# colour.constants.cie Module¶

## CIE Constants¶

Defines CIE constants.

colour.constants.cie.CIE_E = 0.008856451679035631

CIE $$\epsilon$$ constant.

CIE_E : numeric

Notes

• The original CIE value for $$\epsilon$$ is $$\epsilon=0.008856$$, Lindbloom (2003) has shown that this value is causing a discontinuity at the junction point of the two functions grafted together to create the Lightness $$L^*$$ function.

That discontinuity can be avoided by using the rational representation as follows: $$\epsilon=216\ /\ 24389$$.

References

  Lindbloom, B. (2003). A Continuity Study of the CIE L* Function. Retrieved February 24, 2014, from http://brucelindbloom.com/LContinuity.html
colour.constants.cie.CIE_K = 903.2962962962963

CIE $$\kappa$$ constant.

CIE_K : numeric

Notes

• The original CIE value for $$\kappa$$ is $$\kappa=903.3$$, Lindbloom (2003) has shown that this value is causing a discontinuity at the junction point of the two functions grafted together to create the Lightness $$L^*$$ function. 

That discontinuity can be avoided by using the rational representation as follows: $$k=24389\ /\ 27$$.

colour.constants.cie.K_M = 683

Rounded maximum photopic luminous efficiency $$K_m$$ value in $$lm\cdot W^{-1}$$.

K_M : numeric

Notes

• To be adequate for all practical applications the $$K_m$$ value has been rounded from the original 683.002 value. 

References

  (1, 2) Wyszecki, G., & Stiles, W. S. (2000). Standard Photometric Observers. In Color Science: Concepts and Methods, Quantitative Data and Formulae (pp. 256–259,395). Wiley. ISBN:978-0471399186
colour.constants.cie.KP_M = 1700

Rounded maximum scotopic luminous efficiency $$K^{\prime}_m$$ value in $$lm\cdot W^{-1}$$.

KP_M : numeric

Notes

• To be adequate for all practical applications the $$K^{\prime}_m$$ value has been rounded from the original 1700.06 value.