Signed in as:
filler@godaddy.com
Light Intensity: Lumens, Lux, 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.
Understanding Lumens
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.
- LUX is a measurement of Lumens per square meter.
- Foot-candles is the imperial equivalent and is a measurement of lumens per square foot.
- One LUX (lumen per square meter) is equal to 10.7639 foot-candles (lumens per square foot)
- The further away from the light source, the less intensity. The dropoff in intensity is exponential, not linear.
How bright should your workspace be?
Examples of recommended light levels are:
- School classroom= 30-50fc
- Residential kitchen= 70-85 fc
- Woodworking Shop= 60-100fc
- Commercial kitchen= 100fc
- General factory= 40-70fc
- Automotive service bay= 50-75fc
- Commercial warehouse= 15-20 fc
- Typical residential garage= 5-20fc
- Workbench at opening of open garage door in the shadow of the garage, but bright sunshine outside= 150-250fc
- Workbench outdoors on overcast day where shadow is not visible, but almost visible= 850-1200fc
- Workbench in direct sunlight= 10,000 fc
- Competition basketball court= 80fc (non-televised) to 125fc (national championship televised)
- Tennis court 75 (non-televised) to 125fc (national championship televised)
Fixture height affects light intensity and spacing
Lumens are spread over a larger area as the light source gets further away, exponentially reducing intensity.
In this 20'x20' garage woodshop example, there are nine fixtures of 48W each positioned as above.
This legend indicates which color corresponds with specific light intensity.
The numbers below on the heat map are in foot candles.
The three images below are with fixture height of 8ft, 10ft, and 12ft and show the affect of height on light intensity.
Please note the following differences in intensity levels:
Table Saw:
---8ft = 85fc, 85fc, 85fc
---10ft= 80fc, 75fc, 79fc
--12ft= 69fc, 66fc, 70fc
Jointer:
---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
---10ft= 36fc
---12ft= 33fc
There is overlap of light from one fixture to the next and therefore the center will always be brighter than the walls and corners.
This can be mitigated by increasing the wattage of the fixtures in the corners of the room and along the walls.