Hi Maha,

I don’t really know the abbreviations. You should send this question to Radiance mailing list. All honeybee does is calling Radiance gensky or gendaylit to generate the sky.

Here is the exact formula is inside /lib/skybright.cal if this can help you to find the name.

{ RCSid: $Id$ }

{

Sky brightness function for sunny and cloudy skies.

Additional arguments required for calculation of skybright:

A1 - 1 for CIE clear, 2 for CIE overcast,

3 for uniform, 4 for CIE intermediate

A2 - zenith brightness

A3 - ground plane brightness

A4 - normalization factor based on sun direction

A5,A6,A7 - sun direction

}

cosgamma = Dx*A5 + Dy*A6 + Dz*A7;

gamma = Acos(cosgamma); { angle from sun to this point in sky }

zt = Acos(A7); { angle from zenith to sun }

eta = Acos(Dz); { angle from zenith to this point in sky }

wmean(a, x, b, y) : (a*x + b*y) / (a + b);

skybr = wmean((Dz+1.01)^10,

select(A1, sunnysky, cloudysky, unifsky, intersky),

(Dz+1.01)^-10, A3);

sunnysky = A2 * (.91 + 10*exp(-3*gamma) + .45*cosgamma*cosgamma)

* if( Dz - .01, 1.0 - exp(-.32/Dz), 1.0) / A4;

cloudysky = A2 * (1 + 2*Dz)/3;

unifsky = A2;

intersky = A2 * ( (1.35*sin(5.631-3.59*eta)+3.12)*sin(4.396-2.6*zt)

+ 6.37 - eta ) / 2.326

exp(gamma-.563*((2.629-eta)*(1.562-zt)+.812)) / A4;