While many companies, lighting specialists, and facility managers now use LED technology, it is not uncommon to see metal halide lamps in manufacturing facilities, big-box stores, industrial spaces, and warehouses.

And while these bulbs are more efficient than high pressure sodium lamps, they cannot hold their own against LED bulbs (especially when it comes to energy efficiency, cost savings, and light output). As more and more people become aware of this fact, they are changing to LED technology.

Two common questions we get asked by those looking to convert to LED technology are ” How many LED watts can replace 400 metal halide watts?” and “Can a 150-watt LED bulb replace a 400-watt metal halide bulb?

The second question is erroneous as you can never use watts to determine the light output of a LED bulb. We’ll talk about this in detail in the next paragraphs.

How Many LED Watts Replace a 400-Watt Metal Halide Bulb?

When buying a LED light, watts are not what you should be looking at; what you should be looking at are the lumens. Watts are not an indication of brightness, they only measure the amount of electricity a bulb draws.

Understanding Lumens and Their Role in Lighting

We usually buy things based on their quantity. When buying milk, we look at the gallons; when buying fruits, we look at the pounds. Buying light bulbs should be no different.

For the longest time, people bought bulbs depending on how much energy they consumed (wattage) and not based on the amount of light they produced. Watts measure the amount of energy a light source uses, they have nothing to do with brightness.

LED bulbs need fewer watts to produce a lot of light, which means wattage ratings are not as important as they were in the past. LED technology is all about creating bulbs that use less watts to produce more light.

Lumens measure the exact amount of light a bulb puts out. They are a more accurate way to measure light output because they tell you how the light performs, regardless of its source.

Most electrical professionals use foot candles to measure the levels of light in indoor and outdoor spaces.

What exactly is a foot candle?

It is a measurement of light intensity. It can be defined as the power of light discharged by a uniform light source on a 1-square-foot surface.

When lighting specialists want to measure the foot candles in a specific place, they use something called a light meter. This meter gives you the foot candle readings of the exact spot you’re in. If you happen to move closer to the light source, the foot candles will increase; if you move away, they will decrease.

If you stand between two light sources, the foot candles will be the joint lumen output of the two sources dispensed to where you’re standing.

Do lumens really matter?

They are the only thing that matter when replacing a conventional lighting system with LED technology. When getting LED fixtures, the most important thing you should look at are the lumens each fixture produces. If the initial lumens produced by each 400W metal halide fixture were 30,000, you should get LED fixtures that produce 30,000 lumens.

A metal halide light that produces 30,000 lumens discharges 75 lumens per watt. While the light may seem very efficient, it falls short when pitted against a LED light because there are LEDs that emit as many as 200 lumens per watt. There are also other things you need to be aware of.


Initial Lumens and L70

Lumen depreciation is one of the biggest downsides of metal halides. These lights lose their lumens very quickly and the quantity keeps rapidly decreasing from the first time they are used. If the initial lumens of a metal halide light are 30,000, the number could go down to 15,000 by the time it reaches half its lifespan.

The best thing about LEDs is that they work differently. LED manufacturers refer to the L70 rating when specifying the life of a LED. L70 is an accurate estimate of the time it takes for a LED to lose 30% of its initial lumens. This is usually given in the range of 50,000-100,000 hours and is usually mentioned as lumen depreciation or lumen maintenance. The L70 rating of a LED bulb is usually much higher than that of a metal halide lamp

Metal Halides and Light Loss

Besides suffering from rapid lumen depreciation, metal halides also suffer from light loss. Because the lights are omnidirectional, they discharge light in all directions. In order for them to produce the maximum amount of light, reflectors must be integrated into the fixtures housing them to redirect the light.

However, the problem is that even if the reflectors are efficient, a lot of lumens (up to 30%) will still be lost because of fixture absorption, spillage, and diffusion.

LEDs are directional and only generate light over a limited portion. This means more light reaches the targeted area because very little light is lost to absorption.

CRI and Its Effect on Light Quality

For those of you not familiar with CRI (Color Rendering Index), it is a measure of a light’s ability to reveal the true colors of objects compared to a natural light source. If a light is of high quality, it doesn’t need a lot of lumens to reveal the true color of objects. For instance, a LED light that emits 10,000 lumens may seem brighter than a metal halide light that emits 20,000 lumens.

Differentiating Between Photopic and Scotopic Lumens

While we talked about foot candle readings earlier, determining lighting quality is not as simple as taking these readings. Our eyes do not see light the same way light meters do.

For example, if a lighting specialist takes the foot candle readings of two light sources – a LED light and a metal halide light – and then asks people close by to say which light looks brighter, they may point to the LED light, whereas the light meter readings may show differently.

The human eye and a light meter perceive light very differently. The eye has two light-sensing cells located in the retina called rods and cones. Cones are more active during daytime and in well-lit environments while rods are active at nighttime and in dim  environments. Scientists refer to daylight vision as photopic vision and night vision as
scotopic vision.

Why is all this important?

Well, until recently, lighting specialists only measured photopic light, not considering that the light emitted by bulbs could appear differently (to human eyes) in the light and in the dark. Thanks to technology, there are now two ways to label the lumens a light source produces: by its photopic lumens and its scotopic lumens.

Since the human eye doesn’t see light the same way a light meter does, this can result in energy savings. The eye has the ability to see more light than what’s technically discharged as lumens. This means you can switch to a LED bulb with more scotopic lumens and see more light than you would from a metal halide light with a higher wattage. You can reduce energy consumption by using low-wattage bulbs that produce the same or higher-quality light.

Summing It Up

Throughout this post, there are three things we have been trying to emphasize. Metal halide lights are very bright when new but lose their lumens very quickly. LED light is focused while metal halide light is not. With LED lighting, no lumens are lost because of reflection You need fewer LED lumens than metal halide lumens to get the same amount of light – it’s a matter of quality over quantity

How Many Lumens Will Be Enough for Your Space

Photometry, the science of measuring light, is the best way to determine the amount of light you need in a space. But drawing upon our experience as LED lighting experts, we can tell you the average amount of lumens needed indoors and outdoors.

Generally, 15,000-25,000 lumens are needed indoors (in places like warehouses, auditoriums, and industrial spaces) and 14,000-20000 lumens are needed outdoors. But the exact number of lumens required will depend on the setting and the height of the lights.

LED bulbs are not equal, some produce more lumens than others (more than 150 lumens per watt). Always choose those that produce more lumens per watt as they will significantly lower your energy consumption.

Two Great Replacement Options

When it comes to replacing metal halide lights, there are two ways you can go: retrofitting or a full fixture replacement. If you choose retrofitting, only the bulb and ballast will be removed. If you choose a full fixture replacement, the bulb, ballast, and the light fixture will be replaced.

Deciding which option is better for you will depend on the current condition of your fixtures and your company’s needs and priorities. If the fixtures are old or damaged, they will need to be replaced. If they are fine, replacement kits are the best option.

Are Retrofit Kit LEDs of High Quality?

Yes. Just like new fixtures, retrofit kits contain LEDs of the highest quality. The only difference between the two alternatives is that retrofitting is cheaper because it is not as labor-intensive or material-intensive as a full replacement.

One way to ensure you buy quality retrofit kits is to buy from a reputable manufacturer. All our retrofit kits have a 10-year warranty and function optimally in both hot and cold environments.

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