Display & Surface Brightness
400 nit = 400 cd/m²
Smartphone screen (typical)
1000 nit = 1000 cd/m²
HDR TV peak brightness
100 cd/m² = 29.2 fL
Computer monitor
10,000 nit = 10,000 cd/m²
HDR reference monitor
Lighting Conditions
100,000 lux = 9,290 fc
Direct sunlight
10,000 lux = 929 fc
Overcast day
500 lux = 46.5 fc
Office lighting
0.25 lux = 250 mlux
Full moon
🔬 Photometry & Vision Science
Human Visual System & Photometry
Photometry measures light as perceived by the human eye, weighted by the luminous efficiency function V(λ). This differs from radiometry, which measures all electromagnetic radiation regardless of human perception.
Φᵥ = Km ∫ Φₑ(λ) × V(λ) dλ
Where Km = 683 lm/W is the maximum luminous efficacy at 555nm (peak human sensitivity).
Interactive Brightness Demonstration
Click buttons to see different brightness levels
Experience the logarithmic nature of human vision perception
🌈 Color Temperature & Light Quality
Light sources emit different color temperatures measured in Kelvin (K), affecting mood, circadian rhythms, and visual perception.
2700K
Warm Incandescent
Warm Incandescent
3000K
Halogen
Halogen
4000K
Fluorescent
Fluorescent
5000K
Daylight
Daylight
6500K
Cloudy Sky
Cloudy Sky
9000K
Blue Sky
Blue Sky
📚 History of Light Measurement
1860
Standard Candle First attempts at standardizing light measurement
1884
Hefner Lamp German standard for luminous intensity
1948
Modern Candela Defined based on blackbody radiation
1979
Current Definition Candela redefined using monochromatic radiation
Display Technology
HDR, OLED, brightness standards
Photography
Exposure, metering, lighting
Architecture
Daylighting, energy efficiency
Research
Vision science, circadian studies
Automotive
Headlights, HUD, safety
Agriculture
LED grow lights, plant biology