# How to get a better handle on Spectral Irradiance conversion?

I'm using a computer program to simulate a lightsource.

I can feed my own spectral irradiance values into the program to simulate color rendering accuracy.

The program takes values in electron volt per nano meter. Essentially energy per wavelength.

The problem is that the charts I find online are confusing. Values are in Watt per square meter. It isn't a problem to convert to eV. But what is a problem, are the values on the charts I find. They look like this:

Why is W/m2 divided by nano meters on the Y-axis. And what is the subtraction of the values on the Y-scale about?

Could someone help me out to convert the linked chart to eV/nm? If it is already in eV, why are the values so strange?

I appreciate any help you can provide, and apologize for my "layness".

• The E values are a shorthand way of rendering powers of ten. 4.3E-2 should be read as $4.3 \times 10^{-2}$. – BowlOfRed Aug 28 '15 at 7:54
• That makes sense. But why is W/m2 divided by wavelenght. How do I convert it to eV/nm? – Školstvo Aug 28 '15 at 8:06

Irradiance is flux per area, or normally $W/m^2$. To get spectral irradiance, we want to know the irradiance per range of wavelengths and divide by that range.
If my assumption is correct, then the actual values shouldn't matter at all. All that it would care about is the relative values. You could probably plug in the raw numbers from the chart and not even attempt to convert from $W$ to $eV$.