As a guide:

• Incandescent and tungsten halogen are very good
• Polylux Deluxe fluorescent lamps are excellent
• Lucalox is only suitable for non-discriminatory areas

Ra is a relative measure on a scale off 0-100 of how good the colour rendering of objects will be. The higher the number, the better the performance. This term is also called Colour Rendering Index (CRI) From the lamps with suitable light output and colour rendering select the highest efficacy. If colour rendering is not critical, select Lucalox followed by metal halide, fluorescent and mercury. If colour rendering is important then the best choice if Polylux Deluxe followed by Polylux and metal halide lamps. Tungsten halogen may be considered but remember the low efficacy will impose high operating costs. Note that if, in the example above, the use of lighting is increased to 5000 hours per annum (about 14 hours per day) then the economic figures are changed to:

• Return on investment: 22%
• Payback: 4.6 years

This example has been specifically chosen to show that usage is just as important as installed load when considering savings. However, electrical load can be easily calculated, but usage is usually a casual under-estimate. A more accurate value can often be ascertained by asked when the lighting is switched OFF, rather than when it is ON. Lamp Efficacies Lumens per Watt SOX 200 Lucalox 130 MultiVapor 100 Fluorescent 94 Mercury 60 Incandescent/ Tungsten Halogen 20

To determine the number and wattage of new lamps required the safest and easiest approach is to use a one-for-one replacement plan. In some cases you may want to consider fewer luminaires with lamps of higher light output, thereby reducing the capital investment. Always seek advice from a lighting engineer as such changes can adversely affect the light distribution across the space and also increase the risk of glare from the installation. Luminaire selection has two steps:

• The space is not occupied
• There is adequate natural daylight available
• It is outside normal business hours