps are the preferred type.
Older fat (40 watt) tubes have been superseded by thinner (36 watt) tubes. The thin tubes have an equal light output to the fat tubes and are the preferred type.
High efficiency triphosphor fluorescent lamps are available. These lamps give out 20% more light than standard phosphor lamps for the same power input.
Fluorescent lights have a ballast inside the fitting. (Usually this is rectangular object about 10 cm long inside the fitting.) These come in a range of efficiencies. High efficiency ballasts should be specified.
Fluorescent lights are available as standard linear lamps or as compact fluorescent lamps. The compact lamps can be used as a direct replacement for standard incandescent lamps. Although they are more expensive, they use five times less electricity and last eight times as long as fluorescent lamps.

Miniature dichroic down lights
Miniature dichroic lights (sometimes termed tungsten halogen or quartz iodide lights) are popular, visually pleasing lighting. They are often used in prestigious areas such as reception areas and show rooms. Their efficiency is inferior to fluorescent lighting and they should be avoided if energy efficiency is the prime concern.
Their life is significantly shorter than that of fluorescent lighting. This fact, combined with their lower light output and consequently larger numbers required to achieve the same lighting level means that their maintenance costs are significantly higher than for fluorescent lamps.

Standard incandescent lamps
The common incandescent light globe is popular because of its low purchase cost. The efficiency of these lights is low. They also have short lives which increases maintenance costs. The more efficient lighting types mentioned above should be used.

b) Lighting Controls and Levels

Lighting controls
The extra energy consumed by lights at switch-on is negligible. The only consideration in deciding how often lights should be switched on and off is the reduction in their life span from frequent switching. As a rule of thumb, lights should be switched off if they are not required for ten minutes or more.
This can be most simply achieved by encouraging people to switch off unnecessary lighting. There are a number of automatic lighting control methods which can be used.

Reset controls
Reset controls can be used to switch lights off at specific times during the day. The lights can then be switched on in the normal way. For these controls to be acceptable to users, the areas which are controlled and the times at which they are reset need to be decided sensibly. Switching lights off too often, at the wrong times, or in inappropriate areas can result in the system being unacceptable to users.

Occupancy sensing controls
Occupancy sensing controls can be used to control lighting. Ultrasonic or passive infra red sensors sense movement and switch lights off if there has been no movement in a zone for a pre-determined time. The delay time and the appropriateness for the area must be considered carefully if these controls are to be acceptable.

Daylight sensing controls
Daylight sensing controls can be used to dim or switch off lights in response to daylight levels.

One shot timers
These are commonly used in briefly occupied areas such as stairwells. One press turns the lights on for a pre-determined period.

Time of day switching
Time clocks can be used to turn lights on and off at specified times.

Appropriate lighting levels
Local task lighting can be used to raise local lighting levels. This lighting can be switched off when not required.