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How to upgrade conventional light fixtures to LED?

It’s not easy to determine the ideal lumen output of an LED fixture to replace traditional light sources. Numerous factors need to be taken into account, such as initial lumen production, optical efficiency, and lumen maintenance.

Initial lumens

The lighting levels when constructing a place with conventional light sources are based on design or mean lumens, not initial lumens. This information is typically included in the manufacturer’s spec sheet for the lamp and/or fixture. The initial lumen output of a 400W metal halide lamp is 36,000, while the mean lumen output is 24,000 on average. Based on this, you could assume that switching a 400W MH lamp out for a 24,000 lumen LED light is the solution, but perhaps not… simply wait.


For conventional light sources, design or mean lumens are commonly assessed at 40% of lamp life. For instance, 400W MH produces 24,000 mean lumens and 36,000 initial lumens. With a 15,000-hour rated life, the lumen output is about 24,000 lumens at 6,000 hours and 18,000 lumens at 15,000 hours.

A 400W Metal Halide lamp with a 15,000-hour rated life will produce 24,000 lumens after just one year of continuous use, which is typical in industrial lighting. What occurs between years two and three, though? By year two’s end, there are just 17,000 lumens of light left. Your current view is a 17,000 lumen LED. Perhaps… but take into account how often end consumers replace their bulbs. Most people put off changing their lamps until they burn out or become excessively dim.

When lighting work spaces, there are other factors besides lumen output to take into account. When choosing a replacement, it is important to consider the end-needs, user’s the design and use of the space, and the IES recommended light levels.

Optical efficiency

Traditional lighting fixtures consist of a reflector or refractor to focus the light where it is needed and tubular, elliptical, or bulb-shaped lights that emit light in all directions. Significant light losses result from this, which vary depending on the reflectors’ design, caliber, and cleanliness. Optical efficiency is the measure of how many lumens the light source produces in relation to how much light the fixture really emits.

So what is a 400W MH fixture’s usual optical efficiency? The typical falls between 65% and 80%. When we apply an optical efficiency factor of 70% to a 400W MH with a mean lumen output of 24,000 lumens, we obtain 16,800 lumens.


The difference between the amount of light coming from the fixture and the amount of light generated. The typical lamps’ design sends light in all directions, necessitating the use of a reflector to focus it where it is needed. There may be considerable light losses depending on the reflector type. Metal halide high bays with an average 400W output have an optical efficiency of 70%. For the majority of high bay applications, fixtures use lenses rather than reflectors and LEDs have a more directed light, resulting in optical efficiency in the 90% range.

LED life vs. measured life

Unlike traditional light sources, LED life is not quantified in the same way. We predict the point at which the initial lumen output will fall by 30% for LEDs. This type of fixture is referred known as L70 since it produces 70% of the initial lumen output. Anything below L70 is considered unacceptable for productivity and safety at this point, and the IES (Illuminating Engineering Society) recommends replacing the fixture. 

An algorithm based on initial data and extrapolations determines L70. The estimated L70 hours vary significantly depending on the fixture’s design and the operating environment; for example, they are not equivalent in an office at 25°C (77°F) and a steel plant at 55°C (131F). The range is between 50,000 and more than 300,000 hours. If you choose a fixture with a lower projected L70, it would likely require a fixture with a considerably greater starting lumen output, such as 24,000 lumens, to make up for the sharp decline. You might be able to choose a 17,000-lumen type that is more energy-efficient and less expensive if the fixture you use is a high-quality LED with a longer L70 at higher ambient temperatures.

So how do we make a choice? The ambient temperature in the application, lumen maintenance, efficiency, client needs, and IES-recommended light levels must all be taken into account.

Since every fixture has a different set of properties and LED quality varies widely, there is no easy formula. We should also consider when we require that particular light level. The delivered lumen range for 400W MH lights is from 25,000 to 13,000 lumens at end of life (15,000 to 20,000 hours depending on the brand of the included lamp). Due to their inadequate thermal design, lower-quality LED lighting frequently experience a significant reduction in light output as a function of ambient temperature. After only a few years of use, it is typical to observe them lose 50% of their initial lumen output at moderate temperatures. 

So the question is: for how long do you require a particular light level? Day 1? Year 1? or 10th grade? Long L70 LED fixtures with good design should have years of low maintenance and consistent light output.


Traditional source life is calculated based on the number of hours it takes for 50% of the lamps to burn out, thus if that number is 20,000 hours, that is how long your source will last. L70, the number of hours it takes for a 30% reduction in lumen output, is used to test LED. Ballast and driver life are not taken into account by either of these systems; those topics require their own treatment.

Don’t make any assumptions when it’s time to replace your old light fixtures. You must conduct a study on the lumen output, efficiency, and L70 life of the particular fixtures you are thinking about. Examine or request performance information for your facility’s ambient temperature. Never compare apples to apples, and stay away from deceptive marketing.

But are all lighting spec sheets reliable?

Specific information and specifics regarding a fixture are provided in spec sheets. But can you believe these spec sheets? Many spec sheets are intended to deceive. Verify that you are not being duped.

Preventing information on LED high bay specification sheets from deceiving you.

How do you know that the information you are receiving from your lighting suppliers is accurate if your line of work involves advising or specifying lights for your clients? Everyone is attempting to persuade you to buy their product on on some presumption of efficacy, rated life, or unique feature. How can you be sure you are obtaining accurate data?

When it comes to the data sheets provided by the majority of lighting manufacturers, the adage “caveat emptor”—let the buyer beware—certainly applies. The majority of them provide fundamental details on topics like form factors, lumen packages, energy consumption, choices and accessories, and the L70 life of the luminaire.

They all seem wonderful at first glance, boasting amazing LPW calculations and L70s, and you joyfully specify the product only to be let down when it doesn’t live up to your expectations. Keep in mind that the client will eventually accuse someone. Would you rather that they point at you?

When it comes to the LED high bay industry, the following practice looks to be a liar’s haven.

L70’s story

When examining L70 data on spec sheets, exercise caution. The majority of producers only display data at the TM21 25°C level. That’s excellent if your high bay is being installed in a climate-controlled space. What would happen if you installed the luminaire in a location where the ceiling was frequently 130° or 140°F? In those conditions, wouldn’t you want to be familiar with the L70?

In order to avoid coming off as unduly cynical, the majority of manufacturers fail to mention how poorly the fixture performs at its ambient temperature on its spec sheets since it actually performs horribly. You can ask those businesses for the info. You might be fortunate and succeed in getting it. I would advise you to only do business with manufacturers who are willing to freely share that information or who have already made it available on their specification sheet.

I would like to know how well the fixture is expected to function at its ambient operating temperature because I specify luminaires. Value pricing, which occasionally comes with less expensive high bays, can end up costing your client more in the long run due to maintenance and replacement costs.

How to choose the right lumen output when upgrading conventional light fixtures to LED

Buyer beware of the overstating performance in spec sheet!

Even while it could appear to be the greatest fixture at first glance, what happens when you look closely? Are all of the details appropriate for your application’s requirements? You must examine that fixture in the required configuration because several factors can alter its efficacy.

Efficacy is defined as Delivered Lumens/Energy(Watts)=LPW. Although this is the traditional formula, is it accurate?

What about CRIs of 70, 80, and 90? These have an effect and may cause the LPW to be derrated. Likewise, how about CCT? Are 4000K and 5000K more effective than 3500K? It might not be, depending on the manufacturer of the chip. Has the optic any effect? Do narrower lenses provide more lumens than wider ones? Does a clean lens perform better than one that is frosted? Exists a lens-free option? The genuine LPW of the luminaire is impacted by all of these variables.

A producer will frequently state, “We have 200LPW,” or something like. They might, but is it set up the way you would want?

The manufacturer’s lineup often includes the Spec Sheet Star as its most effective fixture.

It probably starts off as the top-performing fixture, but upon closer inspection, it turns out that the fixture is 70 CRI, 5000K, without a lens, and that it performs best at 25 °C ambient. If that is your operating environment, feel free to specify; it should work just fine.

But what if you want 80CRI, at 4000K, with a frosted lens to cut glare, and you’re installing the device in a setting where the ceiling’s maximum ambient temperature is 55°C?

In this situation, you must determine real performance using the manufacturer-provided derating factors. These elements should be listed on the spec sheet by the majority of respectable manufacturers, but you must look for them.

The example below shows how a well-known manufacturer claimed 167LPW for their base fixture, but after accounting for all derating factors, the actual LPW was only 138LPW. Not terrible, but not what was promised on the base fixture, which is frequently all that is read. To be fair to this company, all the necessary details could be found on the spec sheet if you just looked. It’s probably advisable to move on from a manufacturer if they can’t give you that fundamental information. Remember that in the end, it’s all about your reputation.

Actual values against advertised values

Here is an illustration of how advertised lumen and efficacy and actual lumen and efficacy in an application differ. The wattage will probably be the only constant in this design; it shouldn’t fluctuate.

Advertised Information:
Initial Lumens48,000
Initial Watts284
Efficacy LPW167

In this case, the manufacturer’s initial claim of 167LPW was changed to 138LPW once the proper lumen adjustment multipliers were used. The fact that I was expecting a nominally 48,000-lumen fixture but instead received a 40,000-lumen fixture—17% less performance—is of greater concern to me. That is a sizable difference that might affect how well the lighting system works after it is built.

So you should thoroughly read the specification sheet and pay attention to all the tables and references. Even though the manufacturer might not be intentionally misrepresenting you, they could not be making it as simple for you to find the solutions. Make sure you are aware of the performance you can anticipate from the LED luminaire in the actual setting.

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