Spectral irradiance, represented as F, is a common way to describe a light source. It is expressed as a function of photon wavelength (or energy). It denotes the power density at a specific wavelength. The units employed for spectral irradiance are Wm-2 µm-1. Here, Wm-2 corresponds to the power density at the wavelength λ(µm) and m-2 pertains to the surface area of the light emitter, while µm-1 signifies the wavelength of interest.
Spectral Irradiance Formula
The spectral irradiance is expressed as a function of the wavelength λ and quantifies the power received by a surface per unit of time for a specific wavelength of light.
Mathematically, it is defined by the equation: F(λ) =Φ E 1/ Δλ
F(λ) represents the spectral irradiance, incorporating the photon flux Φ(m-2sec-1), the energy of an individual photon E(eV), and the wavelength of that photon λ(µm).
The spectral irradiance can also be written in terms of wavelength.
F(λ) =Φ q[1.24/λ(µm)] [1/Δλ(µm)]
Here, F(λ) is expressed as Wm-2 µm-1 and q represents charge which is equal to 1.6 ×— 10-19
In this equation, the number of photons with a specific wavelength striking a surface is denoted by photon flux.
This equation shows how to measure the power contributed by all the received photons per second at a specific wavelength. It involves multiplying the photon flux by the energy of each photon and dividing it by the corresponding wavelength. As a result, this tells the specific amount of power contributed by each individual wavelength.
Solar Irradiance on SDO
The Extreme Ultraviolet Variability Experiment (EVE) aims to evaluate the solar spectral irradiance specifically in the Extreme Ultraviolet (EUV) range. It spans wavelengths from 1 to 1050 ×… (0.1 to 105 nm), along with the crucial hydrogen emission line at 1215 ×….
Moreover, EUV irradiance is absorbed by the atmosphere at altitudes exceeding 100 km. The thermosphere, ionosphere, and nearby space are all significantly affected by changes in EUV irradiance. Measuring EUV irradiance is a simple process that involves evaluating the photocurrent produced by a metal surface exposed to sunlight in space.
Also See: What is Irradiance?
