1. Lamp (Source) Efficiency Vs Fixture (System) Efficiency

Let's take a look at the information on a typical 400 watt metal halide bulb. While specifications may vary, a visit to a popular online website that sells Metal Halide bulbs shows that a brand new bulb has the following specifications:

• Color Temperature: 4000K
• Initial Lumens: 32,000 to 36,000
• Life Hours: 20,000

A recent white paper by the Dark Sky Society rated the mean lumens for a 400W Metal Halide to be 20,500 lumens and the rated life expectancy to be around 15,000 hours. But for purposes of this discussion, we will stick with the numbers we are familiar with. 

There is a lot of interesting information to look at. Initial lumens is a very high number, but in reality, a Metal Halide bulb starts off very bright and then drops its lumens rather quickly, settling in at a lower lumen output rather quickly. It is not uncommon to lose as much as 20% in the first 6 months alone. So while 36,000 lumens sounds impressive, within 6 months, it can be below 30,000 lumens. Lumen depreciation in a metal halide bulb is relatively quick. It is noted that at half life of the bulb, around 8,000-10,000 hours, lumen depreciation is already at 50%. 

Similarly, let's look at the operating nature of the bulb. A Metal Halide bulb is omni-directional. That means light is distributed in every direction. So it produces as much light horizontally parallel to the ground as it does facing downwards. 

To make this light useful, you need to gather it, collect it, and deliver it to where you want it. In fixture design, you add a reflector to do this job. The main problem with reflected light is how effective is the reflector getting the light that bounces off of it to the ground. A lumen that bounces off the reflector and bounces back into the fixture is considered a loss lumen. Anything more than one bounce is throw-away. As much as 30% or greater of the light can be lost in this reflective bounce. So if we do the math of a metal halide bulb in a high bay fixture, if we assume the initial lumens of the lamp at 36,000 lumens, after 6 months we would expect the fixture effective lumen efficiency to be: 

36,000 lumens - 20% (initial lumen loss) = 28,800 lumens 
Lumens loss from reflector bounce: 8,640 
Total lumens after 6 months in High Bay fixture: 20,160 

This does not take into account any lenses or shields that the fixture might already have. Keep in mind, this is bulb lumens, not fixture lumens, so anything else added that gets in the way of getting light to the ground will always take away from effective lumens.

Compare this to LED. If you think of a fixture, like LED High bay fixtures, or LED Retrofit Lamps that replace Metal Halide technology pieces, all the light is directional, in that, it is directed to where it is needed. Reflectors are not required. There is nothing to reflect. In terms of lumen depreciation, it does happen in LED, but it takes a lot longer for it to happen. For example, our LED retrofit kits have a L70 (lumen depreciation to 70% of initial lumens) of over 100,000 hours. So where as Metal Halide loses a lot of lumens in the first 6 months of life, LED tends to maintain its lumens for a lot longer. 

But there's more to this story, read below...  

2. Operating Life

As mentioned, the operating life of a typical Metal Halide bulb seems to be around 20,000 hours. Larger bulbs, like a 1000 watt Metal Halide, are around 15,000 hours. In terms of LED solutions, there are different ways suppliers describe the life of the product. One way is to mention L70. L70 is not a measurement of end of life, but it is a measurement of lumen degradation up to 70% of initial lumens. This does not mean the driver or ballast or some other component might fail prematurely. 

What we do know is the life of a Metal Halide bulb is around 15,000 to 20,000 hours. What we also know is that at half life, it has already lost 50% of its initial lumens. So while not dead, highly ineffective. For the record, it still consumes 400+ watts even though it is half as bright. 

Compare that to our LED Retrofit Kit rated at 100,000 hours (L70). So by the time the LED head reaches 100,000 hours, you have done 5 Metal Halide bulb replacements, possibly more.  

3. Efficiency (lumens/watt)

This is the pre-cursor to the next topic, energy savings, but the basic premise is the more efficient the bulb is, the more money you will save. So let's calculate the lumen efficiency of metal halide versus LED. 

To calculate lumen efficiency, you need to take the total lumens produced and divide it by the total watts consumed. In the case of Metal Halide, you also have to include ballast draw. If you recorded the total watts consumed of a typical 400W bulb, it is around 455 watts. The ballast consumes about 15% more energy over and above the bulb consumption. 

So calculating lumen efficiency for metal halide: 36,000 lumens / 455 watts = 79.12 lumens/watt. 

Let's compare that with our 150 watt LED Retrofit Kit: 23,250 lumens / 150 watts = 155 lumens/watt. Almost double of Metal Halide. 

And remember the golden rule: Efficiency Saves Money!  

4. LED vs Metal Halide Energy Savings

So in the above discussion, something important was pointed out. Above we talked about the mean lumens of a 400W Metal Halide to be around 20,500 lumens. Our 150W retrofit kit produces 23,250 lumens, but instead of burning 455 watts, it consumes only 150 watts. That represents a 66% savings in energy consumed to produce more light. But the truth of the matter, we think 23,250 lumens to replace 400W Metal Halide is over kill. For years, we have been selling our 105W LED Retrofit kit and it's more efficient replacement, the 100W LED retrofit kit at 15,500 lumens to replace 400W Metal Halide. Here is a recent example of a trial a customer did to make sure the lumen output of our 105W kit would be as good as what he was currently using. 

Notice: in the comparison picture below, the LED produces so much light it casts a  shadow from the pole in the light generated by the metal halide light. 

5. Savings on Maintenance

We have just as many customers wanting to convert to LED because of maintenance savings as they do for energy savings. Think about what we discussed, over the life of the LED retrofit kit, a customer would have to do 5-6 Metal Halide replacements. The higher the installation height, the higher the cost of replacement. And if you have a facility loaded with lights, this becomes a significant budget amount every year that you must take into consideration. Now, we know that reduced maintenance time on lights does not translate into dollars saved because it is highly unlikely that people will lose their jobs over the fact there is much less work to do. However, these people will have time to now work on things that matter, like fixing the machines that make the company money instead on replacing lights that cost the company money.  

6. Quality of Light

When you take a measurement of light with a light meter, it reads lumens. And this measurement of all the lights that contribute to the light at that location creates a measurement called foot candles. But let's think about that light that is being measured. Metal Halide creates all sorts of light, in all spectrum's, visible or otherwise. This includes UV and IR spectrum's, visible to the measuring device but not visible to the human eye. LED, on the other hand, does not produce UV and IR. Therefore, its readings using the same light meter is only picking up visible spectrum's. 

So there is a fun little test you can do. Have 2 light sources, LED and Metal Halide. And first ask, which one is brighter? And if the right LED source was selected, they should say LED. And then use a light meter, and the light meter may say the Metal Halide area is producing more foot candles. And so now you know part of the reason, but wait, there's 2 other pieces of information you need to know. 

One is called Color Rendering Index, or CRI. It is a measurement of Quality of Light. It's a scale between 0 and 100, 100 is excellent. And LED tends to have a high CRI value. So the other golden rule we say is "You need less quantity when you have more quality". Now, Metal Halide bulbs can be good, and are certainly much better than their High Pressure Sodium counterparts. But LED tends to be much better, so we perceive the light generated by LED to be brighter. More about this in the next section.  

7. Photopic vs Scotopic Lumens

Many years ago, even the discussion of photopic vs scotopic lumens was perceived as voodoo magic talk. There were those who believed in the difference and as many who discounted it. What this is is a discussion of how we perceive light (scotopic) vs how a camera or light meter perceives light (photopic). It is true people are able to see, and light is a big part of why we are able to see. Walk into a dark bat cave and you will quickly understand how important light is. Our eyes consist  of rods and cones, and how they work allows us to see colors and perceive objects at night. You will notice that it is harder to see colors in the dark. That is how our eyes work. Cameras and light meters work differently, they detect light in a totally different way, but what they do read they register and they interpret what it is 'reading'. 

Then scientists and physicists came along and they tried to make sense of all of this. And they came up with this concept of scotopic lumens. But then they took it a step further and decided to create a series of factors by light source of how lights really look to us scotopically versus how a light is measured photopically. What came out was a series of factors between 0 and 3. Some light sources effective lumens were reduced by these factors, like High Pressure Sodium. Some light sources were increased by these factors, like LED. What was determined was the factor associated with LED was higher than Metal Halide. So in the discussion above about perceived light, it helps to understand why we think LED Lights are brighter than other light sources, even though the light meter tells us differently. 

 

8. Rebates at time of purchase

Utility companies are trying to get their customers to convert to LED. Why? It's a matter of economics for them. Demand for electricity is growing, so once they reach capacity, they have to choices, build more capacity or reduce demand. Reducing demand is far more cost effective than increasing capacity. So the utility companies offer rebates to purchase LED. They want you to convert from Metal Halide. Every utility company runs their own rebate program but in general, there are some consistent processes and guidelines. For the most part:

• Utilities offer both prescriptive and custom rebate options. A prescriptive rebate is where they would say a 400W Metal Halide bulb is to be replaced with a LED bulb with these specifications. A custom rebate is for those exceptions not covered by prescriptive conditions
• Most LED products need to be DesignLights Consortium Qualified. This is a symbol of efficiency and performance. It is sort of the equivalence of Energy Star for consumer products. It tells the customer the lights are tested to a standard and has passed.

These rebates help reduce the cost of purchase and ultimately affect the quickness in pay back of the investment. With less cost at time of purchase, the time it takes to repay the investment goes down with the addition of rebate dollars. 

With Metal Halide, no rebates. Sorry.  

9. New versus Retrofit

So maybe at this point you are thinking that converting from Metal Halide to LED is a good idea. But this is where the journey begins. What to choose, what vendor to work with, new or retrofit. Think of the LED Market as the wild, wild west, and with every gun show there are the snake oil salesman trying to get you to buy their lotions. In the world of LED, there are many lotions, misconceptions and marvelous marketing ideals. For example, a well built LED Retrofit Kit will perform as well as a new fixture, and vice versa. It doesn't always make sense to replace the fixture, nor does it always make sense to retrofit a fixture.   

Conclusion 
There you have it, 9 highly backed up and legitimate reasons the fight of LED vs MH is no longer a fight. LED is a clear winner in every aspect of a light. We think of it as the perfect Metal Halide Replacement. 

Have any other reasons LEDs beat Metal Halide? Share them with us in the comments, we all want more reasons to go with LED over Metal Halide.