American Green Lights
Lumens, Lux, and Foot-Candles
Light output vs. Light intensity
Lumens is a measurement of light output. Lux and Foot-candles are a measurement of light intensity. Lumens, Lux, and Foot candles are closely related, but often confused as to the meaning and how to use the information to make lighting decisions.
Lumens are generally indicated on specifications of lighting fixtures or light sources such as bulbs, tubes, strips, or other products. Lumens are a measurement of the total light output of a device at the light source.
Understanding LUX and Foot-Candles
Lux (lx) and Foot-Candles (fc) are measurements of light intensity or light density. Light intensity is measured at a specific location, such as at the desktop, or workbench, or the work surface of tools.
Light Intensity vs. Fixture Height
In the three light intensity map images to the right, you will see the same floor plan with fixture height at 8ft, 10 ft, and /12 ft heights. All three have the same nine units of 48 Watt shop light fixtures in the same location on the ceiling.
The numbers in the light intensity map indicate foot-candle
intensity at the surface measured (work surface height
where tools and workbenches exist and at the floor height
where there is no worksurface).
Please note the following differences in intensity levels:
---8ft = 85fc, 85fc, 85fc
---10ft= 80fc, 75fc, 79fc
--12ft= 69fc, 66fc, 70fc
---8ft = 74fc, 79fc
---10ft= 63fc, 70fc
---12ft= 54fc, 61fc
Miter Station (Left Wall)
---8ft = 65fc, 75fc, 78fc, 66fc
---10ft= 51fc, 61fc ,60fc, 54fc
---12ft= 42fc, 50fc, 55fc, 47fc
At Floor Upper Right Corner
---8ft = 40fc
The color legend indicates the foot-candle intensity
that corresponds each color on the light intensity
map. Red=100 foot-candles, black= 0 foot candles.