This flasher is an ancient design using a 3V lamp. The battery is 6V, with a lot (maybe half) of the power being wasted in the 10 ohm resistor. A LED could be used in place of the lamp, with better, brighter results. Use a 1W LED or else use several regular 5mm LEDs in parallel. The flasher draws very low power when it isn’t flashing, which helps save batteries. If the right parts are chosen, it might work at 4.5V or even at 3V if red, orange, amber or yellow LEDs are used.