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.
: }: i" I/ x3 Q
9 a* T3 F A7 W; O3 t 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.
9 A: |2 n/ p q' O; b1 b# mHere is the design, with the first layer closest to the substrate and thickness given in nm:
+ d1 ~7 k3 T" S' \1 V SIO2 119.32
/ \! _7 N: [. X7 U' a: ~ TIO2 10.09" O7 j4 b3 Q c6 Q H
SIO2 32.61
; {8 b- O5 _- ]" H, y% |- m" Q TIO2 79.19
) P# |& d7 Y4 e( M" k SIO2 19.857 [1 n6 y3 m/ i5 [. R2 o
TIO2 9.738 y3 q( K& E4 v$ R
SIO2 118.20
7 |6 C7 z. B' O! s1 i- g5 @/ y+ A TIO2 87.90
* [- h# g: t# Q' f! B SIO2 128.881 x& ]8 q4 A6 G2 b3 C" {
TIO2 82.480 @2 H) [# x9 X5 L( H: a( ?
SIO2 121.93- ]5 d$ s1 x/ }% R; B: W
TIO2 83.91+ w8 x) {3 X& [; `
SIO2 112.35: |3 F; V) b$ V/ a. _) e3 I
TIO2 89.57. y' D+ F. }* z) I% C
SIO2 92.26
% ^5 q/ b5 X; Z7 f TIO2 66.01
1 Q( ^( F0 x, Y3 f- q8 v SIO2 8.09
3 m3 P. Y b7 {; x( W' O: S TIO2 21.45( J7 W" E3 z: ]- `
SIO2 103.042 z/ x! C( i6 z) L! y
TIO2 59.41( a4 }; F k& b! ?
SIO2 32.45
4 r0 U" E. I9 V! R5 W; s: T TIO2 15.368 {% H0 S3 {8 k4 D" g% n" f
SIO2 98.82
5 x# _4 q7 h7 ?, | TIO2 51.98
d% `3 U2 p8 c% n1 {0 B SIO2 77.54
' H+ l4 `1 T$ t4 z6 d TIO2 28.263 m: I) B! D* g5 v( N; X
SIO2 68.84! O+ A* @% T* m
TIO2 49.47
6 l" M. Q% S; ^0 W: u( ^/ a SIO2 84.44
* r, X7 R* x/ H) P# W1 d TIO2 43.02
3 d7 L/ A+ `, h% P T SIO2 53.15
8 O- U' t" H$ [ TIO2 39.34 |