Before he demonstrates an elaborate example of using a laser to push an object, The Action Lab gives an accessible overview of light physics and relativistic mass.
He describes the setup thus: "I make an apparatus in the vacuum chamber that can measure the push of light! And if it doesn't have mass how could it push things, and could you weigh light on a scale?"
He did some of the experiments with a 32,000 lumen flashlight, but he did not show the result with that on his apparatus. That's probably because it's almost impossible to film with the output of a 32,000 lumen flashlight in the shot.