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.|
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.
Here is the design, with the first layer closest to the substrate and thickness given in nm:
SIO2 119.32 TIO2 10.09 SIO2 32.61 TIO2 79.19 SIO2 19.85 TIO2 9.73 SIO2 118.20 TIO2 87.90 SIO2 128.88 TIO2 82.48 SIO2 121.93 TIO2 83.91 SIO2 112.35 TIO2 89.57 SIO2 92.26 TIO2 66.01 SIO2 8.09 TIO2 21.45 SIO2 103.04 TIO2 59.41 SIO2 32.45 TIO2 15.36 SIO2 98.82 TIO2 51.98 SIO2 77.54 TIO2 28.26 SIO2 68.84 TIO2 49.47 SIO2 84.44 TIO2 43.02 SIO2 53.15 TIO2 39.34
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