25 November 2005: Changed the MED doses to conform to the paper of Fitzpatrick et al., 1988, after suggestion by an anonymous reviewer. 
11 December 2008: 
The method now applies the CIE vitamin D effective action spectrum. 
Reference: 
Holick, M, R. Bouillon, J. Eisman, M. Garabedian, J. Kleinschmidt, 
 T. Suda, I. Terenetskaya, A. Webb.
CIE Technical Committee 6-54 Technical Report 174 (2006) Action
spectrum for production of previtamin D3 in human skin.
Commission Internationale de l'Eclairage (CIE) Central Bureau.
Vienna, Austria, email: ciecb@ping.at
Also outputs the sunburn exposure time.