Data Sheet

Appendix A: Window Design Guide

A1: Optical Window Dimensions

To ensure that the performance of the APDS-9301 will not

be aﬀected by improper window design, there are some

criteria requested 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-

9301. 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.

Figure A1 illustrates the two types of window that we

have recommended which could either be a ﬂat window

or a ﬂat window with light pipe.

Figure A1. Recommended Window Design

Table A1 and Figure A2 show the recommended dimen-

sions of the window. These dimension values are based

on a window thickness of 1.0mm with a refractive index

1.585.

The window should be placed directly on top of the light

sensitive area of APDS-9301 (see Figure A3) to achieve

better performance. If a ﬂat window with a light pipe is

used, dimension D2 should be 1.55mm to optimize the

performance of APDS-9301.

Figure A2. Recommended Window Dimensions

WD: Working Distance between window front panel &

APDS-9301

D1: Window Diameter

T: Thickness

L: Length of Light Pipe

D2: Light Pipe Diameter

Z: Distance between window rear panel and

APDS-9301

All dimensions are in mm

Top View

APDS-9301

Photo Light Sensor

D2 D1