Spaceships pushed by LIGHT – the future of space travel?

 You have left me with quite a question that i would love to know the answer to. From my understanding of the physics shown, if you have a bright flashlight pointed at the sail (from something connected to the sail), you should have 0 acceleration due to the photons pushing away from the flashlight but into the sail (this is understanding that the energy of the sun v a flashlight is a substantially different, as in way less energy from a flashlight, but should be scientifically sound in scale) . If this is true then my confusion comes from what happens if you point the flashight away from you? Can a source of light (energy) be an engine?