Actually, Toronto is now working on converting their overhead area lighting to LEDs from a company that is using the CREE XR-E.
If you investigate further, you'll find many of the Metal Halide bulbs (and others) actually degrade quite quickly.
These high output power LEDs from OSRAM, CREE, LumiLEDs are typically rated in the 50,000 to 100,000 hour lifetimes- to 70% output, instead of the 50% output often found in bulbs. This is quite different than your grandpa's LED, which degraded quite rapidly, as these new LEDs have thermal resistances below 10 C/W, instead of 250-350 C/W found in the old 5mm LEDs. They also solder the die to the substrate, instead of using epoxy, which helps tremendously.
One of the issues with Metal Halide is that once you get them in a fixture, attach a ballast, and all that jazz, is you can easily end up in the 50 something lm/W range.
An example of a high bay setup, is shown here, and compared with other sources:
**broken link removed**
There are high end ballasts, that can help a bit with the efficiency issue, but usually, to get top end Metal Halide efficiencies, you are looking at a 400 to 500 Watt light, where the 100W ones can be as low as 80lm/W, before you take account for significant losses in the ballast and also the fixture.
Metal Halide degrade significantly in their output over their short 20-30k hour lifetime. Expensive ballasts can also help a bit with this, but they don't help the VHO or HO types that much (the ones that top the efficiency lists). Some of the bulbs drop to ~50% output at 30k hours, and often drop by 40% in as little as 12k hours- high end ballasts can help here, but again, they don't help much with the VHO and HO. This drop in output in such a short time drops you into the 50lm/W range pretty quick, before other losses, like the fixture and ballast. Metal Halide bulbs usually also contain significantly more mercury than even the old fluorescents do.
Additional costs occur for bulb replacement by maintenance crews.
Many of the Metal Halide bulbs shift color over their life, but some advances have been made here.
Even a number of the 400W Metal Halide bulbs suffer from lower CRI, 65. With a ballast+bulb of 83lm/W, this drops to 54 lm/W by 12,000 hours, and continues to drop over it's lifetime. There are some high end specialty bulbs that hold up better now.
The fixtures add additional losses on top of all of this.
There is a chart that compares some of the various brands of Metal Halide bulbs here:
https://www.electro-tech-online.com/custompdfs/2007/03/UPSS_O-Rated_comparison.pdf
Some typical light drop over life curves for Metal Halide:
https://www.electro-tech-online.com/custompdfs/2007/03/LM_at_a_Glance_0805.pdf
Notice how the lower wattage bulbs, which you'd use in a low bay setup, have rather short lifetimes of 10,000-15,000 hours. They also have lower lm/W numbers...
The problem is that folks will often pick out the very best bulbs they can find, picking the best lm/W from one, the best CRI from another bulb, and then not consider ballast losses, and also very significant fixture losses (they can easily hit 50% loss, but there are some that are a bit better). Then they will pick out the very best lifetime bulb from another bulb, and use the highest initial lumen bulb for their lm/W.
Unfortunately, reality is often another situation.
For a low bay install, have you a good 100W bulb that stands out head and shoulders above the rest, and could you link a datasheet? How about ballasts that go with this particular bulb? And fixtures with specifications for losses?
I'd sure like to know what the cat's meow is in Metal Halide these days, when you look at the complete system (bulb, ballast, fixture), as I have an area that could really use an efficient lighting setup, but once I look at reality, the numbers keep ending up abysmal. So, if you have any recommendations, I'm certainly all ears!
I'd also be interested in any bulbs that are made for shorter runtimes, as if you only turn the typical MH bulbs on for 1.5 hours, their life drops by 60%. This would result in a 10,000 hour rated MH 100 or 125W bulb ending up with a 4,000 hour lifetime.
They also recommend that you re-lamp the fixtures at 60% of the rated life, since the bulb lm/W drops so rapidly, and due to their color shift. I'm told that some ballasts can help with this also, but again, apparently it does not help much with HO or VHO bulbs much.
If I do this, then the 10,000 hour bulb that ends up at 4,000 hours when you have them on for 1.5 hours, I end up having to replace the bulb every 2,400 hours.
One of the Metal Halide bulbs a local home store carries is the M175U.
Spectral output graph:
**broken link removed**
Lumen Depreciation:
**broken link removed**
CRI:
65
Average rated life:
7,500 hours
CCT:
4200
Initial Lumens:
14000
Mean Lumens:
9100 when mounted vertical
8200 when mounted horizontal
Mean lm/W:
52 lm/W when mounted vertical
46.8 lm/W when mounted horizontal
And this is for the bulb only! Not counting ballast or fixture losses!
Reality can be brutal at times, when you do not look at things from a system standpoint.
Fluorescent bulbs also have plenty of short commings, and one can even purchase a special energy star labeled fixture, and end up with a system that is only doing 30 lm/W when all is said and done...
Even Wal-Mart is in the process of converting a few stores with an LED product from Gel-Core which is only doing ~30lm/W (low efficiency LEDs for current state of the art in the market, which are in the 70-90lm/W for high power parts, and even higher for low power parts).
The massive US-based retail chain will install LED lights in 500 stores, saving $2.6 million annually in energy costs.
Wal-Mart Stores is to deploy LED lighting from GELcore in low- and medium-temperature refrigerated display cases in over 500 U.S. stores. The retailer expects that energy cost savings of a 500-store retrofit -- one of the top energy-saving initiatives that it will pursue in 2007 -- will exceed $2.6 million annually.
Of note:
"In stores where the new GE LED products will be put to work, Wal-Mart expects to net up to 66 percent energy savings, compared with incumbent fluorescent technology."
And
"The combined environmental impact of a 500-store installation represents an annual 35-million pound reduction of carbon dioxide emissions. It also equals the good that comes from planting over 4,464 acres of trees or removing over 3,143 cars from the road for every year the LED lighting operates in place of fluorescent lighting."
http://ledsmagazine.com/articles/news/3/11/16?alert=1
Related stuff:
-Folks prefer LED lighting:
"The lighting within the display case was much more uniform with the LED lighting system compared to the traditional fluorescent system. The results from the human subject experiment show that subjects strongly preferred the display case with the LED lighting. Considering the luminous efficacy of white LEDs presently available in the marketplace, it is possible to develop a LED based lighting system for commercial refrigerators that is competitive with fluorescent lighting system in terms of energy use. The LED based lighting would provide better lighting than traditional fluorescent lighting"
http://www.lrc.rpi.edu/programs/solidstate/completedProjects.asp?ID=52
See page 44 for the scores:
**broken link removed**
From GelCore:
"Primary benefits of GE’s RoHS-compliant, UL-approved LED Refrigerated Display Lighting solution include:
• Improved product visibility with reduced light-source glare on products and floors
• Hidden light source provides better access to products for stockers and consumers
• More robust and better for the environment than fluorescent lamps because it doesn’t contain glass or mercury and it doesn’t produce UV or infrared light
• Up to 78 percent energy savings compared with VHO fluorescent lamps in a 5-door fixture
• Over two times the life of fluorescent lamps in a cold environment reduces maintenance costs and hassles (50,000 vs. 18,000 hours)
GE’s LED Refrigerated Display Lighting solution also saves watts by lessening the load on the compressor. For every light watt reduced in a frozen food case, the compressor works less hard, saving ~ 0.45 watts. On a 5-door case, the additional energy savings from a reduced load on the compressor, can reach 70 watts vs. T8 fluorescent; 134 watts vs. HO fluorescent; and 330 watts vs. VHO fluorescent."
http://www.gelcore.com/literature/GELcore_WalMart_refrig_announcement_DE_FINAL_111406.pdf
The product that is utilized:
**broken link removed**
And on top of it all, the LEDs they are using don't have very high efficiencies!
1280 lumens/41 Watts = 31.22 lm/W
http://www.gelcore.com/literature/RefrigSpecSheetWEB7_7_06.pdf
Also to consider with fluorescent lamps, most don't realize the large losses in fluorescent fixtures, plus the additional losses in the ballast, that cause the usable lm/W to drop quite significantly, from what everyone runs around touting. Additionally, in this case, the cool environment also comes into play, which benefits LEDs. But with fluorescent lamps it requires extra power input into the fluorescent bulbs to keep them warm, which also loads down the refrigerator cooling system, for even more losses.