This blog post is our second post to one of our most popular posts, “How Many Watts does it take to replace 1000W Metal Halide”. While many of the concepts are the same, there are some important differences between 400W and 1000W Metal Halide.One of the most common questions we get asked is:
“How many LED watts does it take to replace a 400 watt metal halide bulb?” “I just talked to another LED company and they said to use their 150W LED Fixture. How much is your 150W LED Fixture?” “I’m looking to convert my fixtures over to LED High Bay Lights and what wattage should I get?”
Probably the best advice we can give anyone is never buy a LED product based on watts, buy it based on lumens and then figure out how little watts you can use to make those lumens.
What is a lumen?
In simple terms, it’s a measurement of light that basically defines how much light a certain fixture or bulb produces. It is essentially the light you are replacing. Fixtures produce lumens, consume watts, and all the fixtures lumens combined provide a foot candle measurement. When we do a photometric calculation, we take the scientific information associated with that fixture or bulb, insert it into photometric software, and calculate the foot candles for the area. In real terms, a light meter will give you a foot candle reading at the place you are standing. Move close to a light source, the foot candles will rise. Move away, it will fall. The foot candle reading in between 2 fixtures is the collective lumen output of the 2 fixtures distributed to that point where you are standing.
Why does this matter? A lot more than you may think, because it’s all that matters when it comes to replacing old lighting systems with new and improved lighting technology.
When replacing an existing fixture (or entire system), you need to know your lumen output per fixture. Let’s say your metal halide fixtures initially produce 32,000 lumens per 400 watt bulb. So instead of thinking, “I need 400 Watt LED to replace 400 Watt Metal Halide,” you need to be thinking
“I need an LED that can replace 32,000 lumens.”
With this example of 32,000 lumens for a 400 Watt metal halide, that means it is outputting 80 lumens per watt (initially). In the world of lighting in today’s technology world, this isn’t that efficient, with LEDs approaching 200 lumens per watt. However, there are some other factors going on here that you need to be aware.
Understanding Initial lumens and L70
32,000 lumens seems bright. It is. However, bulbs were designed for high initial output because Metal Halide suffers from
pretty fast lumen depreciation. It is not uncommon for a metal halide bulb to lost 50% of it’s lumens at half life. Full life for a metal halide bulb is 15,000 hours. That means at 7500 hours of use, it has lost half (or 16,000) of its lumens.
L70 is a term the number of hours before a bulb is performing at 70% of initial lumen output. For metal halide, that calculates to 5,000 hours of use.
You will notice L70 times for LED is spoken in terms of 50,000 and 100,000 hours, not 5,000 hours like it is for Metal Halide bulbs.
Loss of Light due to Reflection
LED light is directional, that means all its light is delivered where it is pointed. It does not need a reflector to collect it and deliver it to where its needed. Conventional light sources are omni-directional and require reflectors to gather the light and focus it to where it is
needed. Any reflection of a lumen that is over 1 bounce in the reflector is effectively a loss of that lumen. It has been proven that you can lose up to 30% of the effective lumens in this reflective process.
So if a Metal Halide bulb has 32,000 initial lumens, the loss accounted to reflected lumens drops the lumen output to around 20,000 lumens.
Quality of Lumens – CRI
Color Rendering Index, or CRI, is the best explanation in comparing the quality of light source. Simply said, the higher the quality of light, the less quantity you need. It is not uncommon to have customers tell you that 20,000 lumens of LED appear brighter than 60,000 lumens of other light sources, like HPS.
The basic truth is you need less quantity when you have higher quality.
Photopic vs Scotopic Lumens – How we perceive light versus how a light meter perceive light.
Photopic lumens are lumens that are detected by a device, like a camera or a light meter. It picks up all sources of light that we cannot see, like UV and IR. Scotopic lumens are lumens detected by the human eye. Its how we as people perceive light.
LED produces light within these spectrum’s, which means the light perceived by LED is light that we use. It is rare to see a LED light produce IR or UV spectrum’s. These wavelengths are invisible to people, so they have no value to us from a vision perspective.
It is not uncommon to stand under 2 light sources, one LED and one not, and first read the fc measurement with the light meter of both light sources. And then ask individuals standing near by what light source they think looks brighter. And have the one that looks brighter contradict what the light meter tells us.
We perceive light sources and brightness different, in some cases, than light meters.
Putting This All Together
The basic takeaway from all of this is you need far less LED lumens than metal halide or HPS lumens.
- Metal Halide bulbs are very bright out of the box, but not so much even after only 6 months of use.
- LED light is directional. The light goes where it is needed. No loss due to reflection.
- LED light is high quality light. You need less quantity when you have higher quality.
So how much LED Lumens do you need?
Only a photometric can tell you exactly how much you need. But over almost 10+ years of selling LED lighting, our general rule of thumb is:
- Indoors: 15,000 to 25,000 lumens (depends on application and mounting height). You would find these lights in a warehouse, factory, gymnasium, auditorium or swimming pool.
- Outdoors: 14,000 to 20,000 lumens (depends on application and mounting height)
By searching for a LED equivalent to a 400 Watt Metal Halide you can easily find fixtures that output at over 100+ lumens / watt. Especially when you go with quality products from reputable companies, you can reach higher than a 150 lumens / watt output. This will allow you to cut your wattage usage per fixture by 2-3 and sometimes 4 times which will prove to save substantial amounts of energy when you start talking about replacing multiple fixtures.
What are my “Replacement Options”?
Replacing can consist of two things: retrofitting or fully replacement. The difference is simple, a retrofit kit is just like replacing the light source (bulb and ballast) in the fixture. On the contrary, full replacement includes replacing the entire fixture including bulb and ballast. Which is best for you? That really depends entirely on your facility, fixtures, needs, and priorities. In general, if your existing fixture shell is good to use and not outdated or falling apart, a retrofit kit will work perfectly. If they are old, outdated, leaking or need replacing: a full replacement is probably the best option.
Are the LEDs in a retrofit kit as good as a LED fixture
Yes. Despite of what you heard or been told, there is no reason to think or believe that a retrofit conversion kit won’t perform
or last as long as a new LED fixture. Retrofits don’t always make sense, but they do if you have a significant investment in your fixture or the look of your fixture. Our retrofit kits are warrantied for 10 years, and they have been extensively installed inside a closed sealed fixture in hot locations, like Arizona, Nevada, California and some even in the Middle East.
Keep this in mind: retrofitting is almost always cheaper because it’s easier to do and it’s not as material intensive as a full replacement is (but that is obvious). So if you can retrofit, go with that over a full replacement!
It is possible to replace a metal halide fixture, that of any wattage (30 on up to 1000+), with LED technology. It can be as simple as retrofitting your existing fixtures or a little more work intensive to fully replace, but both will work.
So although it may seem hard, confusing, or expensive: the benefits far surpass of these common scares that people have when making the consideration of upgrading to a new luminary technology. An investment in LED will provide payback in many ways, from less energy usage to higher quality of light that they produce.