Lux is the globally standardized SI unit of illumination. It provides a uniform standard by which the amount of visible light present in a given space can be described. A lux rating is used to describe the perceived illumination of a known space, such as a room or a stage.
The lumen is the globally standardized SI unit of "luminous flux"--meaning that it measures just how much visible light is produced by an object such as, for example, a light bulb.
With clarity on the difference lumens and lux, conversion between the two is simple.
Things You'll Need
- Pen and paper
- Calculator (optional)
- Photometer (optional)
The Difference Between Lumens and Lux
Lux is a measure of how many lumens are present in a given area. It's essentially a measure of "photon density" or "light concentration." A "denser" cloud of photons means there are more lumens present in a space--producing more brightness and higher lux. A "lighter" cloud of photons means fewer lumens--leading to dimmer conditions and lower lux.
To illustrate the difference between lumens and lux: While the sun always produces the same number of lumens, on cloudy days there are fewer lux outdoors. At night, only the lumens provided by the moon and stars reach the ground, leading to extremely low lux under a night sky.
To achieve a desired lux level in a given space it may be necessary to use many light bulbs, each producing a given number of lumens.
Do the Conversion
Measure the dimensions of the space that you wish to illuminate, and write down how many square meters of surface area it has.
Know what lux level you wish to achieve in that space. Consult lighting manuals or subject specialists to narrow down a good lux level for your application. For example, 500 lux is a standard moderate illumination level for an indoor room.
The fundamental ratio of conversion from desired lux level to required lumens is:
1 lux = 1 lumen per square meter. This is equivalent to: 1 lux = 0.0929 lumens per square foot.
Tips & Warnings
- To usefully convert from desired lux to required lumens, you'll need to know the radiance properties of your light (i.e., lumen) sources, their orientation in the room and other factors such as whether they radiate omnidirectionally (such as an open candle flame or unshielded light bulb) or have a narrower, directed beam (such as a flashlight or spotlight).
- Photo Credit BananaStock/BananaStock/Getty Images
Foot-Candles Vs. Lumens
A "foot-candle" is a unit of measure for quantifying the intensity of light falling on an object. A "lumen" is a unit...
How to Convert Footcandles to Watts per Square Meter
Light intensity is important to photographers, gardeners and astronomers alike, but there are different ways of measuring it. Photographers are primarily interested...
How to Calculate Illuminance
Illuminance is the quantity of light incident on a surface per unit of area. In the U.S., lumens per square foot is...
How Do I Measure Lux Lighting?
Where lumens measure the amount of light a light source emits, lux tells how much that light source illuminates an object or...
How to Convert NITS to LUX
Lux and nits are both measurements of illuminance or illumination. In other words, they are measures of the intensity of light. Analogous...
How to Convert Lux to Milliwatts
Lux measures the intensity of light that reaches the eye. Milliwatts, however, measures the light's total rate of energy transfer in joules...
How to Calculate Lux
Lux, the Latin word for "light," is the SI unit of illumination. One lux is equal to 1 lumen per square meter....