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Lamp efficacy is defined as light
output per watt of input lumens per watt. Higher wattage lamps of each type tend to have the best
efficacy:
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SOX low pressure sodium lamps rank
highest with nearly 200 lumens per watt
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Lucalox high pressure sodium lamps
rank second with about 130 lumens per watt
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Metal halide lamps at 100 lumens
per watt are third, closely followed by fluorescent lamps at 94 lumens per watt and then mercury
lamps at 60 lumens per watt
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Incandescent and tungsten halogen
lamps are by far the least efficient at 20 lumens per watt. Specific values for lamp type vary by
lamp wattage
Fluorescent lamps may also vary by
lamp colour. Lamp Wattages The range of lamp wattages is important because of bearing on the range
of lighting levels obtainable
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Incandescent lamps have the widest
range - 15 to 1000w
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Fluorescent lamps have an upper
limit of 125W for European control gear although there is 215W American Powergroove version
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Mercury and high pressure sodium
lamps are available up to l000W
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Metal halide lamps go up to 2kW,
but the higher ratings are normally only used for floodlighting
Lamp Life Lamp life is not usually
a major consideration for energy efficient lamps - most have rated lives of 20,000 hours or
more
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Mercury, up to 24,000 hours and
Lucalox high pressure sodium lamps, up to 28,500 hours have the longest lives
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Multi-Vapor and metal halide lamps
range from 6,000 to 20,000 hours
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Fluorescent lamps have a very good
life - 5,000 to 18,000 hours, depending on type and control gear
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Incandescent lamps range from 1,000
to 3,000 hours. Lumen Maintenance Most lamps emit less light as they age
The rated life is an average figure
for physical failure when a replacement would be required to provide continuity of light. For most
lighting installations there is a minimum lighting level for safety and efficient use of the space.
With many lamps they are changed at this point and do not reach their rated life. This is sometimes
called the economic life. It does not normally have a specific quoted value as it will depend upon
critical factors which will vary for each installation
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Tungsten halogen and Lucalox lamps
have good lumen maintenance and so their economic life will be close to the rated life
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Polylux XL fluorescent lamps have a
much better lumen maintenance than standard or special colours
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Mercury and metal halide lamps have
a marked loss of light through life and so careful consideration of the economic life is
necessary
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