Interesting fact: Sunlight has no rest mass, yet it can still push objects. Solar sails work because light carries momentum even though it is not ordinary matter.
The answer: Sunlight has zero rest mass, but its energy has an equivalent mass through E = mc^2. For example, 1 kilowatt-hour of sunlight corresponds to about 4 x 10^-14 kilograms of mass equivalent.
The idea that light can be linked to mass comes from modern physics, not a traditional scale. Sunlight is hard to 'weigh' because what you are really measuring is energy, momentum, and radiation pressure. This matters in astronomy, solar power, relativity, and spacecraft design because light's energy can do real physical work despite having no rest mass.
