Lamp filament used as dummy load is not a valid measurement, because filament resistance varies with conduction/temperature. You need an audio oscillator, dummy load power resistor & oscilloscope, & also need to know ohm's law (I'm not going to try to teach this here). Take it to a shop, which can do this for you accurately for a few bucks, or probably free if you're a good customer.
How to measure the power output?
I need to know the power output of my Roger RS-4 integrated amplifier before buying speakers. However, no indication marked on the amp. How can I measure its power roughly? I tried to measure the sould lever by Sound Level Meter by comparing with my Yamaha VX496 with 65W@8ohm power output. Both RS-4 and VX496 were set at 9 o'clock position. The reading for VX496 is more than RS-4. Does it means RS-4 get less than 65W@8ohm? The same result come out when I measure the level at 12 o'clock postion.