LED outshines Metal Halide
When it comes to lumen output; all lumens are not distributed equally.
If you compare the raw lumen output of metal halides with the lumen output of LED lighting fixtures, it often seems that LED fixtures come up short. Such comparisons, however, are inaccurate and misleading, as they fail to account for the significant amount of wasted light in HID/metal halide lighting solutions.
According to ‘The LED Lighting Explained’ book, by Phillips, “lumen output is a poor measure of the suitability of a lighting fixture for a given task. A better measure is delivered light — how much light a fixture delivers to a surface or area, as measured in lux (lx) or footcandles (fc). You can make accurate comparisons between metal halide and LED lighting fixtures on the basis of delivered light, as it measures how much of a light source’s raw lumen output reaches a surface or area you want to illuminate. “
To determine how much of a conventional lamp’s raw lumen output reaches a task area, you must discount any light lost in the fixture housing (often over 30%), as well as any light lost as a result of lensing, shading, and filtering.
There’s even a new BUG standard published by the Illuminating Engineering Society to address this
issue. BUG stands for “Backlight”, “Uplight” and “Glare.” “B” stands for backlight, or the light directed in back of the mounting pole. “U” stands for uplight, or the light directed above the horizontal plane of the luminaire, and “G” stands for glare, or the amount of light emitted from the luminaire at angles known to cause glare.
Since metal halide lamps emit light in all directions, you must further discount any light emitted in a direction away from the target area (i.e. BUG).
And since LEDs are inherently directional, they emit almost all of their light output in the desired direction, rather than dispersing it in all directions.
“Think of the LED as a flat plate”, said Richard Pounds, SE Regional Sales Manager Eiko Global LLC. “The light is all from the bottom end. It’s all focused on the work plane with no fixture losses.”
In other words, that’s how a 30,000 lumen rated 400W HID source is equaled by a 12,000 lumen 130W LED.