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Lux vs Lumens: What’s the Difference?

Measurements of light that appear on the boxes of bulbs in the store can be confusing. From wattage to lumens, and lux, having a basic understanding of the differences among them can go a long way towards finding adequate, inviting lighting for any room or outdoor space.

Here, we’ll illuminate the differences between lux vs lumens, so you can choose the perfect lighting solution.

Lux

The total amount of light that the human eye perceives on a surface is known as illuminance, which measures in terms of ‘lux’ (1). Depending on the distance from a light source, lux allows you to get an idea of how bright an illuminated surface will appear. 

Lumens

As the most common unit for lighting equipment you’ll likely find, lumens relate to luminous flux. This unit of light current tells you how much a source of light will emit in total. By definition:

The luminous flux dF of a source of luminous intensity I (cd) in an element of solid angle dR is given by dF = IdR

In simpler terms, lumens are the total amount of visible light that you can expect to see.

A 200 Lumen Pathway Light

Comparing the Details: Lumens vs Lux

Lux is a measurement of the intensity that a light source gives off, and lumens measure the same source’s total output. Because of this, they have a direct yet somewhat complicated relationship. Here we’ll take a closer look at lux vs lumens, starting with examining “luminous flex” and “illuminance.”

Luminous Flux and Illuminance

The power of light that we perceive, or luminous flux, takes each wavelength of light, weighing it with a luminosity function. With human eyes’ sensitivity in mind, this sum excludes ultraviolet and infrared light, giving the resulting measurement in lumens. Lux measures illuminance, which is the total luminous flux we see reflected upon a surface. 

Lumen and lux measurements have the same source but look at different variables within this source.

Photometric vs. Radiometric Units

There are two types of measurement units when it comes to the light spectrum (3). Radiometric and photometric units help us to understand both the physical and perceived energies of light.

Photometric light measurements consider our eye sensitivity and only the visible wavelengths. On the other hand, radiometric units measure all light’s power output and not just what we can see.

Lux and lumens are both photometric units, and an example of a radiometric unit is wattage.

When to Use Which Measurement

Looking for the right light amount can be overwhelming, especially with all the measurements and confusing terminology. That said, making a choice based on lux or lumens can make a huge difference.

The Institute of Physics states:

The luminous intensity of a source depends on the power emitted in a particular direction, as we’re usually interested in lighting something, not just lighting.

That said, to determine if a light bulb will have ‘enough’ light projected to a particular area, you will want to pay attention to the lux reading. When it comes to power output and how much light will emit from the source, lumens are where to look.

This can get confusing, so to help this all sink in, you can check out this great video comparing lumens vs lux from HEINE for a visual:

Lux to Lumens Calculation

Since lux is the measurement of luminous flux, there is an equation to make this conversion and show its exact difference. At its most straightforward, one lux equals one lumen per square foot.

The Omni Calculator says:

“The measure of illuminance (on the receiver surface) is the total emitted light in lumens divided by area: lux = lumens / area” (5)

This equation tells us that to measure lumens, you need lux and that the two must go hand in hand in determining brightness and the total amount of light output. So if you ask the question like in our recent article, “How many lumens do I need for outdoor lighting?” lux will be contained in your answer.

The Bottom Line

Whether you’re looking for a light bulb, flood light, projector, or any other lighting product, both lux and lumens measurements can help you determine your ideal light output and the total amount of visible light. The subtle difference of light emitted versus the light that we see makes a difference in some situations more than others, and it is up to you to determine what is most important in your case.

FAQs

Anything over 1,100 lux may be too bright for proper lighting in your home (6).

Sometimes, large amounts of lux can cause damage to specific items. For museums, this can be a big deal, and it is essential to limit exposure to artifacts and artwork. Plus, room to room the amount of lux you’ll need will vary.

No, lux is not necessarily “better” than lumens.

Lux can help you determine how bright a hotspot will be at the end of your light. This could be helpful with a picking a solar spotlight where your goal is to illuminate an end-point. Lumens can help you get an idea of how bright a light will be in total. This could help with picking a solar flag pole light where the idea is to illuminate the whole flag.

The ideal lumen measurement for a room will depend on a combination of personal preference, and the room itself.

For bedrooms or sitting rooms, 10 to 20 lumens per square foot is a good amount. Kitchens and bathrooms need brighter lighting, so around 70 to 80 lumens per square foot works well.

For more lighting tips to improve your home’s energy-efficiency and overall energy usage, head on over to our Homepage.

  1. Lux. Retrieved from: https://www.circadiansleepdisorders.org/info/lux.php
  2. The Lumen and the Lux. Retrieved from: https://www.conservationphysics.org/lightcd/lumen.html
  3. Radiometry and Photometry FAQ. Retrieved from: https://wp.optics.arizona.edu/jpalmer/radiometry/radiometry-and-photometry-faq/
  4. Measures of Brightness. Retrieved from: https://spark.iop.org/measures-brightness#gref
  5. Lux to lumen conversion. Retrieved from: https://www.omnicalculator.com/physics/lumen#lux-to-lumen-conversion
  6. Ergonomic Lighting Levels by Room for Residential Spaces. Retrieved from: https://www.thoughtco.com/lighting-levels-by-room-1206643
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