What is Irradiance: Definition and 68 Discussions

In radiometry, irradiance is the radiant flux (power) received by a surface per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used in astronomy. Irradiance is often called intensity, but this term is avoided in radiometry where such usage leads to confusion with radiant intensity. In astrophysics, irradiance is called radiant flux.Spectral irradiance is the irradiance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The two forms have different dimensions: spectral irradiance of a frequency spectrum is measured in watts per square metre per hertz (W⋅m−2⋅Hz−1), while spectral irradiance of a wavelength spectrum is measured in watts per square metre per metre (W⋅m−3), or more commonly watts per square metre per nanometre (W⋅m−2⋅nm−1).

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  1. F

    Understanding the Difference between Radiance and Irradiance

    Radiance, Irradiance? Homework Statement Hi, just wondering if my understanding of the difference between these two is correct?? Homework Equations If radient energy is the energy transported by electromagnetic radiation then radiance is the radient energy crossing a surface per unit...
  2. P

    Calculating Irradiance from BPW21R Photodiode Current

    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...
  3. N

    Irradiance and electric field strength

    Dear physicists, I am desperate. I am using a QM code to propagate a wavefunction of a system that experienced an electric field pulse. However, in literature all values for the electric field strength are given in V/m but the program asks for W/cm^2! I am kind of very confused here and did not...
  4. G

    Effects of Irradiance and Temperature on Solar Modules

    Can you please suggest me some books to read on this topic? It's for my final year project! I would much appreciate it!
  5. mnb96

    Can a Sphere's Irradiance Be Modeled Using a Disk Emitter?

    Hello, I consider a Lambertian spherical emitter with radius R and placed at the point (0,0,h). I would like to compute the irradiance received by the infinitesimal surface patch at (0,0,0) whose normal is the vector (0,0,1). - My question is: is it possible to convert this calculation into...
  6. E

    Solar spectral irradiance at earth's TOA

    (just tried general astronomy board but no luck) I'm trying to reproduce a plot of Sun's black-body behavior like this one: http://en.wikipedia.org/wiki/File:Solar_Spectrum.png Problem is, after I convert the black-body radiance to irradiance, its curve is way too high as compared with...
  7. E

    Solar spectral irradiance at earth's TOA

    I'm trying to reproduce a plot of Sun's black-body behavior like this one: http://en.wikipedia.org/wiki/File:Solar_Spectrum.png Problem is, after I convert the black-body radiance to irradiance, its curve is way too high as compared with measurement. The measurement data is taken from...
  8. B

    Deriving Irradiance Expression

    Homework Statement Electric field for a single pulse of a laser (operating at central wavelength of 800nm): E = E0e^(-(t^2/2a^2))e^(iwt) (the a is sigma and w is omega) Derive an expression for the spectral intensity (irradiance) The Attempt at a Solution One way I know to...
  9. B

    Optics: Electric fields, beams, irradiance

    Homework Statement An electromagnetic wave in a vacuum /w magnetic field of 265 mG. If the wave is spatially confined to a beam with a diameter of .75mm, how much energy is measured by a photodetector with an active area with diameter 5 cm in one second. The Attempt at a Solution...
  10. S

    Yet another doppler question (regarding conservation, time, and irradiance)

    I need the following statements logically-'spellchecked'. The internet, nor books will put it this simply, so I typed up what I feel is a summary, but I don't want to be incorrect in my own mind by doing so. So please proof read my logic and correct it for errors: The doppler effect IS...
  11. J

    What are Radiance and Irradiance and how do they differ?

    Hey, I'm having trouble working out what Radiance and Irradiance are, all the definitions I get are along the lines of something really technical like: "For a point of radiant energy, Radiant Intensity, in a specified direction, per unit projected area: Le=(dIe/dA)*Cos(theta) where A is the...
  12. H

    UV & Irradiance: Calculating UVA Dose for High School Project

    Dear forum members, I would like to ask some help regarding irradiance calculation. I am a high school student doing a project in biology in which I expose drosophila m. (fruit flies) to UVA radiation and I would like to mention in my paper the actual dose that was used. I know that... UV...
  13. P

    Optics - Double Slit Irradiance of Fringes

    [Solved] Optics - Double Slit Irradiance of Fringes Homework Statement A double slit diffraction pattern is formed using mercury green light at 546.1nm. Each slit has a width of 0.100mm (= b), slit separation is 0.400mm (=a). The pattern reveals that the fourth-order interference maxima are...
  14. T

    How can I accurately measure irradiance for my UV sanitization device design?

    hello. I am working to understand and design a UV sanitization device. What is a good resource to learn about irradiance and its relation to distance from a surface. Secondly, in real life, how is irradiance measured? Given a surface area, I would need to specify bulbs of certain...
  15. E

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

    What is the relationship between light intensity and irradiance? How do I convert one to the other?
  16. D

    How do I measure the irradiance of a particular wavelength?

    I am still a high school student and I want to do an experiment on a solar panel. I want filter out red light and then focus is it onto a solar panel and measure various intensities and how it relates to the variation of power output from the solar panel. For this I suppose I should measure the...
  17. J

    How Do You Convert Radiant Power to Irradiance for Solar Radiation Testing?

    Alright, I'm new to the forum, and I've got to say, it is quite impressive. Okay, my question: How do I convert radiant power (uW/10nm/Lumens) to W/m^2? I am conducting a simulated solar radiation test. I need to know the spectral power distribution of a certain metal hallide bulb. The...
  18. S

    Calculate the Solar irradiance

    A solar flare releases 10^25 Joules of energy in one hour over an area amounting to 1% of the area of the Sun’s disk (radius 6.96 x 10^5 km). (a) Calculate the Solar irradiance in W m-2 associated with this flare. (b) Compare this with the black body radiation emitted by the Sun assuming...
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