[Radiance-general] Mkillum Question

[Terrance McMinn]

Why is the visible light transmittance used with the glass primitive while the visible light transmission value is used in the illum primitive? See below example from chapter 1 pp 29 & 32 of RWR

For Pilkington Optifloat Clear 3mm glass the Visible Light Transmission is 89% (http://www.pilkington.com.au/resources/pilkingtonperformancedatasingleglazing.pdf)

The transmissivity is calculated using: 
	icalc /usr/local/lib/ray/src/cal/cal/trans.cal
	Tn=0.89
	tn
	$1=0.969269687

Therefore for a glass definition you would use something like:
	mod glass window_glass
        0
        0
        3 0.97 0.97 0.97

But when you use mkillum (Rwr chapter 1, page 32 with alteration of the transmission value from 0.88 to 0.89 and transmittance from 0.96 to 0.97) the illum uses the visible light transmission value.
	mod glass window_glass
        0
        0
        3 0.97 0.97 0.97

	skyfunc brightfunc window_dist
	2 winxmit winxmit.cal
	0
	0

	window_dist illum window_illum
	1 window_glass
	0
	3 0.89 0.89 0.89

	window_illum polygon window
	0
	0
	12 ...

Regards 

Terry Mc Minn
Faculty of Built Environment, Art and Design Curtin University of Technology GPO Box U 1987 Perth 6845 Western Australia
Email: T.Mcminn at curtin.edu.au
CRICOS Provider Code: 00301J