How much does light weigh?

https://www.youtube.com/watch?v=N60YM4zaLwE

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Practically light has no mass, although, really mass comes from all the energy in an object. Hence m=e/c^2, which was how Einstein proposed the equation originally, in reality only 1% of the mass in your body comes from interactions with the Higgs-field. The rest comes from kinetic and bonding energy in the atoms.

while the particle theory of light suggests that it does have weight, what you is is the photons that have been reflected, not the ones absorbed. only the absorbed ones would contribute additional weight to the wall -- and, over longer periods, you'd have to account for the wall shedding photons when the light is off and thus losing weight.

the practical answer is that light has no measurable weight.

e=mc^2
m = e / c^2

so if you take the amount of energy your flashlight uses, divide that by the efficiency of the lamp in it and put the result into the second formula above, you get the weight of the light