r
a
t
i
o
o
f
p
a
r
a
l
l
e
l
l
i
g
h
t
t
o
t
o
t
a
l
l
i
g
h
t
:
I
p
/
I
0
.
5
u
p
p
e
r
r
e
f
r
a
c
t
i
v
e
i
n
d
e
x
:
n
1
1
l
o
w
e
r
r
e
f
r
a
c
t
i
v
e
i
n
d
e
x
:
n
2
1
.
5
φ
0
=
π
4
r
a
d
.
=
4
5
°
0
'
0
'
'
φ
1
=
0
.
4
9
0
8
8
3
r
a
d
.
=
2
8
°
7
'
3
1
.
8
2
0
5
'
'
B
r
e
w
s
t
e
r
'
s
a
n
g
l
e
=
0
.
9
8
2
7
9
4
r
a
d
.
=
5
6
°
1
8
'
3
5
.
7
5
6
9
'
'
r
s
=
E
r
s
E
i
s
=
0
.
3
0
3
3
3
7
t
s
=
E
t
s
E
i
s
=
0
.
6
9
6
6
6
3
r
p
=
E
r
p
E
i
p
=
0
.
0
9
2
0
1
3
4
t
p
=
E
t
p
E
i
p
=
0
.
7
2
8
0
0
9