Calculating Irradiance from BPW21R Photodiode Current

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Discussion Overview

The discussion centers on calculating irradiance (W/m²) from the current produced by a BPW21R photodiode in a transimpedance amplifier circuit. Participants explore the implications of using sensitivity values provided in the photodiode's optical characteristics, specifically addressing the absence of a direct spectral sensitivity value (A/W).

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether it is appropriate to use the sensitivity value (nA/lx) to derive an A/W value for the BPW21R photodiode.
  • The calculation presented involves multiplying the sensitivity by lumens per Watt and dividing by the area, but the validity of this approach is not confirmed.
  • Another participant suggests that the "R" in BPW21R likely indicates RoHS compliance and asserts that it should be functionally compatible with the BPW21, though this does not directly address the irradiance calculation.
  • A request for comments on the calculation method indicates ongoing uncertainty and invites further input from others.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the appropriateness of the calculation method for determining irradiance from the photodiode current, and multiple viewpoints regarding the compatibility of the BPW21R with the BPW21 are presented.

Contextual Notes

The discussion lacks a definitive spectral sensitivity value for the BPW21R photodiode, which complicates the calculation of irradiance. The assumptions underlying the calculation method and the implications of using nA/lumen values remain unresolved.

Who May Find This Useful

This discussion may be of interest to those working with photodiodes in irradiance measurements, particularly in contexts where spectral sensitivity data is not readily available.

pochd
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I am using a BPW21R photodiode to measure irradiance instead of a BPW21 photodiode in a pyranometer circuit that could be found in the pdf link below. How should I calculate irradiance(W/m^2) from the current produced in a transimpedance amp circuit if there is no Spectral sensitivity(Ampere/Watt) value given?


Is it ok to use the sensitivity value (nA/lx) given in the optical characteristics to get an A/W value? (0.81) Below is the calculation i used:

Sensitivity x lumens/Watt * Area^-1

9x10-9 [A*m^2/lumen] x 683 [lumens/Watt] x (7.5x10-6)^-1 [m^2]

Pyranometer Circuit Design

http://www.mdpi.com/1424-8220/9/6/4615/pdf

Photodiode Datasheet

http://www.vishay.com/docs/81519/81519.pdf
 
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Pochd,

Welcome to PF!

You can contact Vishay, but I am 99.9% certain the "R" simply denotes RoHS compliance, functionally it should be 100% compatible with the BPW21.

Fish
 
Pochd,

Welcome to PF!

You can contact Vishay, but I am 99.9% certain the "R" simply denotes RoHS compliance, functionally it should be 100% compatible with the BPW21.

Fish
 
Any comments on the calculation of irradiance using the nA/lumen value?
 

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