If using an 8 mm diameter bulb for the Sun, the correct distance to Earth from that bulb is 86.4 cm.

That 8 mm diameter bulb (Sun), is proportionally correct with a distance to Earth of 86.4 cm. Therefore, it will still take 8 minutes and 20 seconds for the 8 mm light bulb to radiate its light the 86.4 cm to Earth..