<s>
Spherical	O
harmonic	O
(	O
SH	O
)	O
lighting	O
is	O
a	O
family	O
of	O
real-time	B-General_Concept
rendering	I-General_Concept
techniques	O
that	O
can	O
produce	O
highly	O
realistic	O
shading	O
and	O
shadowing	O
with	O
comparatively	O
little	O
overhead	O
.	O
</s>
<s>
The	O
generalized	O
lighting	O
equation	O
involves	O
,	O
among	O
other	O
things	O
,	O
integrating	O
the	O
product	O
of	O
the	O
incoming	O
radiance	O
and	O
the	O
BRDF	O
over	O
a	O
sphere	O
—	O
something	O
that	O
is	O
far	O
too	O
expensive	O
for	O
real-time	B-General_Concept
rendering	I-General_Concept
.	O
</s>
