LTR-329 lux calculation

icrowe · August 5, 2021, 12:08am

I am using the LTR-329 on a custom PCB. It is correctly reporting ambient light readings from both channels to me. However, the datasheet you publish mentions using the calculation in Appendix A to convert the two different readings to LUX. I’d like to do this, but there is no appendix in the datasheet. Can you provide the additional documentation?

Verna_1353 · August 5, 2021, 12:21am

Hello,

Looking at online posts it appears you have to request this information from Lite On. I have sent a request to the Product Manager to see if we can get this information for you. We will let you know when we get the information.

icrowe · August 13, 2021, 4:10pm

Hello,
It has been more than a week since I made my request - has there been any progress made on getting the extra documentation for the LTR-329?

Ian

Robert_1552 · August 13, 2021, 5:10pm

Hello,

I have sent in to a specialist a request to assist on this, I am sorry for this delay.

David_1528 · August 13, 2021, 10:46pm

Hi icrowe,

While waiting for the actual information from Appendix A, you might want to look at the following links. It looks like a few people have used the information from Appendix A of the LTR-329 to write some code. They both use specific multiplication factors for sensors 0 and 1, depending on the ratio of the raw values returned from each. If you take a look at these, it should give you some ideas of how to proceed.

github.com/pycom/pycom-libraries

Add lux calculations to the LTR-329ALS sensor class

opened 11:37AM - 06 Apr 19 UTC

amcewen

The light sensor on the pySense boards reports two light values from the LTR-329…ALS sensor. Reading the [datasheet for the sensor](https://optoelectronics.liteon.com/upload/download/DS86-2014-0006/LTR-329ALS-01_DS_V1.pdf) that's because there are two sensors sensitive to different wavelengths of light. The datasheet mentions that there is a formula for calculating the lux level from those two readings. It would be good to have the lux reading available from the `LTR329ALS01` class as well as the raw light readings.

github.com

sensebox/SenseBoxMCU-Lib/blob/master/SenseBoxMCU.cpp

/*SenseBoxMCU.cpp
 * Library for easy usage of senseBox MCU
 * Created: 2018/04/10
 * last Modified: 2021/05/07 12:09:31
 * senseBox @ Institute for Geoinformatics WWU Münster
 */

#include "SenseBoxMCU.h"

Bee::Bee() {}

uint8_t Bee::connectToWifi(char *ssid)
{
	nwid = ssid;
	if (!Serial)
	{
		Serial.begin(9600); //check if already connected
		delay(1000);
	}

This file has been truncated. show original

icrowe · August 16, 2021, 11:50pm

Thank you for pointing out that code. I have found and implemented a similar function.

However, I much prefer to understand the theory behind the equation rather than blindly following another implementation. I know nothing about when the corrections might be in scope, nor why they are ignored when the ratio goes out of a certain range.

In addition, that calculation produces a Lux measurement, which is related to the human perception of available light. In our application, we are more interested in the absolute light levels, or perhaps even the light available for photosynthesis. Understanding the math behind the equation will be a great help in establishing that correlation.

It would be really helpful if Digikey could convince Lite-On to provide that datasheet. My direct emails to their tech support email have been ignored so far.

Ian Crowe, P.Eng. 780 885 9201

Proxilogica Corporation