Energy Efficient Lighting

1. Efficient light sources such as T8 fluorescent, metal halide and soon LEDs.

The efficiency of light sources is measured in lumens/watt. Low Energy Lighting would generally produce more than 40 lumens per watt. A very efficient source could be defined as one with 80 lumens/watt or more of light output. However most of the very efficient lamps require some form of driver or ballast, which also has some electrical loss that needs to be included. After this is taken into account, actual power consumptions of different light sources can be compared.
They range from 0.3 lumens/watt for a candle's flame, 6-15 lumens/watt for standard domestic tungsten bulbs, 15-25 lumens/watt for most halogen lamps, 40-75 lumens/watt for compact fluorescent bulbs, and around 60 lumens/watt for LEDs.

The most efficient linear fluorescent lamps are up above the 80 lumens/watt threshold. These are mainly the linear T8 (22mm diameter tubes with electronic ballast) and some T5 fittings (miniature 15mm diameter tubes; those designated HE are better) Some high wattage CFL lamps, such as 55w TCL/PLL from Osram/Philips, can also make the grade. The old type T12 linear flourescent fittings with 1.5 inch (38mm) tubes and heavy wire-wound ballasts are less efficient; typically around 60 lumens/watts. So, there are many fluorescent lamps falling significantly short, especially the CFLs.

Metal halide lamps can achieve over 80 lumens/watt, when run off the more expensive HF ballasts. They are most often used in shops, but in a house, a metal halide fitting can be very effective at brightening up a large room during the day, during dreary winter conditions.

A peculiar feature of LEDs is that they run more efficiently when underpowered. This is a useful feature in a battery operated torch, allowing the batteries to continue giving reasonable light long after the battery power starts to fade. But the same peculiarity allows manufacturers to make exaggerated claims for various mains powered LED products based on laboratory performance; they may claim efficiencies of up to 140 lumens/watt. However at this level of efficiency the lamp might be running at half its normal power, and not be bright enough to be useful under real life conditions. LED technology is progressing rapidly though, and it may not be long before that kind of efficiency is produced by an LED lamp under normal working conditions.   

The ballasts or drivers of most low energy light fittings are not compatible with ordinary dimmer switches. If dimming systems are available they will be expensive, difficult to source and may be prone to malfunction. A better approach is to incorporate a variety of lighting into a room. Different combinations of ceiling lights, wall lights and plug in floor or table lamps allow for a choice of ambience.

2.Lampshades and light fittings that do not waste light and direct it where needed.

Once the light has been generated it needs to be delivered effectively. Lampshades can prevent a dazzling effect to the eyes, but they also block the light. Some fittings waste light within the fitting itself through poor design or materials. Other fittings emit light ineffectively through inefficient optics and lampshades. The ability of a light fitting to emit light is measured in Light Output Ratio (LOR) - typically an efficient fitting would have a ratio at least above 0.6, and probably above 0.7, meaning that 70% of the light from the lamp leaves the fitting.

The LOR has another element to it as well, because the light may be emitted in different directions that have an impact on its effectiveness as a source of light. An "uplighter" lamp fitting has an upward LOR (ULOR) which requires the light to be bounced or reflected from a ceiling or wall, before the target surface below is illuminated. In contrast a downward LOR (DLOR) is capable of lighting a surface directly. Downlighting (DLOR) is accorded an effectiveness rating twice that of uplighting (ULOR).