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Appendix B: Optical Window Design for APDS-9004
Figure 6. Recommended Window Dimensions
Optical Window Dimensions
To ensure that the performance of the APDS-9004 will
not be affected by improper window design, there are
some constraints on the dimensions and design of the
window. There is a constraint on the minimum size of
the window, which is placed in front of the photo light
sensor, so that it will not affect the angular response
of the APDS-9004. This minimum dimension that is
recommended will ensure at least a ±35° light
reception cone.
If a smaller window is required, a light pipe or light
guide can be used. A light pipe or light guide is a
Z
L
T
D1
WD
Top View
D2 D1
APDS-9004
Light Receving Area
Figure 5(a). Window Size Determination for Flat Window Figure 5(b). Window Design of Flat Window with Light Guide
cylindrical piece of transparent plastic, which makes
use of total internal reflection to focus the light.
The thickness of the window should be kept as
minimum as possible because there is a loss of power
in every optical window of about 8% due to reflection
(4% on each side) and an additional loss of energy in
the plastic material.
Figure 5a and 5b illustrate the two types of window
that we have recommended which could either be a
flat window or a flat window with light pipe.
Flat
APDS-9004
