Luminous flux differs from power (radiant flux) in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light.
Radiant flux measurements indicate the total power of all electromagnetic waves emitted, independent of the eye's ability to perceive it (See also our article called Scotopic vs Photopic Vision: How Your Eyes Perceive Light Quality).
Terms Commonly Used When Referring to Lumens
There are always terms relative to the industry that don't make much sense to the typical property owner, so I thought I would give you some of the more common terms related to Lumens. Here you go....
LPW – Lumens Per Watt. The number of lumens produced by a light source for each watt of electrical power supplied to the light source.
LUMEN DEPRECIATION – The decrease in lumen output of a light source over time; every lamp type has a unique lumen depreciation curve (sometimes called a lumen maintenance curve) depicting the pattern of decreasing light output.
For instance, a 400 watt metal halide depreciates nearly 70% in the first 3 years vs a comparable LED High bay fixture which depreciates 30% over 50,000 hours, one of the distinct advantages of LED lighting.
LUMEN MAINTENANCE – The deterioration in the amount of light that is emitted from a lamp over time. A lamp with a good lumen maintenance will emit a consistent amount of light over its lifetime, emitting as much as 90% of its original capability at the end of its lifespan.
A lamp with poor lumen maintenance will lose as much as 50% of its ability to emit light over time. The chart below shows the most common lighting sources and you can see how induction and LED have a much longer depreciation curve.
LUMINAIRE – A complete lighting unit which contains a lamp, housing, ballast, sockets and any other necessary components.
LUMINAIRE EFFICIENCY – The ratio of lumens emitted by a luminaire to the total lumens emitted from the light source within the luminaire.
LUX – A unit of illuminance equal to 1 lumen per square meter.
MEAN LUMENS – The average lumen output of a lamp over its rated life. Mean lumen values for fluorescent and HID lamps are typically measured at 40% of their rated lives.
INITIAL LUMENS – The lumens produced by a lamp after an initial burn in period (usually 100 hours).
(Source: www.maxlite.com)
How To Find The Lumen Output Of Your Existing or New Lighting
The only way to make sure that you will get the correct amount of light for the area that you intend to light is through a lighting layout.
A lighting layout will define the lumen output of your old fixtures and help to analyze new possibilities that give you the maximum amount of light while also saving money with your electricity bill.
We provide a FREE lighting layout and consulting (depending on the project) based on the opportunity to either supply or supply and install your new energy efficient lighting.
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