English: UV sunlight spectrum (on a summer day in the Netherlands), along with the CIE erythemal action spectrum. The effective spectrum is the product of the former two.
# data source: http://www.temis.nl/uvradiation/info/uvindex.html
# solar spectrum: in Netherlands, noon, clear blue sky
action(l) = (l<297) ? 1 : ((l<327) ? 0.0015**((l-297)/30) : 1.5e-3*(1.2e-4/1.5e-3)**((l-327)/73))
set xlabel 'Wavelength (nm)'
set ylabel 'Irradiance (W/m^2/nm)'
set xrange [280:390]
set yrange [8e-5:2]
set log y
set grid
set style data lines
set nokey
set label 'Sunlight spectrum' at 330,0.3
set label "Erythemal action\nspectrum" at 320,0.025
set label 'Effective spectrum' at 300,2.5e-4
set terminal svg enhanced fsize 18
set output 'erythemal_spectrum.svg'
plot \
'sunNL.dat', \
action(x), \
'sunNL.dat' using 1:(action($1)*$2)
unset output