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[FAQ] OPT3001: OPT300X Family Parts: Industrial design of light sensor with cover glass/window opening

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Part Number: OPT3001

How to design a cover glass or window opening and important considerations

  • Cover material and Window

    Please refer to the application note: http://www.ti.com/lit/an/sbea002a/sbea002a.pdf specifically sections "2 Window Materials" and "3 Field-of-View and Window Size". This gives background on the two main considerations when doing industrial design for the light sensor opening. If no transparent or semi-transparent cover glass is used then only field of view in section 3 needs to be considered. If a cover is used then section 2 discussed this process.

    Cover material (dark glass, transparent glass, other cover materials)

    In many applications a semi transparent or dark cover material is used to hide the light sensor for aesthetics. This reduces resolution of the sensor, but the high resolution of the OPT300x parts still allows good performance with a dark cover glass. For example, the max resolution of 10mLux of the OPT300x family paired with a cover glass with 1% transmission in the visible region will yield an effective resolution of 10mLux/0.01 = 1 lux. The darkness of glass should be chosen depending on the resolution requirements to ensure aesthetic and performance requirements are both met.

    Field of view

    Building on section 3 of the app note on field of view, TI offers a simulator tool to understand the effect of window size and placement of the sensor relative to the hole on resulting field of view. The attached document discusses using the OPT3006 FoV simulator tool for all OPT300x family devices in industrial window design. Download links for the tool are also in the document.

    0435.Using OPT3006 FoV simulator tool for evaluating industrial or mechanical designs.pdf

    Placement

    Placement involves choosing the position of the sensor within the system and choosing the direction to point the sensor. The placement of the sensor and the sensor's field of view will determine the area in which the sensor will sense light. This will vary depending on the application. For example, in display brightness adjustment applications the light reflecting off the screen is what determines how bright the screen needs to be to be easy to view. Thus it is desired to measure the light incident on the display. Usually in this application the best placement is as close to the display as possible. If the screen is viewed directly (viewing angle normal to the display) the light also striking at normal angle is what contributes to glare. However, the screen may also be viewed at different angles and this requires the sensor field of view being sensitive to light striking at angles. Increased field of view also allows the sensor to be less directional and the reading will be more representative of the average brightness level of the environment. In addition to the window size, field of view is also affected by other parts of the system that are in front of the sensor and can block light. In display adjustment for a car dashboard, the dashboard is usually placed in a receding parts of the car dash. This helps with blocking light from striking the display and creating glare. However, if the display is in the middle of this receded area and the sensor is placed near the wall on the side, the wall can block half of the sensor’s field of view and the display may see light that the sensor does not.

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