What is “pure” energy?
Momentum-density is represented in the stress-energy tensor, and so is directly related to spacetime curvature. Light feels and generates gravity.
A sibling comment points out the hypothetical kugelblitz as an extreme example. In cosmology textbooks you can read about the "radiation-dominated era" of the first roughly 50000 years of the universe where the energy density working strongest against the expansion was dense photons (and neutrinos).
i didn't think about photons having momentum when i was 8, though.
To make a radiometer that runs on photon momentum, you’d need much lighter vanes, probably larger, a harder vacuum, mirrored surfaces, a stronger source of photons, like a laser, and probably most importantly, some way to reduce friction - like a torsion balance.
NASA does solar sail experiments along these lines, e.g. at the Space Power Facility at Plum Brook Station, Ohio - see e.g. https://www.sciencedirect.com/science/article/abs/pii/S00945...