Converting Between Light Intensity and Irradiance: How Do They Relate?

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Homework Help Overview

The discussion centers on the relationship between light intensity and irradiance, exploring how to convert between these two concepts in the context of physics. Participants are examining the definitions and units associated with each term.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to clarify the definitions of irradiance and intensity, noting that irradiance is defined as power per area while intensity is power per solid angle. Questions arise regarding the appropriate use of units and the implications of spectral irradiance in specific wavelength ranges.

Discussion Status

The discussion is active, with participants providing insights into the definitions and units of light intensity and irradiance. Some participants are questioning the common usage of these terms and exploring the implications of specific measurements, such as spectral irradiance.

Contextual Notes

There is a noted confusion regarding the units for light intensity and irradiance, with participants discussing the implications of using W(m^-2) in different contexts. The conversation also touches on the importance of bandwidth when interpreting spectral irradiance measurements.

El Flea
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What is the relationship between light intensity and irradiance? How do I convert one to the other?
 
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Strictly speaking irradiance is power/area and intensity is power/solid angle.
Typically irradiance is at the target and intensity is from the source.
But intensity is often used when you should use irradiance - so often they are the same thing,
 
Thanks!
Isn't W(m^-2) the unit for light intensity?
So, if I have, let's say, 1W(m^-2)(nm^-1) spectral irradiance, in the 400nm wavelength range, can I say that I have 1x(10^-9)W(m^-2) light intensity over the same area?
 
El Flea said:
Isn't W(m^-2) the unit for light intensity?
Nope that the unit of irradiance. As I said - intensity is often losely used when you should say irradiance.

So, if I have, let's say, 1W(m^-2)(nm^-1) spectral irradiance, in the 400nm wavelength range, can I say that I have 1x(10^-9)W(m^-2) light intensity over the same area?
It depends on the bandwidth, if you have 1W(m^-2)(nm^-1) then you would have 100W/m^2 over a 100nm bandwidth
 

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