Spectral Irradiance | pveducation.org

Spectral Irradiance

The spectral irradiance as a function of photon wavelength (or energy), denoted by F, is the most common way of characterising a light source. It gives the power density at a particular wavelength. The units of spectral irradiance are in Wm^-2µm^-1. The Wm^-2 term is the power density at the wavelength λ(µm). Therefore, the m^-2 refers to the surface area of the light emitter and the µm^-1 refers to the wavelength of interest.

In the analysis of solar cells, the photon flux is often needed as well as the spectral irradiance. The spectral irradiance can be determined from the photon flux by converting the photon flux at a given wavelength to W/m² as shown in the section on Photon Flux. The result is then divided by the given wavelength, as shown in the equation below.

F (λ) = Φ E \frac{1}{Δ λ} in SI units

where in SI units:
F(λ) is the spectral irradiance in Wm^-2m^-1;
Φ is the photon flux in # photons m^-2sec^-1;
E and λ are the energy and wavelength of the photon in joules and meters respectively; and

The spectral irradiance is more commonly expressed in terms of wavelength so that:

F (λ) = Φ q \frac{1.24}{λ (μ m)} \frac{1}{Δ λ (μ m)}

where:
F(λ) is the spectral irradiance in Wm^-2µm^-1;
Φ is the photon flux in # photons m^-2sec^-1;
E and λ are the energy and wavelength of the photon in eV and µm respectively; and
q is a constant of 1.6 · 10^-19

spectral irradiance of artificial light sources and the sun

The spectral irradiance of artificial light sources (left axis) compared to the spectral irradiance from the sun (right axis).

Comments

Spectral Irradiance

5 posts • Page 1 of 1

Spectral Irradiance

by stuartb » 13 Jul 2010, 13:04

Link to the page

Last edited by stuartb on 25 Sep 2011, 14:12, edited 9 times in total.
Reason: Edit

stuartb: Registered User; Posts: 28; Joined: 24 Jul 2011, 11:42

Re: Spectral Irradiance

by tracyky2525 » 23 Sep 2011, 10:25

You did not specify the value photon flux to calculate spectral irradiance in the above figure. What's the value of photon flux?

tracyky2525: Registered User; Posts: 1; Joined: 20 Sep 2011, 14:54

Re: Spectral Irradiance

by stuartb » 25 Sep 2011, 12:15

tracyky2525 wrote:You did not specify the value photon flux to calculate spectral irradiance in the above figure. What's the value of photon flux?

The spectral irradiance is usually what is measured. From that you can get the photon flux.

stuartb: Registered User; Posts: 28; Joined: 24 Jul 2011, 11:42

Re: Spectral Irradiance

by Eleftherios » 29 Sep 2011, 09:54

the Y-axis title for spectral irradiance should be uW/m2/um

Eleftherios: Registered User; Posts: 2; Joined: 27 Sep 2011, 04:25

Re: Spectral Irradiance

by stuartb » 30 Sep 2011, 19:37

Eleftherios wrote:the Y-axis title for spectral irradiance should be uW/m2/um

fixed

stuartb: Registered User; Posts: 28; Joined: 24 Jul 2011, 11:42

5 posts • Page 1 of 1

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