MMario, quit those clicky things! You'll give those here a dose of reality they're obviously not prepared to handle.

Wolfgang, the sun has a radiation spectrum that is pretty close to that of a 5500 Kelvin black body. How do you want to define average? Half the distance from one end of the visible spectrum to the other, or an average weighted by the energy in a constant narrow wavelength band (X/per Angstrom), or an average weighted by constant energy in a small energy band (X/wavenmber). At any rate to do it quantatively you've got to do it with X = power per unit emittance area or X = photons per unit emittance area, and these will give different averages in each case above (we can ignore the solid angle here because that will be determined by the ratio of the radius of the pupil of the eye to the distance to the sun).

Total normal incident energy on the earth with sun directly overhead, and no clouds or significant polution, is about 1350 watts per square meter (measured, not calulated from effective color temperture).

JennieG, those dreary scientists, with a little help from engineers, brought to us the internet, which gives one unprecedented power to distribute one's ignorance at nearly the speed of light, 299,792,458 meters per second.