Illuminance - Recommended Light Levels
Recommended light levels - illuminance - for some common types of working activities
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Light Level or Illuminance, is the amount of light measured in a plane. The work plane is where the most important tasks in the room or space are performed.
Measuring Units Light Level - Illuminance
Illumenance is measured in foot candles (ftcd, fc) (or lux in the metric SI system). A foot candle is actually one lumen of light density per square foot, one lux is one lumen per square meter.
- lux = fc 10.752
- fc = lux / 10.752
Common Light Levels Outdoor
Common light levels outdoor at day and night can be found in the table below:
| Condition | Illumination | |
| (ftcd) | (lux) | |
| Sunlight | 10,000 | 107,527 |
| Full Daylight | 1,000 | 10,752.7 |
| Overcast Day | 100 | 1,075.3 |
| Very Dark Day | 10 | 107.53 |
| Twilight | 1 | 10.75 |
| Deep Twilight | .1 | 1.08 |
| Full Moon | .01 | .108 |
| Quarter Moon | .001 | .0108 |
| Starlight | .0001 | .0011 |
| Overcast Night | .00001 | .0001 |
Common and Recommended Light Levels Indoor
The outdoor light level is approximately 10,000 lux on a clear day. In the building, in the area closest to windows, the light level may be reduced to approximately 1,000 lux. In the middle area its may be as low as 25 - 50 lux. Additional lighting equipment is often necessary to compensate the low levels.
Earlier it was common with light levels in the range 100 - 300 lux for normal activities. Today the light level is more common in the range 500 - 1000 lux - depending on activity. For precision and detailed works, the light level may even approach 1500 - 2000 lux.
The table below is a guidance for recommended light level in different work spaces:
| Activity | Illumination (lux, lumen/m2) |
| Warehouses, Homes, Theaters, Archives | 150 |
| Easy Office Work, Classes | 250 |
| Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories | 500 |
| Supermarkets, Mechanical Workshops, Office Landscapes | 750 |
| Normal Drawing Work, Detailed Mechanical Workshops, Operation Theatres | 1,000 |
| Detailed Drawing Work, Very Detailed Mechanical Works | 1,500 - 2,000 |
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