Appendix B: Optical Window Design
for APDS-9002
2.0 Optical Window Dimensions
To ensure that the performance of
the APDS-9002 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-9002. 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 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.
Figures 12(a) and 12(b) illustrate
the two types of windows that we
have recommended which could
either be a flat window or a flat
window with light guide.
FLAT
PHOTO LIGHT SENSOR
Figure 12(a). Window size determination for flat window.
Figure 12(b). Window design of flat window with light guide.
12
HP [ AGILENT(HEWLETT-PACKARD) ]
