Light Sensor Boards

Light Sensor Boards

As mentioned in the product overview, the different Open Colorimeter instruments utilize different light sensor boards. On this page we will go into these sensors in more detail.

All of the light sensors used with the Open Colorimeter have the same form factor and standard 4-pin JST SH connectors (also called STEMMA QT or Qwiic). They connect to the LED boards in the same way and so can be easily interchanged.

Open Colorimeter TSL2592 Light Sensor Board

Image shows the TSL2591 connected to an LED board

Multichannel AS7341 Light Sensor Board

Image shows the AS7341 connected to an LED board

The AS7341 light sensor is an multichannel light sensor. 8 channels cover the visible light spectrum from 415-680 nm (channels F1-F8). There is also an additional near-IR (NIR) channel and a clear channel (no filter). The visible and NIR channels use filters resulting in the spectal responsivity curves shown in the image below (taken from the datasheet).

Fig 17 in AS7341 datasheet. Normalized Spectral Responsivity

Optical characteristics of the 8-channels in the visible light spectrum. λp = typical center wavelength, FWHM = bandwidth/full-width at half max.

  • channel 1 (Violet): λp = 415nm, FWHM = 26nm
  • channel 2 (Violet): λp = 445nm, FWHM = 30nm
  • channel 3 (Blue): λp = 480nm, FWHM = 36nm
  • channel 4 (Green): λp = 515nm, FWHM = 39nm
  • channel 5 (Green): λp = 555nm, FWHM = 39nm
  • channel 6 (Orange): λp = 590nm, FWHM = 40nm
  • channel 7 (Red): λp = 630nm, FWHM = 50nm
  • channel 8 (Red): λp = 680nm, FWHM = 52n

The 8 channels cover the visible spectrum from approx. 400-675 nm with some overlap between channels. The FWHM (bandwidth) for the channels ranges from 26-52 nm.

We plotted the center wavelength for these 8-channels on the visible light spectrum so you can visualize the channels as well:

Image modified from Gringer - Own work, Public Domain,

UV Colorimeter AS7331 Light Sensor Board

Image shows the AS7331 board

The UV sensor we are using is the ams-OSRAM AS7331 Spectral UVA/B/C Sensor. The AS7331 sensor provides a low noise all in one solution for measuring UV light between 230 and 430nm. It has a huge dynamic range and three separate channels for UVA, UVB and UVC optical radiation.

Some additional features:

  • The sensor communicates via an I2C interface and has 4 adjustable I2C addresses
  • The responsivity of the sensor can be set using Gain (12 steps), conversion time (15 steps) and internal clock frequency (4 steps).  Each of these values is adjusted by a factor of two for each step
  • No extra circuitry is required
Left Panel: Image of the AS7331 sensor from the manufacturer's website; Right Panel: Image of UV detector layout from the AS7331 datasheet
Normalized Spectral Responsivity of the AS7331. Image from AS7331 datasheet.

Open Colorimeter Product Guide

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