why the color 00ff00 is usually looks much brighter than the color 0000ff

The perceived brightness or vividness of a color can relate to several factors, including luminance and saturation. Let's examine why `00ff00` (bright green) may appear brighter than `0000ff` (blue): 1. **Luminance:** Luminance, which refers to the perceived brightness of colors, is influenced significantly by the presence of green and red, which are the primary wavelengths in the color spectrum that human eyes are most sensitive to. `00ff00` has full intensity green and no blue or red component, but since human eyes are more sensitive to green, this hue appears brighter. 2. **Color Saturation:** While both `00ff00` and `0000ff` are highly saturated (fully saturated in their respective primary colors), brighter colors have higher reflectivity or transmittance, meaning they scatter light better. Green light is closer to visible light peak sensitivity than blue light. 3. **Addition vs. Subtraction:** The color we perceive from a light source is typically additive mixing (for example, on a TV) where all primary lights (including green) combine to form white. In contrast, pigment-based colors (like those in printed media) mix subtractively and are based on absorption of different light wavelengths. When using subtractive color, you might get a less "bright" or more muted result for green compared to an additive representation like on a screen, although both should theoretically seem bright due to high chroma. However, human perception also affects our interpretation. 4. **Contrast and Context:** When looking at `00ff00` and `0000ff` on a neutral or white background, the green pops out more because it stands out more against the typical environment colors we see every day. 5. **Hue-Dependent Brightness Perception:** Studies have shown that humans perceive blue as darker than green even when two have the same intensity due to varying receptor responses for different colors. These factors contribute to why `00ff00` (pure green) often looks brighter than `0000ff` (pure blue), though both colors are fully saturated.