Datasheet

11
Appendix B: Optical Window Design for APDS-9007
1.0 Optical Window Dimensions
To ensure that the performance of the APDS-9007 will
not be aected 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 aect the angular response of
the APDS-9007. This minimum dimension that is recom-
mended 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 reection 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 reection (4% on
each side) and an additional loss of energy in the plastic
material.
Figure B1 and B2 illustrate the two types of window
that we have recommended which could either be a at
window or a at window with light pipe.
Z
L
T
D1
WD
Top View
D2 D1
APDS-9007
Light Receving Area
WD: Working Distance between
window front panel & APDS-9007
D1: Window Diameter
T: Thickness
L: Length of Light Pipe
D2: Light Pipe Diameter
Z: Distance between window rear
panel and APDS-9007
Figure B1. Window Size Determination for Flat Window
Figure B2. Window Design of Flat Window with Light Guide
Figure B3 .Recommended Window Dimensions
Table 1. Recommended minimum dimension for optical
window. All dimensions are in mm
WD
(T+L+Z)
Flat Window
(L=0.0)
Flat window with Light
Pipe
Z D1 D1/D2 T/L/Z
1.5 0.5 2.15 - -
2.0 1.0 2.85 - -
2.5 1.5 3.55 - -
3.0 2.0 4.25 2.0/1.2 1.0/1.5/0.5
The window should be placed directly on top of the light
receiving area (active area) of the photo sensor to achieve
better performance and if a at window with a light pipe
is used, dimension D2 should be 1.5mm to optimize the
performance of APDS-9007.
The recommended minimum window dimension is based
on the assumption that the center of the window and the
center of the light receiving of the photo sensor are the
same. It is recommended that the tolerance for assembly
be considered as well. The recommended minimum
window size which will take into account of the assembly
tolerance is dened as:
D1 (min + assembly tolerance) = D1min + 2*(assembly
tolerance) (Dimensions are in mm)
D2 (min + assembly tolerance) = D2min + 2*(assembly
tolerance) (Dimensions are in mm)
Table 1 and Figure B3 below show the recommended
dimensions of the window. These dimension values are
based on a window thickness of 1.0mm with a refractive
index 1.585.