LED Lighting Outshines Metal Halide

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.

When it comes to energy usage, LEDs outsave Metal Halide

Replacing metal halides in a commercial setting with LEDs is very easy to justify, especially as the installed costs of LEDs have come down just in the last few years, while their efficiencies have improved.

Metal halide lamps start out with fairly high lumen output, but depreciate in output quite quickly. In fact, the lighting output begins to decline just as soon as you turn on the power to the new bulb.  When it gets to 40% of its rated life, the metal halide has lost somewhere in the range of 30-40% of light output, and as low as 40% of its initial lumens by the end of lamp life.  

According to Pounds, The trick for design engineers with metal halides is not to measure around initial lumens, but at that 65% which is commonly called design lumens.

By contrast, LED sources  fade very slowly over time. Well-designed LED lighting fixtures can retain 70% of their initial output up to 100,000 hours, depending on operating conditions and other factors. At 24 hours per day of continuous use, such fixtures can deliver useful light for eleven years or longer — five times as long as metal halide sources.

Combine that with the fact that there are no lumen fixture losses with directional LEDs (as opposed to up to 30% with metal halides), and it’s easy to see why specifiers can replace an equivalent 400W metal halide with an energy-efficient 130W LED.

The benefits of this are obvious, especially as commercial energy costs are not coming down anytime soon.   By eliminating two thirds of the energy usage and doing the same with 130 watts as 400 watts, that savings would add up pretty quickly.

Energy Savings

Energy cost calculations based on 12 hours a day / 5 days a week @ .11 per Kwh
400w Metal Halide
130w LED Energy Consumption
Metal Halide Annual Energy Cost $164.74
LED Annual Energy Cost $44.62

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