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. Skaiserollz89

    A Fourier optics model of a 4f system

    In my system I am trying to represent two lenses. L1 with focal length f1=910mm and the other lens, L2 with focal length f2=40mm. These lenses are space such that there is a distance of f1+f2 between the lenses. I have a unit amplitude plane wave incident on L1. My goal is to find the...
  2. Itay Segal

    Spectral Irradiance Calculation

    Hi everybody, I'm a mechanical engineer working on a phototherapy project, which includes choosing a LED light source that emits a spectral irradiance of 30 µW/cm^2/nm. however, most of the LEDs datasheets giving you the lumens at best. i was able to calculate the irradiance [µW/cm^2] from...
  3. B

    Solid angle in an optics problem (artificial irradiance of the Earth)

    The actual problem can be found as #2 on this link: https://ocw.mit.edu/courses/mechanical-engineering/2-71-optics-spring-2009/assignments/MIT2_71S09_ups1.pdf I rewrote the problem above with the solar irradiance data that they give. My interpretation is of a square 1 m x 1 m plane sitting...
  4. P

    Question about irradiance from a UV lamp

    Greetings all, I'm normally used to researching topics related to biology but I am currently tackling a related side project with UV irradiation, and I don't have much experience with radiometry. I have a compact UV lamp that I am using to irradiate a suspension of small particles (submicron...
  5. WonderfulWorld

    Calculating the Efficiency, total output power and irradiance of LEDs

    Hi Everyone, This is my first post and I hope to work with you on this to gain a fuller understanding. I'm currently designing an LED circuit with 60 3 watt LEDs. Input power is both 120VAC for North American and 230VAC for other countries. I know this is pretty basicbut what is the best way...
  6. Sokolov

    Irradiance of light trapped between two parallel mirrors

    The setup of the problem is shown in the image below. I know that I must add all the contributions of each reflected ray and that its amplitude will be reduced by a factor ##r## each time it is reflected. So after the n-th reflection, its amplitude will be ##E_0r^n##, with ##E_0## the amplitude...
  7. e101101

    Rayleigh Scattering: Blue/Red Irradiance Ratio & Distance

    Hi everyone, does the scattering irradiance ratio between blue/red change with distance with Rayleigh scattering? I would think that it would remain generally constant..
  8. A

    I Calculate Retinal irradiance - from photometric units

    I have been trying to calculate what retinal irradiance value I get with a 1 blue LED system. Since the manufacturer didn´t give the spectral distribution information, I will approximate LED as a monochromatic one (using the 460 nm peak). From the datasheet, the LED intensity range goes from 6...
  9. Nima_khademi

    Calculating a distributed IR source radiant flux

    Hello everyone! does anybody know How can I calculate a distributed radiant flux of an IR source in a space? Is there any software or something?
  10. M

    Irradiance from this infrared light source after a diffuser

    I need to calculate irradiance in a system shown on the image. There is an infrared LED on the left and a diffuser in front of it. I need to calculate irradiance at a certain distance after the diffuser. I think I first have to calculate irradiance at the diffuser. Then multiply it by the...
  11. O

    B Irradiance: difference between distance and the square of the distance?

    What's the difference between distance and the square of the distance? Many Thanks
  12. O

    B Inverse Square Law: Voltage/Current Graphs

    Can a graph of voltage or current on the y-axis over distance represent the inverse square law?
  13. bbbl67

    B Calculating solar irradiance at each planet?

    So I'm getting somewhat weird numbers when trying to calculate the solar irradiance at each planet. Starting with a baseline of irradiance at Earth of 1376 W/m^2, I use the inverse square law against distance. I find the values for Mercury and Mars are really off, while Venus & Neptune are...
  14. RAD2

    Solar Panel Output in Isle of Eigg, Scotland

    Homework Statement I have data for global irradiance on a fixed plane, diffuse irradiance on a fixed plane, global clear sky irradiance on a fixed plane, direct normal irradiance and clear sky direct normal irradiance. I need to calculate the solar power output but I don't know which irradiance...
  15. M

    A Irradiance distribution of projected beam

    Hey folks, I'm having a little bit of trouble shaking the rust off of my radiometry. I'm projecting a circular beam of some known divergence and power onto a surface angled relative to the center of the beam. Say holding a flashlight, with a cone of half angle θ, at my waist some height h off...
  16. N

    Experiment - Flux, Irradiance, wavelength from Temperature

    In my experimental setup I have a purpose built small aluminium tube that has a black layer on the inside to mimic a blackbody. The tube is heated so the inside emits as a blackbody. A separate temperature sensor attached to the tube gives the temperature of the tube. I have a thermopile...
  17. N

    Wavelengths, Flux Density, Irradiance from a temperature measurement

    Homework Statement In my experimental setup I have a purpose built small aluminium tube that has a black layer on the inside to mimic a blackbody. The tube is heated so the inside emits as a blackbody. A separate temperature sensor attached to the tube gives the temperature of the tube. I...
  18. SunThief

    I Off-angle irradiance from Radiant Intensity

    For a light source with a given radiant intensity, I'm confused about the calculation of irradiance at off-angles. I've uploaded a drawing that shows a few spots and their location relative to the source, along with what I understand to be standard calculations. Then at the bottom of the...
  19. Y

    Calculate collector current of phototransistor

    Hello, I'm wondering if it is possible to calculate current the collector current of a phototransistor that is paired with an IR Led? I have an IR Led that is 13.6 cm away from the phototransistor and has a radiant intensity of between 65 mw/sr and 125 mw/sr. The phototransistor that I'm...
  20. SuchBants

    Problem graphing Irradiance and distance experiment

    Homework Statement Used a solar cell and a ray box, altering the distance from the solar cell to the light source in 10cm increments. Did the usual high school experimental controls and repeats. Assuming that the voltage is proportional to the irradiance, I am meant to graph the results...
  21. S

    I Calcuating retinal irradiance from the sun

    Hi all, I want to understand how retinal irradiance (Watts per square centimeters) from the sun is calculated. Some sources calculate 11W/cm^2 like this one...
  22. SunThief

    A Compensate for non-point source irradiance losses on surface

    Hi. To frame things generally, I have a variable indoor light source that shines on an inclined plane. More specifically, I have a 3-D LED matrix that shines light onto a miniature pv array. Essentially, I am using an indoor “sun” to shine on the array. I measure the energy produced, and...
  23. P

    B Irradiance at a point on a surface

    My book states that "irradiance at a point on the outer sphere is less than irradiance at a point on the inner sphere." The formula is simple, it's flux/area. So in case of a sphere its flux/4π*r^2. But my question is what exactly does this formula give? does it give the total flux that...
  24. S

    Irradiance and Isc and Voc of a solar cell

    When irradiance increases what happens to open circuit voltage and short circuit current of a solar cell? Do they both increase linearly? Because temperature affects open circuit voltage, so I'd assume open circuit voltage doesn't increase linearly then...
  25. E

    A Question about Radiance, Solar Flux and Reflectance

    I stumbled upon this equation for a Lambertian uniform target: ##\rho^{*} = \frac{\pi L}{\mu_s E_s}##, where ##\rho^{*}## is the reflectance, ##L## is the measured radiance, ##E_s## is the solar flux at the top of the atmosphere, and ##\mu_s## is the cosine of the sun zenith angle...
  26. O

    Power Irradiance Homework: Find Intensity

    Homework Statement [/B] Homework Equations The Attempt at a Solution I found the expression for the magnetic field, and then the Poynting vector. If i find the intensity, that's the same as finding the average value of the Poynting vector, and the cos^2 disappears... Can you tell me what to...
  27. E

    Confirmation on the Effect of Solar Irradiance

    The Sun emits approximately 1361 watts per square meter on Earth. I read in a book that since the Earth is approximately a sphere and only half of it is being illuminated by the Sun, the solar irradiance at the lit side of Earth is reduced by half (so around 680 watts per square meter). Is this...
  28. G

    IR LED irradiance, radiant exposure and radiance

    Hi! I'm trying to design a device to detect eye blinking while a person is sleeping. I have tried to use TCRT5000 sensor (http://www.vishay.com/docs/83760/tcrt5000.pdf) in the prototype and it works like charm ! However, since the TCRT5000 sensor has an IR emmitter I have some safety...
  29. F

    Calculating irradiance from lux of a halogen lamp

    Hi all. We're currently working on a project and need to know the irradiance hitting a steel sheet some distance away from a halogen lamp. The setup looks like: The problem is we can only measure the lux at the surface of the steel sheet, and I believe in order to convert lux to irradiance...
  30. H

    Modeling: Light irradiance and spatio-temporal decay

    Hello everyone! 1. Homework Statement I want to model the irradiance on a fluid element while it is flowing, from a fixed(above or below) light source that has an irradiance that shows first order decay with time and from x-naught to x-infinity . here are the assumptions: -Laminar flow at...
  31. V

    Estimating irradiance on a square planar surface

    Hi, I have a simple problem. A Lambertian emitter has the shape of a square planar surface, with area Ae=4mm2, total power P=1mW, and is located in yz plane. Another square planar surface, with area Ad=6mm2, is located in the xy plane, at a distance d=10cm to the Ae, and is tilted 20 Degrees...
  32. A

    Photometric and Radiometric measurement concepts

    Hello, I am trying to understand the concepts of photometric and radiometric measurements in an electronic sensor. Various photo sensors based on CCD (Charged Coupled Devices) or CMOS photo diode array technology are available in the market for measurements in Visible Spectrum. Now I want to...
  33. P

    How does Irradiance change with magification?

    Hi everyone, I have an optical test bench. The aim of this test bench is to get a 2 beam interference of the diffracted orders on the image plane. The optical test bench on the whole has a magnification factor of 12.5. 1) I wanted to know how the magnification affects the irradiance. I feel...
  34. T

    Calculating Heat Transfer (Thermal Radiation) to a Shipping Container

    Hello, I am trying to calculate the thermal radiation heat transfer to a shipping container which would be painted white. The purpose is to size an air conditioner for equipment, not living conditions. I have already calculated heat from the other sources. The desired internal temperature is...
  35. P

    Measurement of irradiance of 2 beam interference

    Hi, I have an experiment set up to get two beam interference fringes. I would like to know how I could measure the actual amplitude of the irradiance from the experiment. I have with me a power meter and a CMOS camera. How can I go about this? Thank you
  36. Greg Bernhardt

    What is Irradiance? Definition, Equations & Explanation

    Definition/Summary Irradiance is the power per area of the radiation received by a surface. It is measured in SI units of watts per square meter (W.m^{-2}), or cgs units of ergs per square centimeter per second (erg.cm^{-2}.s^{-1}, often used in astronomy). Equations surface area of...
  37. S

    Measuring Infrared Irradiance for Solar Research

    I'm working on research into the feasibility of separating out the infrared rays above 1200 nm in sunlight for solar power generation. Since silicon cells do not effectively harness these wavelengths, we are experimenting with using interference coatings and a wave guide to separate these waves...
  38. C

    Irradiance of sun in an image?

    Homework Statement What will be the irradiance (power per unit area) in the image, if the Sun's irradiance at the sea level is I = 500W/m^2 Lens is 200mm f Sun is 150x10^9 m away Diameter of sun is 1.4x10^9 m Homework Equations The Attempt at a Solution I know that at the...
  39. E

    Irradiance measurement procedure

    Here's what I'm thinking. The sun is too bright to measure directly with our equipment. If I calibrate without a filter, and capture the reference spectrum with and without the filter, then I can model how the filter changes the spectrum. This way I can capture the sun spectrum with the filter...
  40. heycoa

    Optics | Energy Density, Irradiance

    Homework Statement Suppose a laser produces a pulse of light with duration 1 ns, a diameter of 1 cm, and a total energy of 1 mJ. In free space, the pulse length is this 30 cm, the energy density is 42 J/m3, and the irradiance is 1.3*1010 W/m2. Calculate the length, energy density, and...
  41. JJBladester

    Radiant Intensity vs. Irradiance

    Homework Statement I am having a hard time discerning the difference between radiant intensity and irradiance. I searched PF and found this distinction, but am still confused. Radiance is the power from the source per area into a certain solid angle. Irradiance is the power onto a...
  42. T

    Efficiency, power, irradiance and speed problem

    Homework Statement I've attached the question Homework Equations The problem is I don't know what equation(s) I have to use. The Attempt at a Solution This question my part of my thermofluid dynamics course but I cannot find a formula in my textbook that uses an irradiance...
  43. N

    Can You Calculate Radiance from Irradiance Outputs Using a Spectroradiometer?

    Hi, When you measure irradiance using a spectroradiometer, can you calculate radiance based on the irradiance outputs? How does one measure the angle in cosθ and solid angle Ω in the radiance formula? Thanks!
  44. C

    Apply "Swinging Door" Algorithm to Irradiance Time Series

    How to face a data processig to apply "swinging door algorithm" to a irradiance time Homework Statement I would like to obtain the relevant (irradiance change, time increment) pairs from a irradiance time serie that I have in Excel and Origin. One way to do that is making "swinging door"...
  45. O

    Creating 2D Irradiance Distribution with Exact Scalar Method

    I am trying to create (in matlab) an irradiance distribution in a 2-D array, using the exact scalar method. As of now I have a 2-D array defined as my aperture function and I also have a 2-D array defined as a Gaussian function (light source). I believe that I know how to do this with a...
  46. T

    Computing irradiance at a point

    I'm having trobule trying to work out the solution to a quite simple radiometry problem I've found in the book Physically Based Rendering. The problem is this one a) Compute the irradiance at a point due to a unit-radius disk h units directly above its normal with constant outgoing radiance...
  47. D

    Can Calculus Prove Average Solar Irradiance is a Quarter of Total?

    Homework Statement I am trying to show that the average solar irradiance over Earth's surface is 1/4 of the total solar irradiance using only calculus. Homework Equations Solar Irradiance = S_{o} Irradiance = F = S_{o}cos(θ) The Attempt at a Solution Using geometry, I can easily...
  48. D

    Compute temperature rise from solar irradiance

    Homework Statement (This is not a homework problem; it comes from a real-world problem I'm trying to solve.) Sunlight is falling on an absorptive object. What will be equilibrium temperature of the object given the solar irradiance (I) and the ambient temperature? I = solar irradiance =...
  49. H

    How Do You Convert Spectral Irradiance into Heat Flux?

    I have found an equation in an article which will give me the spectral irradiance due to sunlight as function of longitude, latitude, atmospheric pressure, surface albedo, and precipitable water vapor. I haven't really worked with these sorts of problems before, so my question is how to turn...
  50. G

    How to Calculate the Heat Received by Newly Discovered Extrasolar Planets?

    I was hoping someone would give some advice on the development of this entry on calculating the heat received by newly discovered planets. It is pretty much all there, I guess it just need some clean up for forum quality standards: https://www.physicsforums.com/library.php?do=view_item&itemid=601