# Function of solar radiation spectrum

I want to calculate the area under a curve between 250nm to 300nm to find the irradiance in [W/m2], to do this I think must find the function of Spectral Irradiance (sunlight out the atmosphere, yellow function) and then apply integral between the two points, in that case, how is this function? If that is not the case, how calculate the irradiance between 250nm to 300nm?