1. INTRODUCTION
It was
decided to revise and update CIE Publication No.20 (TC-2.2) 1972.The main reasons for this decision could be summarized as follows.
It hasbecome obvious that the solar spectral irradiance data on which therecommendations in the original document were based were no longer the mostreliable.
During
the past decadea vast amount of new data has becomeavailableboth through modernized me asurement techniques as we1l asimprovedmodelling and parameterization methods. Contrary to the situationsome years ago， the stage has now been reached where results for solarspectral irradiances at ground 1eve1 as measured and those obtained byreliablemodel ing,using extraterrestrial data as basis，show agreement toaccuracies we11 within predictable or estimable uncertainties. It has thusbecomepossible to calculate solar spectral irradiance levels and charac-teristics foranysite onearth provided appropriate meteorological andatmospheric parameters are applied in reliable modeling formulas. This enablesclosesimulation of solar irradiance characteristics for anygeographical site, without the need of having to make in situ measurements.It is also desirable that the number of spectral bands for which integratedsolar irradiance1evels are given， should be increased, especially in theultraviolet region where the degradation coefficient for organic materialincreases nearly exponentially with a decrease in wavelength.
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