How to Use the Relative Luminance & Perceived Brightness Meter
-
1
Enter any HEX or RGB color.
-
2
The tool computes: Relative Luminance ($Y$ between 0.000 for pure black and 1.000 for pure white) using the official WCAG 2.1 formula.
-
3
View HSP Perceived Brightness (which accounts for the human eye's heightened sensitivity to green light).
-
4
The meter automatically declares whether Black (`#000000`) or White (`#ffffff`) text provides higher contrast readability.
Practical Example & Use Case
Common Real-World Scenario
Testing `#ffcc00` (Yellow) reveals a high relative luminance of 0.648, indicating that black text is mandatory for readable contrast.
Technical Notes & Limitations
Browser Engine Architecture
Calculates mathematically exact CIE 1931 linear RGB luminance: $Y = 0.2126R_{lin} + 0.7152G_{lin} + 0.0722B_{lin}$.
Frequently Asked Questions
Why is green weighted so heavily in relative luminance?
The human eye's retina has far more green-sensitive cone photoreceptors than red or blue, making green appear naturally much brighter.