A method of determining outdoor characteristics of a photochromic optical article comprising: determining environmental conditions for an area including outdoor air temperature; positioning at least one optical article on a support in the area such that the at least one optical article is facing a first direction; determining a first incident irradiance on the at least one optical article; determining a first surface temperature of the at least one optical article and determining a first spectrum of the at least one optical article; rotating at least one of the following: the at least one optical article, the support, or any combination thereof, such that the at least one optical article is facing a second direction different from the first direction; determining a second surface temperature of the at least one optical article and determining a second spectrum of the at least one optical article; determining a second incident irradiance on the at least one optical article; characterized in that: the determining of the environmental conditions for the area, the determining of the first and second incident irradiances (24, 32), the determining of the first surface temperature of the at least one optical article and determining the first spectrum of the at least one optical article, and the determining of the second surface temperature of the at least one optical article and determining the second spectrum of the at least one optical article are performed at a plurality of different global locations; and generating a prediction model of spectral transmission of the at least one optical article based on the collected data, wherein the model generates a predicted photopic transmission % for the photochromic optical article based on the input of outdoor air temperature and average directional irradiance. determining environmental conditions for an area including outdoor air temperature; positioning at least one optical article on a support in the area such that the at least one optical article is facing a first direction; determining a first incident irradiance on the at least one optical article; determining a first surface temperature of the at least one optical article and determining a first spectrum of the at least one optical article; rotating at least one of the following: the at least one optical article, the support, or any combination thereof, such that the at least one optical article is facing a second direction different from the first direction; determining a second surface temperature of the at least one optical article and determining a second spectrum of the at least one optical article; determining a second incident irradiance on the at least one optical article; characterized in that: the determining of the environmental conditions for the area, the determining of the first and second incident irradiances (24, 32), the determining of the first surface temperature of the at least one optical article and determining the first spectrum of the at least one optical article, and the determining of the second surface temperature of the at least one optical article and determining the second spectrum of the at least one optical article are performed at a plurality of different global locations; and generating a prediction model of spectral transmission of the at least one optical article based on the collected data, wherein the model generates a predicted photopic transmission % for the photochromic optical article based on the input of outdoor air temperature and average directional irradiance. the determining of the environmental conditions for the area, the determining of the first and second incident irradiances (24, 32), the determining of the first surface temperature of the at least one optical article and determining the first spectrum of the at least one optical article, and the determining of the second surface temperature of the at least one optical article and determining the second spectrum of the at least one optical article are performed at a plurality of different global locations; and generating a prediction model of spectral transmission of the at least one optical article based on the collected data, wherein the model generates a predicted photopic transmission % for the photochromic optical article based on the input of outdoor air temperature and average directional irradiance.