LED Lumens – Beyond Compare
These days, everyone is converting their lighting to LEDs. It’s not hard to understand why. LED lights offer numerous improvements over every other type of bulb on the market.
That’s just the fact. They work better with smart home systems and control and allow for color temperature control. This makes them ideal for home lighting.
They also provide significant energy-efficient benefits that save large amounts of money on energy costs. And, their better quality light improves work morale and efficiency, making them perfect for industrial and commercial applications.
But, whether you’re lighting an entire warehouse with a complicated LED system or simply looking for a bright ceiling light for your home, lighting is all about lumens. And, when business owners and other professionals are looking to upgrade their lighting to LED fixtures, some of our most asked questions are about lumens.
And, there isn’t really a straightforward answer. Why? Read on, because we’re about to go over every aspect of lumens and how to use them to ensure that your LED conversion results in a prime product.
What are Watts?
Before we get into the nitty-gritty details of lumens, we first want to quickly cover watts. There really isn’t too much to them.
A watt is defined as: a measurement of energy denoting a rate of power. When 1 amp flows through an electrical restrictor of 1 volt, the resulting energy is calculated in terms of watts.
Watts are by far the most common lighting measurement, and most people are generally familiar with what they stand for.
What are Lumens?
Now that we’ve covered watts, we can move onto the ins and outs of lumens and LED lighting. But what are lumens, exactly?
The technical definition of a lumen is: “a unit of luminous flux in the International System of Units. It is equal to the amount of light detected through a solid angle by a source of one-candela intensity.”
In laymen’s terms, lumens are a measurement of the amount of visible light a bulb emits. Now you may be thinking, “No, that’s what watts are.” This is likely because we purchase bulbs for our home based on watts instead of lumens.
The higher the watts on a lightbulb, the brighter the light. But, remember the definition of watts we gave earlier. Watts are a measurement of energy consumption. And, although once upon a time, higher energy consumption may have equaled a brighter light, that’s certainly not the case today.
But, old habits die hard. And, even though an LED light can produce a shine that’s noticeably more powerful than a traditional bulb, with less energy, the average Joe still tends to lean on watts.
Because LEDs are so much more energy-efficient than other types of lighting, we specifically use lumens to designate their light output.
More light, less energy (Watts) with LED
With low energy LED lamps, more light output can be achieved with much less power consumption. For example, a 150 Watt LED fixture will give a similar light output to a 400 Watt Metal Halide bulb.
That’s 66% less energy (including the metal halide ballast draw) for the same light output. LED lights produces very little heat when it converts electricity to light. This minimizes waste and gives us the efficient shine that we love LEDs for.
And as technology improves, this efficiency margin will become even larger. More and more lumens will be produced using fewer and fewer watts. Eventually, watts will be discarded as a measurement of brightness altogether.
Think of lumens as a way of knowing how bright a lamp is.
Lumens and Useful Lumens
With any type of bulb, some of the light emitted will be lost. This could be through reflections or via diffusions. LED bulbs significantly limit the amount of light lost because they’re made to be directional, but it really is unavoidable.
Because of this, the EU has recently introduced something called a “useful lumens” rating. This new measurement of lumens accounts for the useful light emitted by a bulb.
The “useful lumen” rating is typically lower than the total lumen output but offers a slightly more accurate prediction of how bright the light will actually be.
Lumens & Directional Light Sources
With a directional light source, you need fewer lumens.
As we mentioned, LED light is an intrinsically directional light. And, while there are led bulbs that are multi-directional, they are designed to be so and account for lost light.
In other words, the light engineer designed a fixture or bulb to place the LED chips in different positions to provide non-directional lighting and to prevent excess loss of light.
LED chips themselves provide one direction lighting. Conventional light sources, such as metal halide, high-pressure sodium, fluorescent bulbs, and incandescent bulbs are all omnidirectional light sources. Which means that they produce light in every direction. So as a general light source for home use, they work well.
However, for specialized commercial and industrial environments like warehouses, factories, and other commercial facilities, they need reflectors to gather and ‘collect’ the light in order to focus it and direct it to where it’s usable.
The problem with a reflected light source that a large margin of the light produced becomes unusable, otherwise known as lost lumens. Any internal reflection that is over one bounce effectively loses the light of one lumen.
Let’s use metal halide bulbs as an example. Like LEDs they’re popular for commercial and industrial applications. But, unlike LEDs, they are not directional. So, think of the light particles produced by a metal halide bulb.
Very few particles actually reach the floor without being reflected by at least one surface. So when a light particle is produced, it is likely to hit the fixture’s reflector, which will then try to direct it towards the floor. If it is not successful in doing this, it sends it to another section of the fixture’s reflector to repeat the process. At this point, the value of that light particle is lost.
It has been proven that you can lose up to 30% of the effective lumens in this process. But, when you use LED lighting, you receive the vast majority of their light particles, if not every single one.
Quality over Quantity
You need fewer lumens when you have better lumens.
The quality of light that any light source, even the sun, emits is measured by the Color Rendering Index, or CRI. CRI is a scale measuring the accuracy of colors produced under a specific light source. The gold medal standard is, of course, the sun which is given a score of 100. Everything else is rated on a scale between 1 and 100.
The best explanation of the quality of light is performing a simple test.
Let’s compare an LED light to High-Pressure Sodium (HPS) light. In our experience, it is not uncommon to have people tell you that 20,000 lumens of LED appears to be much brighter than 60,000 lumens of HPS. That is because the CRI value of LED is 70+, and HPS is 22.
HPS lights are infamous for coloring items that appear beneath them with a brown and yellow tinge. This is easy to anticipate if you look at the CRI value of a light before you buy it. And, with a better quality light, you need less of it. So, the higher a lights CRI ratings, the fewer lumens it needs to create the ideal shine.
When shopping for LEDs, comparing lumens alone, apples to apples, is not valid unless you take the bulbs CRI into account. Read more about CRI here.
Photopic and Scotopic Lumens
Two ways to perceive lumens.
What are Photopic Lumens?
Humans have both cones and rods in their eyes. This allows them to perceive different levels of light and color.
Photopic lumens are lumens that can only be detected by light meters and the cones within an eye. This type of light is measured by standard lumens and foot candle meters.
What are Scotopic Lumens?
Scotopic lumens is the amount of light detected by the rods and cones of the human eye. This light controls pupil size directly which affects visual acuity when doing tasks.
LED lights produce lumens that fall within the range of the spectrum that’s visible to the human eye. This means that the light created by LEDs is a usable light.
LED light does not produce IP or UV spectrums, unless they are included in the LED package of the fixture. These wavelengths are invisible to people, so they have no value to us from a vision perspective.
Scotopic lumens use a factor to adjust the photopic value of light. In lighting terminology, these are called S/P Ratios (Scotopic / Photopic Ratios). S/P rations give us a truer representation of how useful the lumens a light produces actually are.
This factor, which was developed by scientists, is an attempt to level the playing field. The factor’s used to adjust the effective value of the lumen, which may move the photopic lumen up or down.
HPS lights, oh the other hand, have a factor that reduces the effective scotopic lumen amount. LED has a factor > 1.7, which means the lumens it is producing is far more effective to us.
Less photopic LED lumens are needed to provide adequate lighting. Whereas with HPS fixtures, more lumens are needed to effectively light up an area.
To learn more about what S/P Ratios are for different light sources, click here.
Lumen Degradation of Metal Halide versus LED
It is not uncommon for HID bulbs, like Metal Halides, to lose up to 50% of their initial lumens after only 5,000 hours of life. This is concerning, but even more, concerning is that these bulbs are rated for 15,000 to 20,000 hours.
This means that the bulb is performing poorly for almost 15,000 hours of its life. And, in addition to the degradation of lumens, the quality of the light (CRI) in HID fixtures also experiences significant losses.
Many sports organizations, which often use HID fixtures are stadium and gymnasium lighting, recommend replacing Metal Halide bulbs after only 3,000 hours of use.
For a bulb that is rated for 15,000 hours of active life, the bulbs are only 20% used before they need replacing. This measurement should give you a good idea of just how quickly these bulbs degrade.
On the opposite end of the spectrum, it is not uncommon for LED light sources to have 50,000 to 100,000 hours of life where they still maintain 70% of initial lumens. This is because LED lumens degrade very slowly.
Personally, we have been very successful in replacing 400 Watt Metal Halide fixtures with our 100 Watt to 150 Watt LED Fixtures.
The feedback we get often indicates that the lights appear much brighter than the ones they are replacing, but they’re saving money on energy costs. When you take into account the quality of lumens from LEDs, their naturally higher CRI rating, and their longer usable lifespan, this is the natural conclusion.
LED Lumens – Seeing Things in a New Light
When we first came onto the commercial and industrial lighting scene in 2008, there were many many questions about LEDs, lumens, and the fixtures in general. But, the most common question by far was “Why Upgrade to LEDs?”.
Today, LEDs are extremely common, and most people are well aware of the many benefits that LED lighting has to offer. So, these questions get asked less and less.
Instead, what we see most often now, is business owners and facility managers reaching out to learn more about the process of converting their industrial and commercial lights to LED fixtures. They know that they’re more energy-efficient and that they last much longer than other bulbs.
This is because LED lights are now the standard. They’re recognized all over the globe as a money-saving, maintenance-free fixture that can adapt to virtually any application, including underwater and in extreme temperatures. People know that LEDs are better, but they want to know why.
And this can all be boiled down to LEDs and the lumens that they emit. They produce better, higher quality lumens using less energy. This helps cust on electrical costs and increases employee productivity and satisfaction.
LEDs, on average, maintain their initial lumen output for 50,000 thousand hours. This cuts down on maintenance costs because you rarely have to replace them. And, the lumens LEDs emit, have a higher CRI rating, which creates a better atmosphere in your facilities.
You could say that LED lumens are the reason for LED’s success.
How Many Lumens Do I Need?
Measure the square footage of the room you’ll be the lighting. To do this, just multiply the length of the room by the width of the room.
Decide what foot candles are appropriate for your space. The lighting requirements of a room depends on its purpose and therefore varies greatly from space to space. In an office space, for example, you’ll need more foot-candles than in a warehouse.
It’s time to figure out how many lumens you need. And, as long as you’ve followed the first two steps, there’s a pretty simple equation that will give you a good idea of what you’ll need. To determine the number of lumens your space needs, multiply the square footage by the foot-candle requirements.
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.