Daylight

Daylight Definition and Variability

• Daylight is present when the Sun is above the local horizon.
• Outdoor illuminance varies from 120,000 lux for direct sunlight at noon to less than 5 lux for thick storm clouds.
• Illuminance can drop to 1 lux during a solar eclipse.
• Daylight intensity can be affected by atmospheric particulates, dust, smoke, and volcanic ash.

Daylight Intensity Measurements

• Brightest sunlight measures around 120,000 lux.
• Bright sunlight reaches about 111,000 lux.
• A full Moon on a clear night sky registers 0.25 lux.
• Starlight on a moonless night sky can be as low as 0.002 lux.
• Venus at its brightest in a clear night sky measures 0.00014 lux.

Related Concepts

• Artificial sky
• Color temperature
• Daylight harvesting
• Daylight saving time
• Daylighting

References

• Cox, Clifford. Dust Bowl.
• Volcanic Ash Impacts & Mitigation. USGS.
• Air mass (solar energy). Wikipedia.
• Interference of moonlight with photoperiodic measurement by plants.
• Radiometry and photometry in astronomy FAQ.

Daylight Data Sources