Luminance is a measure of the perceived brightness of light reaching the human eye, considering both the amount of light emitted or reflected from the surface and the sensitivity of the human eye to different colours. So luminance is a scientific measure of how bright a surface appears to the human eye.

  • luminance focuses on the brightness experience. Imagine a lamp shining in a dark room. While the lamp emits a certain amount of light (luminosity), the actual brightness on your wall (luminance) depends on several factors:
  • The wall reflects only a portion of the emitted light, impacting the overall brightness you perceive.
  • Our eyes are more sensitive to green light than blue light. So, even if two surfaces receive the same amount of light, a green one will appear brighter due to this sensitivity difference.
  • Measuring luminance helps us understand real-world scenarios:
    • Moonlight: While not very luminous, moonlight creates a certain luminance on the desert sand, allowing us to see our surroundings.
    • Road safety: Streetlights need specific luminance levels to ensure safe visibility for drivers, considering both emitted light and road reflectivity.
    • Book reading: The luminance of your book under a lamp determines how comfortable and clear the text appears for your eyes.

Remember, luminance is a measurable quantity, meaning we can use instruments to analyze the brightness of various objects and light sources.

  • Luminosity signifies the total amount of visible light emitted by a source, measured in watts or lumens. It’s like the raw power output of light, similar to an engine’s horsepower.
  • Luminance, on the other hand, tells us about the perceived brightness of that light when it reaches our eyes. It considers multiple factors:
    • Luminosity of the source
    • Reflection of the surface receiving the light
    • Human eye’s sensitivity to different wavelengths
  • Think of it this way: a powerful light source (high luminosity) might shine on a dark surface (low reflection), resulting in a lower perceived brightness (lower luminance).
  • Conversely, a weaker light source shining on a highly reflective surface could still lead to a higher perceived brightness due to the reflection boosting the received light.