This was written in 50 BCE, nearly two thousand years before Einstein's Nobel winning work proving the discrete qualities of photons.
I'm well aware it's at best a partial description of light.
But it's leagues ahead of Plato's tiny triangles of fire in Timaeus or any other contemporary descriptions.
Also, technically zero mass is very little weight (the least, in fact). And the speed of light is very fast (the fastest). So Lucretius was correct in his statements, if just conservative in the degree to which he stated them (which was in line with the Epicurean commitment to the avoidance of false negatives).
Wave particle duality doesn't really get discussed in Western antiquity outside of a single tangent describing the beliefs of the Peratae who claim the universe has a threefold nature, with the first being continuous and infinitely divisible, the second being a near infinite number of potentialities, and the third being a formal instance. There's a bit of an Everettian quality to their thinking, but outside of its quite broad scope of thought I'm unaware of anyone saying "yeah, reality is both continuous and discrete at the same time" until physicists grappling with contradictory experimental results in the 20th century. The closest in antiquity outside of this group was arguably Plato's theory of forms where the forms were continuous and their physical manifestations discrete, though this is materially different from the idea they are both simultaneously occurring in what's around us (even if Plato's paradigm most likely influenced the much later Peratae).