It is crucial to consider a light bulb's brightness when planning a lighting project. Most people are already familiar with watts, which measure the power of light bulbs, but “lux” and “lumens” have become two of the most commonly utilized units of measurement across the lighting industry.
This article will break down the differences between lux and lumens and hopefully help you feel more informed when completing your next lighting project.
Defining Lux and Lumens
Lux and lumens are both metrics related to light brightness with only slightly different meanings.
To put it simply, Lux measures how much light falls on a surface and lumens (or luminous flux) measure how much light is emitted by the light source.
Lux is a measurement of illuminance, meaning the amount of light that strikes a surface that is visible to the human eye. This is not to be confused with the amount of light that a light source emits (lumens). A light source may emit "X" photons, but some of those photons may never reach the surface of the object you are viewing. Additionally, some of these photons may be absorbed by the surface they are illuminating, making them invisible to the eye.
Lux varies depending on the light source, the objects distance from the light source, the surface brightness, the size of the light beam, and other factors like sunlight. For example, if you have the same light bulb inside a flashlight with a highly concentrated beam compared to a standard table lamp, your units of lux will vary substantially because of their different outputs.
The most common unit of measurement utilized by lighting producers today is lumen. It is backed by the Federal Trade Commission, which requires all manufacturers to include lumen information on their packaging, so you likely have seen this term when picking up a pack of light bulbs from your local store.
Lumens are a measurement of luminous flux, which refers to how much light a source can emit. This metric shows the total amount of light that the light source has emitted regardless of direction or external sources. Efficiency is a key factor in measuring lumens since they describe how effectively the light source transforms power into light.
Measuring Lux and Lumens
Efficiency, productivity, and safety can all be significantly improved by providing the appropriate level of light fo and lumen metrics to optimize the functionality of your space.
Lux is particularly important for knowing how bright a particular surface appears. This metric is important to consider when trying to light art on a studio wall, when working with a photography subject, or when lighting a desk frequently used for reading or writing.
Since lux is the measurement of how much light appears on a surface, the amount of lux will vary with sunlight or the use of other light bulbs, so keep this in mind when calculating units of lux needed to light your space.
Lighting industry professionals have created a general rule for minimum lux levels suggested for maximum comfort and efficiency in common spaces. If you’re ever unsure what lux levels you need in your space, this is a good rule of thumb to follow:
- 100-150 lux for restrooms, elevators, hallways
- 250 lux for conference rooms, libraries, and classrooms
- 500 lux for retail stores and offices
- 750 lux for factories and indoor sports venues
- 1000 lux for operating rooms
Lumens (denoted by lm) measure how efficiently a light source converts energy to light. The higher the lumen level, the brighter light will appear to the human eye. Since this measurement is surpassing watts in the lighting industry as LEDs become more prominent, it is important to familiarize yourself with how lumens measure up against watts. There are approximately 12.5 lumens per watt and the average 60-watt light bulb has 750 lumens. Nowadays, lumen ratings are prominently stated on the packaging and lamp base of most LED bulbs, so even a lighting novice can make an informed decision when purchasing your standard bulb.
If necessary, we recommend referring to conversion charts, which are readily available on the internet and often displayed on light bulb packaging.
When choosing a light source with an appropriate lumen level for your space, there is no definitive suggestion because many factors influence lumen levels, including square footage, lamp types, ceiling height, etc. but as a general rule, you want your lumen level to be appropriate to your room's functions and to have that lumen level per square meter. Here is a reference of common lumen/sq M applications:
- 300-400 lm/sq M for a home kitchen
- 700-800 lm/sq M for a restaurant kitchen
- 300-400 lm/sq M for bedrooms, livings rooms, reading rooms
- 700-800 lm/sq M for any high task rooms such as factories or retail spaces
Our lighting experts at Shine Retrofits can help talk you through our wide range of light bulbs or advise you on the best lumen and lux ratios for your project. Give us a call at 1-877-643-4534 anytime Monday through Friday, from 6 am to 6 pm, Mountain Standard Time. We can’t wait to hear from you and help you get your project off the ground!