cara ngitung brapa watt daya yg dipakai oleh resistor caranya dikalikan aja arus dan tegangan di resistor tsb,.
jadi misal dng PSU 12V led 1 watt an diseri 3 brarti tegangan led = 3.3x3 = 9.9v,brarti tegangan resistor = 12 - 9.9 = 2.1v
arus yg diled kalo 1 watt = 350 mA,karena seri,jadi arus led = arus resistor
total daya yg dipakai resistor = 2.1v x 0.35 = 0.735watt..
kalo pake resistor 1/2 watt jelas gosong resistornya,pake yg 1 watt udah cukup,..
kalo mau pake resistor 1/2 watt an bisa aja,tapi diparalel 2,jadi arus 350mA tadi terbagi 2 melewati 2 resistor,.
tapi perlu diingat,kalo 2 resistor yg nilai hambatannya sama di paralel,maka nilai hambatannya jadi 1/2 hambatan nominal,jadi misal resistor 10ohm di paralel dengan 10ohm,jadi nilai hambatan barunya jadi 5ohm,..
semoga bisa bantu,..