--- ray/doc/man/man1/mkillum.1	2007/12/13 07:03:36	1.7
+++ ray/doc/man/man1/mkillum.1	2008/11/10 19:08:17	1.9
@@ -1,4 +1,4 @@
-.\" RCSid "$Id: mkillum.1,v 1.7 2007/12/13 07:03:36 greg Exp $"
+.\" RCSid "$Id: mkillum.1,v 1.9 2008/11/10 19:08:17 greg Exp $"
 .TH MKILLUM 1 10/6/95 RADIANCE
 .SH NAME
 mkillum - compute illum sources for a RADIANCE scene
@@ -32,17 +32,16 @@ and the secondary source types in RADIANCE.
 If the
 .I \-n
 option is specified with a value greater than 1, multiple
-.I rtrace(1)
-processes will be used to accelerate computation on a shared
+ray tracing processes will be used to accelerate computation on a shared
 memory machine.
 Note that there is no benefit to using more processes
 than there are local CPUs available to do the work.
 .PP
 Remaining arguments to
 .I mkillum
-are passed directly to
+are interpreted as rendering options for
 .I rtrace(1),
-which is used to compute the light distributions for the input surfaces.
+to compute the light distributions for the input surfaces.
 These surfaces can be any combination of polygons, spheres and rings.
 Other surfaces may be included, but
 .I mkillum
@@ -57,8 +56,7 @@ the file names.
 (Note that this character must be escaped from most shells.)
 This is necessary so
 .I mkillum
-can tell where the arguments to
-.I rtrace(1)
+can tell where the rendering arguments
 end and its own input files begin.
 .SH VARIABLES
 .I Mkillum
@@ -221,8 +219,8 @@ BSDF data specified with the
 variable.
 The BSDF will be reoriented relative to the surface as necessary to keep
 the up vector in the vertical plane that contains this axis and the
-surface normal.
-The default value is +Z.
+surface normal, corresponding to an azimuth of 90 degrees.
+The default up vector is +Z.
 .TP
 .BI t =real
 Set the surface thickness to