why green light is usually looks brighter than red or blue light in human sight

The perception of brightness in relation to light colors like green, red, and blue is influenced by various factors related to human vision. Here are a few reasons why green light often appears brighter than red or blue: 1. **Sensitivity of the Eye**: The human eye has different types of photoreceptor cells called cones that are sensitive to specific ranges of wavelengths. There are three types of cones: S (blue), M (green), and L (red) cones. The M-cones are most responsive to green light. 2. **Luminance**: Green light has higher luminance than red or blue light at the same intensity. This means greater energy per photon results in less divergent spreading, which makes green light appear brighter. 3. **Luminous Efficiency**: The eye's sensitivity, or the luminous efficiency function, peaks for green-yellow wavelengths around 555 nm. This region roughly corresponds to the sensitivity of the M-cones. Red and blue lights have their peak sensitivities lower than this value. 4. **Pupil Adjustment**: The pupil’s automatic adjustment to various light intensities also helps maintain an optimal amount of light entering the eye; however, it isn’t specific to color but rather overall brightness. 5. **Chromatic Aberrations**: Due to the way light enters the eye and gets processed by the rods and cones, certain colors (including green) might seem somewhat more intense because similar wavelength light is closer to the peak response of the eye. 6. **Adaptation and Color Constancy**: How our brain perceives and interprets color (color constancy) also plays a role in whether certain colors appear brighter. We often judge perceived brightness in context, so what may be determined as "bright" can vary based on surroundings and color contrasts. It is important to note that these factors can vary from person to person due to individual differences in vision. While green usually appears brighter, the perception could differ based on variations in natural color vision (like color blindness) or under specific lighting conditions.