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irradiance measurement (w/m2) from the TSL2591

Hi, I would like to know how to get the irradiance measurement from the TSL2591. I mean the sensor gives me LUX but I need w/m2 in the visible and the infrared.

thanks andreaguti

Posts: 3
Joined: Thu May 02, 2019 10:54 am

Re: irradiance measurement (w/m2) from the TSL2591

That's toward the bottom of page 6 in the datasheet:

Depending on which channel you use, there's a nominal counts-per-uW/cm^2 value. Posts: 59131
Joined: Thu Feb 11, 2010 2:51 pm

Re: irradiance measurement (w/m2) from the TSL2591

I didnt understand at all what you said.
I added an image which it is the sensor readings from the arduino when I put the sensor to sense in front of an iron which is 90*C, SO how Can I get the w/cm2 with the data which the arduino gives me
Attachments sensor.PNG (32.02 KiB) Viewed 244 times andreaguti

Posts: 3
Joined: Thu May 02, 2019 10:54 am

Re: irradiance measurement (w/m2) from the TSL2591

The datasheet lists the irradiance values at either 5338 counts per uW/cm^2 or 3474 uW/cm^2 depending on which input channel you use.

Basic math says each count then represents either 1/5338th or 1/3474th of a microwatt per square centimeter.

If the output from the sensor is 52, it means the sensor has detected either 52/5338 or 52/3474 of a microwatt per square centimeter. Posts: 59131
Joined: Thu Feb 11, 2010 2:51 pm

Re: irradiance measurement (w/m2) from the TSL2591

we supposed it but we weren´t sure at all. THANK YOU SO MUCH! andreaguti

Posts: 3
Joined: Thu May 02, 2019 10:54 am

Re: irradiance measurement (w/m2) from the TSL2591

I'm using the TSL2591 sensor for the first time and am trying to understand how to apply the datasheet info to calculate W/m^2. But I'm a bit confused from reading this thread.

From adafruit_support_mike, "If the output from the sensor is 52, it means the sensor has detected either 52/5338 or 52/3474 of a microwatt per square centimeter." BUT the datasheet references channels CH0 and CH1 (column 3) for IR in Figure TSL2591 – 9. CH0 counts output with the 5338 reference and CH1 counts output with the 3474 reference.

Another way to read the datasheet to get IR uW/cm^2 is to choose either CH1 output (52) or CH0 output (137) and divide by their respective references. So, to get IR value, choose from 52/3474 uW/cm^2 OR 137 / 5338 mW/cm^2.

Using the same approach, white light uW/cm^2 would use the 6024 and 1003 count reference with the CH0 and CH1 counts, respectively.

I'm just trying to clarity on how to use Figure TSL2591 – 9. A clear example of how to use output from the two channels and the four count references would be very helpful.

Thanks abferguson

Posts: 1
Joined: Thu Jul 04, 2019 6:18 pm

Re: irradiance measurement (w/m2) from the TSL2591

abferguson wrote:Adafruit TSL2591 Gurus,

Another way to read the datasheet to get IR uW/cm^2 is to choose either CH1 output (52) or CH0 output (137) and divide by their respective references. So, to get IR value, choose from 52/3474 uW/cm^2 OR 137 / 5338 mW/cm^2.

Using the same approach, white light uW/cm^2 would use the 6024 and 1003 count reference with the CH0 and CH1 counts, respectively.

I am so confused now. Where in the data sheet does it give those figures for the Irradiance repsonsivity for IR (CH1)? Working with the June 2018 datasheet for the TSL2591, typical counts per uW/cm2 is shown as 154.1. Shouldn't that be the figure we use to divide the returned IR value from the sensor?

Am I looking at the wrong datasheet?

Regards

Mark MacKenzie Posts: 30
Joined: Tue Aug 05, 2014 8:51 am

Re: irradiance measurement (w/m2) from the TSL2591

Okay, answered my own question and this brings up another one.

Your forum answer was based on a TSL2591 data sheet from April 2013. This datasheet shows the irradiance responsivity to be: .

In the June 2018 TSL2591 datasheet the irradiance responsivity is markedly different: .

So now, how to tell which tsl2591 chip you are selling goes with which count value for irrandiance?? I am interested solely in the IR component in any case but have a number of tsl2591 breakouts from you from a year or so ago.

Since I don't have a way of back checking IR instrumentally I have to rely on the datasheets. I can understand a slight correction of values but this is at least an order of magnitude different and a real problem for me.

I hope you can shed some light (so to speak) on this issue.

Regards

Mark MacKenzie Posts: 30
Joined: Tue Aug 05, 2014 8:51 am

Re: irradiance measurement (w/m2) from the TSL2591

I just checked the tsl2591 datasheet that you have an URL to on the shop product listing and it is the correct latest datasheet of June 2018. So just the datasheet reference used earlier in this thread is stale dated. Boy, what a change in count values though!

Regards

Mark MacKenzie 