Sorry to nitpick, but "light was made of discrete units that weighed very little and were moving very fast" is not really correct.
First of all, light has exactly zero weight (only a massless particle can travel at exactly the speed of light, and at no other speed for that matter).
Secondly, you're leaving out the wave/particle duality of light, which sort of reminds the Simpson's paradox description of "just two different ways to think about the same data", without which you simply can't fully understand the behaviour of light (or of the statistical system you're looking at).
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).
Well, if we're going to nitpick, light has zero rest mass[0], but does have mass while in motion. This is how solar sails can work, since they use the momentum from the photons.
Weight isn't mass; weight is the force acting on something due to gravity. Gravity effects light, albeit only by a little, so in this sense light has a small but nonzero weight.
I don't believe that's a correct interpretation.
The reason light bends in the presence of gravity is that space time itself is curved, and light follows a "straight line" on that curved space time.
Given weight is defined as `W=mg`, and `m` is `0` for light, light can't have any weight. I think the question is itself incorrect: you can't weigh light because light is not something you can "stop" and put on a balance.
The fact that gravity appears to "attract" light is an illusion. Light only has what is called "relativistic mass" which has very little to do with how we normally think of mass and weight.
> the reason light bends in the presence of gravity ...
This is also why gravity bends the trajectories of massive particles, which also follow geodesics of the curved spacetime (in the absence of other forces).
First of all, light has exactly zero weight (only a massless particle can travel at exactly the speed of light, and at no other speed for that matter).
Secondly, you're leaving out the wave/particle duality of light, which sort of reminds the Simpson's paradox description of "just two different ways to think about the same data", without which you simply can't fully understand the behaviour of light (or of the statistical system you're looking at).