If the temperature of the Sun rises from T1 = 5600 K 
to T2 = 6600 K, the luminosity will increase by what factor?


     L2       T2^4         6600^4          6600  4
    ----  =  ------  =   ----------  =   ( ---- )
     L1       T1^4         5600^4          5600


 
          =  1.9


so the luminosity increases by roughly 90 percent ...
or almost doubles.