{ RCSid $Id: lumdist.cal,v 1.2 2018/11/21 18:10:45 greg Exp $ }
{
	Conversion from zonal lumens to watts/steradian
}

lum2watt(t0,t1,l) = l / 683 / (omega(t1)-omega(t0)) ;

omega(d) = 2*PI * (1-cos(d*PI/180)) ;