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Lightness (color)

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Lightness (sometimes called value or tone) is a property of a color, or a dimension of a color space, that is defined in a way to reflect the subjective brightness perception of a color for humans along a lightness–darkness axis. A color's lightness also corresponds to its amplitude.

Various color models have an explicit term for this property. The Munsell color model uses the term value, while the HSL color model and Lab color space use the term lightness. The HSV model uses the term value a little differently: a color with a low value is nearly black, but one with a high value is the pure, fully saturated color.


Relationship between lightness, value, and luminance



File:Lightness approximations.svg
V=10 \sqrt{Y}
Using Table II of the O.S.A. report, Moon and Spencer express the value in terms of the luminance:[8]
V=5 (Y/19.77)^{0.426}=1.4 Y^{0.426}
V=2.357 Y^{0.343}-1.52
V=2.217 Y^{0.352}-1.324
V=2.468 Y^{1/3}-1.636
L^*=25.29 Y^{1/3} - 18.38
Wyszecki simplifies this to:[14]
CIELAB uses the following formula:
where Y_n is the Y tristimulus value of a "specified white object" and is subject to the restriction Y/Y_n > 0.01. Pauli removes this restriction by computing a linear extrapolation which maps Y/Yn=0 to L*=0 and is tangent to the formula above at the point at which the linear extension takes effect. First, the transition point is determined to be Y/Y_n=(6/29)^3 \approx 0.008856, then the slope of (29/3)^3 \approx 903.3 is computed. This gives the two-part function:[15]
f(u)= \left\{\begin{array}{ll}\frac{841}{108}u + \frac{4}{29}, & u \le (6/29)^3 \\ \\
u^{1/3}, & u > (6/29)^3\end{array}\right.
The lightness is then L^*=116 f(Y/Y_n)-16.

At first glance, you might approximate the lightness function by a cube root, an approximation that is found in much of the technical literature. However, the linear segment near black is significant. The best-fit pure power function has an exponent of about 0.42, far from 1/3.

An 18% grey card, having a reflectance of 0.18, has lightness very close to 50. It is called "mid grey" because its lightness is midway between black and white.


  1. Kuehni, Rolf G. (February 2002). The early development of the Munsell system. Color Research & Application 27 (1): 20–27.
  2. Hunt, Robert W. G. (May 18 1957). Light Energy and Brightness Sensation. Nature 179 (4568).
  3. Valberg, Arne (2006). Light Vision Color, John Wiley and Sons.
  4. Priest, Irwin G. (September 1920). An examination of the Munsell color system. I: Spectral and total reflection and the Munsell scale of Value (3).
  5. Munsell, A.E.O., Sloan, L.L.; Godlove, I.H. (November 1933). Neutral value scales. I. Munsell neutral value scale. JOSA 23 (11): 394–411. Note: This paper contains a historical survey stretching to 1760.
  6. Munsell, A.E.O., Sloan, L.L.; Godlove, I.H. (December 1933). Neutral value scales. II. A comparison of results and equations describing value scales. JOSA 23 (12): 419–425.
  7. Newhall, Sidney M., Nickerson, Dorothy; Judd, Deane B (May 1943). Final report of the O.S.A. subcommittee on the spacing of the Munsell colors. Journal of the Optical Society of America 33 (7): 385–418.
  8. Moon, Parry, Spencer, Domina Eberle (May 1943). Metric based on the composite color stimulus. JOSA 33 (5): 270–277.
  9. Saunderson, Jason L., Milner, B.I. (March 1944). Further study of ω space. JOSA 34 (3): 167–173.
  10. Hurvich, Leo M., Jameson, Dorothea (November 1957). An Opponent-Process Theory of Color Vision. Psychological Review 64 (6): 384–404.
  11. Jameson, Dorothea, Leo M., Hurvich (May 1964). Theory of brightness and color contrast in human vision. Vision Research 4 (1-2): 135–154.
  12. Ladd, J.H., Pinney, J.E. (September 1955). Empirical relationships with the Munsell Value scale. Proceedings of the Institute of Radio Engineers 43 (9).
  13. Glasser, L.G., A.H. McKinney, C.D. Reilly, and P.D. Schnelle (October 1958). Cube-root color coordinate system. JOSA 48 (10): 736–740.
  14. Wyszecki, Günther (November 1963). Proposal for a New Color-Difference Formula. JOSA 53 (11): 1318–1319. Note: The asterisks are not used in the paper.
  15. Pauli, Hartmut K.A. (1976). Proposed extension of the CIE recommendation on "Uniform color spaces, color spaces, and color-difference equations, and metric color terms". JOSA 66 (8): 866–867.
ar:إضاءة اللون

be-x-old:Сьвятлыня de:Helligkeit (Farbe) es:luminosidad (color) fr:Clarté (colorimétrie)no:Valør no:Lyshet pt:Luminosidade (cor) ru:Светлота (цвет) zh:亮度 -->

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