h = 6.626e-34;
k = 1.381e-23;
c = 2.998e8;
t = 5800;
r_sun = 1.39e9/2;
r_earth = 1.5e11;
f_w = (r_sun/r_earth)^2;
L_sun =@(l) f_w*((2*pi*h*c^2)./l.^5).*(1./(exp(h*c./(l*k*t))-1));
lambda = linspace(0.01, 3)*1E-6;
figure
plot(lambda, L_sun(lambda))
xt = get(gca, 'XTick');
set(gca, 'XTick',xt, 'XTickLabel',xt*1E+6)
xlabel('Wavelength (\mum)')
ylabel('Spectral Irradiance (Wm^{-2} \mum^{-1})')
text(1E-6, 1E9, '$\leftarrow L(\lambda) = f_{\nu} \frac{2\pi hc^2}{\lambda^2} \frac{1}{e^{\frac{something}{something else}-1}}$', 'Interpreter','latex', 'HorizontalAlignment','left')
