This filter simulates the photopic response of the human eye to relatively bright light. In the plot below, the circles indicate the design targets -- the desired transmission of the filter. # H$ W3 x+ ~, [2 t1 q1 F
/ @" G+ X0 f9 ~ This design is for normal incidence on a BK7 (ordinary) glass substrate. Two materials are used: SiO2 and TiO2. Starting with a thin, one-layer design, TFCalc's needle/tunneling method produced a sequence of 11 designs of increasing complexity. The design (whose performance is shown above) consists of 32 layers. It matches the entire photopic response curve to within 1%. Phil Baumeister notes that the design can be improved (or simplified) by using a glass whose transmission cuts off near 700 nm.
. @1 Y t8 `& D7 P$ JHere is the design, with the first layer closest to the substrate and thickness given in nm: 4 C' K" P" Y/ m, ]
SIO2 119.32( P) d8 G; J; ~8 [& h- A% e8 F( x
TIO2 10.09
, _ b* k( Q, u% \# P) w" D; } SIO2 32.619 `. Z, g9 e% l g" J
TIO2 79.19 A8 J7 L2 r1 ? m( f
SIO2 19.85
/ } B! i7 ^ z) W5 ` TIO2 9.73. [ v# N# s% K3 U7 E$ e
SIO2 118.20
2 ^* G3 O7 H4 k TIO2 87.90
) j& I0 U* D; F1 B! P5 r. I) u SIO2 128.88
2 w/ p+ k' B( E( m8 f: O TIO2 82.48! D4 u( Q# @- I2 c
SIO2 121.933 i) H K# x1 q
TIO2 83.91" W" B; Y2 e2 k2 C& E3 N3 W& p7 n
SIO2 112.35& p. F1 X6 w' z) ?
TIO2 89.57! d5 ?. I. k7 Y+ T
SIO2 92.26
- G: d" f- f8 o" b! P" [, z TIO2 66.01* p/ m) Z& k" p, F$ C' |6 v. S
SIO2 8.09
% j' L/ Q* G+ I/ X4 k, l# Q TIO2 21.458 Z% |) J5 |" i8 }. A* S9 n
SIO2 103.043 P, T8 X8 v& v d
TIO2 59.41
5 O( C5 K! T' \% x0 x; H SIO2 32.45
/ d$ k6 K" R$ r1 H0 W/ k( Y( T TIO2 15.363 |- S% I0 z* i; T. D
SIO2 98.82
, [* L% O7 I+ A/ @- }; e TIO2 51.98- c( L2 V; k7 C5 Y5 a
SIO2 77.54
- t+ v$ e" x" _; g TIO2 28.26
; n4 {3 h6 e1 V! t" x SIO2 68.84' W' \/ w1 U/ ?; s S
TIO2 49.479 [$ c! y ]; [/ Z4 C" X
SIO2 84.44
$ Z0 r8 s3 F) D# _' ~5 w% D$ U$ x0 ~ TIO2 43.026 x" @0 j6 c t# N5 H9 ~% a
SIO2 53.15& @( N" V4 q; j$ w# x
TIO2 39.34 |