Luminance is a measure of the perceived brightness of light reaching the human eye, considering both the amount of light emitted, transmitted, or reflected from a surface and the human eye’s sensitivity to different wavelengths of light. In simpler terms, luminance quantifies how bright a surface appears to the human eye under given conditions.
- Luminance focuses on luminous intensity as experienced by an observer. While luminous intensity refers to the amount of light emitted in a specific direction by a source, luminance measures how bright a surface appears based on both the light it reflects or emits and the observer’s perspective.
- For example, imagine a lamp shining in a dark room. While the lamp emits a certain amount of total light (luminous flux), the actual brightness (luminance) of a wall the light falls on depends on several factors:
- Reflectivity: The wall reflects only a portion of the light that hits it. The amount of light reflected affects the overall luminance the human eye perceives.
- Spectral Sensitivity: Human eyes are more sensitive to green light than to blue or red light. Therefore, even if two surfaces receive the same light, a green surface will appear brighter than a blue one because of the eye’s higher sensitivity to green wavelengths.
- Measuring luminance helps us understand real-world scenarios:
- Moonlight: While not very luminous (doesn’t emit much light), moonlight creates a certain luminance on sand in a desert, allowing us to see our surroundings.
- Road safety: Streetlights need specific luminance levels to ensure safe visibility for drivers, considering both the total light emitted and road reflectivity.
- Book reading: The luminance of a book under a lamp determines how comfortable and clear the text appears to your eyes.