Too bright is as bad as too dim. Trying to find that just right solution can be daunting. Luckily, we’re here to help.
“How many (LED) watts do I need to replace 250 watts metal-halide?”
“Another company said I need 75 watts to replace 250 Watts Metal Halide. How much is your 75 Watt LED?”
These questions are all to common. Customers thing in terms of WATTS to replace Metal Halide. Unfortunately, watts is actually the end point, and not where you should start. In this post, we will try and simplify this process and give you some guidance on how to come to the right solution.
What LED Wattage Replaces 250 Watts Metal Halide?
Rule 1: Never to buy a LED product based entirely on watts. Instead, you should focus your attention on the number of lumens you are going to need to replace the bulb.
Rule 2: You will need less LED lumens to replace Metal Halide lumens. Trust us on this one (and we explain why below).
Difference Between LED and Metal Halide Lumens
First, let’s define exactly what a lumen is. A lumen is a measure of the total quantity of visible light emitted by a light fixture. So lumens measure the amount of visible light that we can see. The way that LEDs and metal halides generate light is completely different, and because of this, LEDs can produce a much higher amount of lumens with a much lower wattage. This is the reason why we strongly suggest that you never buy new LED products based on the wattage of your metal halide lights.
So how do you know which LEDs are the best options for replacing your metal halide lights? With a photometric lighting plan. When we run a lighting-plan calculation, our software pulls all the information for a specific fixture and maps out the predicted lumens and foot-candles for a specific area. This allows you to see how your new LEDs will look in your facility, which makes them essential for replacing lighting. And, best of all, our photometric lighting calculations are free.
What You Need to Know Before Replacing Metal Halides with LEDs
1. Light Loss From Reflection
There are many things that can affect the amount of light that reaches the ground, and reflections are one of those. Lumens are measured as the light leaves the fixture, but that doesn’t mean that you’re actually getting all of that light where it’s needed. In order to measure how much light actually reaches a surface, we use foot candles.
LEDs are unique in many ways, but one of which is their directional shine. Unlike other types of bulbs, LEDs are a directional light source. This means that the light is emitted from the fixture in a specific direction. Metal Halides, however, are omnidirectional, and this means that they require some form of reflector to direct their light. If you’re wondering why this is a big deal, you’re not alone. Many people don’t realize that every time light is reflected off of a surface, lumens are lost.
If a Metal Halide bulb has 18,000 initial lumens, the loss accounted for reflected lumens drops the lumen output to around 12,600 lumens.
Yikes, that’s a lot of lost lumens, and in fact, studies have proven that you can lose up to 30% of the effective lumens in this reflective process. It’s important to be aware of this factor, because if you’re using metal halide lighting, you’re not actually able to use all of the lumens the fixture produces. So, when you buy your LED lights, make sure that you lower the lumens to avoid an overly bright workplace.
2. Quality of Lumens – CRI
Color Rendering Index, or CRI, is the best way to compare the quality of light. Light with a higher CRI rating offers better visibility and a more accurate representation of the color. The higher the quality of light, the less quantity you need. How does this affect the replacement of a 250 metal halide fixture? Well, more often than not, our customers find that 10,000 lumens of our high-quality LEDs is noticeably brighter than 18,000 lumens from other light sources, like HPS.
3. Photopic vs Scotopic Lumens
Scotopic lumens: Can be perceived by the human eye.
Photopic lumens: Can only be seen with a light meter
In many cases, lights emit rays that span across the spectrum, and some of those rays, like UV and IR, are Photopic lumens. What this means for lighting is that the majority of bulbs are using energy to produce light that we can’t even see, and therefore doesn’t do any good.
Replacing 250 Watt Metal Halide with LED
First step to start a conversion to LED?
Without a doubt, the best first step is to ask us to do a free lighting planning for you. Converting your facility (indoors or outdoors) to LED starts by deciding how many foot candles you need. Supply us with your project information, and we’ll take it from there.
And we do lighting plans for free for our commercial and industrial customers. Why? We know that a lighting plan will be the roadmap to a successful conversion to LED. And we want your project to be a success too!
About the Author
Dwayne Kula is President of LED Lighting Supply. On any given day, Dwayne is writing content for the site and helps manage the marketing initiatives that are on-going. He has a Software Engineering degree and still dabbles in writing software for the company as needed. When not working, he enjoys spending time with his family, working out, playing the occasional game of golf and exploring New England.