I'm not a native english speaker, but I think it doesn't matter.
I see different questions here: What the sentence describes?
A sentence has a purpose, means someone wrote a sentence to express something. It could be: to describe a fact/an observation/a hypothesis or what ever is happening out there. In fact, let's look at what's actually going on there in chronological order:
- The sun burns itself.
- The sun radiates light.
- Lights heats ice
- Heat energy causes molecules of ice moves faster
- hydrogen bonds between ice molecules breaks
- Form changes from ice to water
From observer's point of view:
- We see chemical or other process like: burning, radiating, heating, accelerating, breaking, changing.
- We see substance like: the sun, those lights, those ice, those heat energy, those ice molecules, those hydrogen bonds, those water...
- We could also use other concepts to describe like: task, system, input, output...etc.
It depends on what concept that "writers" chose to use to describe/express.
Same logic, "readers" are free to use other concepts to reconstruct the information carried by the sentence.
So, if I use actor-action concept to describe from what's going on out there.
- I see sun as actor and his action is "burn himself", and he radiates light.
- I see other actors like light, he reach ice, and he heat ice.
- Finally, actor ice acts, he transform into water.