Download lightbulb resistance and efficiency AGE Softwhite lightbulb is rated

lightbulb resistance and efficiency
AGE Softwhite lightbulb is rated as follows:
rated power = 60 W ;
rated optical power = 820 lumens (lm)
1 lm = 1/680 W
operating life = 1.5 h
rated operating voltage = 115 V
The resistance of the filament of the bulb, measured with a standard multimeter is 16.7 ohms. When
the bulb is connected into a circuit and is operating at the rated values given above, determine the
resistance of the filament and efficiency of the bulb.
***answer should be 220.4 ohms and 2.009%*** I didn't get the same answer..
820
 1.206 W
680
power out 1.2058


 0.02009  2.009%
power in
60
820 lm 
V2
V 2 115
R

 220.4
R
P
60
2
P  VI 
Efficiency (): The power out is the optical power emitted in lumens (converted to watts). The power
in is the rated electrical power required to light the bulb (60). Efficiency is very poor because most of
the electrical energy converts to heat instead of light.
Resistance: The resistance given is irrelevant. We know that power is (voltage)(current) which can
also be written in another form (using Ohm's law). Rearranging the equation to solve for resistance
and plugging in the values give the correct answer.