How to get colors with the same perceived brightness?

Question

Is there a tool / program / color system that enables you to get colors of the same luminance (perceived brightness)?

Say I pick a color (determine RGB values) and the program gives me all the colors around the color wheel with the same luminance but different hues?

I haven't seen such tool yet, all I came across were three different algorithms for color luminance:

(0.2126*R) + (0.7152*G) + (0.0722*B)
(0.299*R + 0.587*G + 0.114*B)
sqrt( 0.241*R^2 + 0.691*G^2 + 0.068*B^2 )

Just to be clear, I'm talking about color luminance / perceived brightness or whatever you want to call it - the attribute that encounters that we perceive red hue brighter than blue for example. (So 255,0,0 has higher luminance value than 0,0,255.)

P.S.: Does anyone know which algorithm is used to determine color luminence on this website: http://www.workwithcolor.com/hsl-color-picker-01.htm It looks like they used none of the posted algorithms.

Answer 1

In the HSL color picker you linked to, it looks like they are using the 3rd Lightness equation given here, and then making it a percentage. So the equation is:

L = (100 * 0.5 * (max(r,g,b) + min(r,g,b))) / 255

Edit: Actually, I just realized that they have an L value and a Lum value shown on that color picker. The equation above applies to the L value, but I don't know how they are arriving at the Lum value. It doesn't seem to follow any of the standard equations.