How to get colors with the same perceived brightness?

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.开发者_如何学编程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.

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.