Photometrics or Light Output
Simply put Photometrics are the various factors which determine performance of a light fitting to insure your getting the quality of light you require where you want it.
Photometrics include graphs diagrams and data so that lighting designers ,electricians and architects may determine the suitability of a luminary for various applications.
The specification most commonly used for evaluating and comparing the performance
of conventional lighting fixtures is lumen output. Technically speaking, the lumen is a
standard unit that measures the total perceived power of a light source output. ie volume
Just because a light fitting has a bigger lumen output than another fitting does not mean its better .
Conventional lighting fixture manufacturers often report total lamp lumens
more prominently than or instead of total fixture lumens. Because many LED
light fittings do away with the distinction between lamp and luminaire, only
total fixture lumens can serve as a basis for valid comparisons between LED and
conventional lighting fixtures.
▪ LED lighting fixtures and conventional lighting fixtures are tested differently, and
therefore some photometric data is reported differently. These differences must
be taken into consideration in order to accurately compare conventional lighting
fixtures and LED lighting fixtures.
▪ A fixture’s total lumen output does not account for wasted light. Because LED
lighting fixtures are essentially directional and naturally create white and
colored light without filtering or additional lensing . LED fixtures
typically waste much less light then their traditional counterparts, and deliver
more of their total light output to a target area. An LED lighting fixture
with lower rated lumens, therefore, may deliver the same or more useful light in
a specific application than a comparable conventional lighting fixture with a higher
rated lumen output.
Whats watts got to do with it ?
Because of incandescent light bulbs, most people are used to looking at wattage
to determine the light output of a light source: a 100-watt lamp puts out more
light than a 60-watt lamp. General service incandescent lamps use the same filament material heated to the same temperature, so the only way to increase their light output is to increase
the wattage. This is the main reasons why incandescent lamps are so inefficient.
LED light sources are much more efficient at converting watts to lumens. Different
materials can be used within the LED sources themselves, each of which has its own light extraction efficacy. For these and other reasons, two different LED sources can consume the same number of watts but differ widely in lumen output.Because watts can’t be used as an index of light output, evaluating the “brightness” of LED sources for a given situation requires you to think differently about lighting.
standard 60-watt incandescent lamp emits a total of about 800 lumens, but the light
is emitted equally in all directions. When you’re reading at your office desk, your book does not receive all 800 lumens from your desktop lamp, nor do you need it to.