HSV and HSL are cylindrical transformations of the RGB color cube model.
HSV (hue, saturation and value) and HSL (hue, saturation and lightness) were first described by Smith, Joblove and Greenberg in two articles in an ACM SIGGRAPH Computer Graphics issue from 1978.
Smith gave algorithms for conversion between HSV and RGB and between HSL and RGB in his article. Smith gave a formulation of HSV based on a hexcone representation and HSL based on a triangle representation.
Joblove and Greenberg gave an alternative formulation of the HSV color space based on a cylindrical representation.
Metrick and the graphic standards planning committee later gave a double-hexcone representation for HSL and improved the algorithm for conversion between HSL and RGB with one that does not require sqrt(), cos(), and arctan(). Fishkin finally improved the performance for conversion from HSL to RGB. It converts HSL to HSV and then uses the steps in the HSV to RGB conversion algorithm.
Alvy Ray Smith (1978): "Color Gamut Transform Pairs", in: ACM SIGGRAPH Computer Graphics, Volume 12 Issue 3, August 1978, pp. 12-19, http://alvyray.com/Papers/CG/color78.pdf
George H. Joblove, Donald Greenberg (1978): "Color Spaces for Computer Graphics", in: ACM SIGGRAPH Computer Graphics, Volume 12 Issue 3, August 1978, pp. 20-25, http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.413.9004
Lee Metrick, et. al. (1979): "Raster Extensions to the Core System", in: ACM SIGGRAPH Computer Graphics , Volume 13 Issue 3, August 1979, pp. III-6-7, pp. III-37-38, http://dl.acm.org/citation.cfm?id=988497.988498
Ken Fishkin (1990): "A Fast HSL-to-RGB Transform", in: Graphics Gems I, pp. 448–449, http://www.gameenginegems.net/gemsdb/article.php?id=751