Sometimes, "Fern Hill" sounds like a high-priced, no-touch store, where everything is too expensive to buy but great to look at. The speaker uses bright imagery to make the setting beam with life and value, and exemplify his internal joy about being young. Shiny.
Line 3: This line is about night, but the speaker says, "night above the dingle starry." So, although it's dark out, we can see the stars twinkling in the sky. Nothing unusual there, just a country setting where the stars come out at night.
Line 5: He was "Golden" in the heydays of time's eyes. Giving time "eyes" is another example of personification, but also the speaker describes himself as golden, so, in a way, it's like he's the twinkle in time's eye. He's happy and thinks being young is the best.
Line 9: There are "rivers of the windfall light." He's using rural imagery to describe light flowing from the sky. Just as water (rivers) are a source of life and vitality, the speaker is painting a picture of the landscape as a place full of life.
Line 12: The "sun" appears, but what's important is that the speaker describes it as "young once only." This could be an allusion to the speaker himself as "son" that was only young once.
Lines 14-15: The speaker repeats that he was golden. At first, he was golden in the "heydays of time's eyes," but here, he's golden in "the mercy of his means." He's not just repeating that he was happy and in cahoots with time—he's telling us that he was at the mercy of time, too. Time has all the power here, which will be super important later in the poem.
Line 22: There's fire, which is "green as grass." What's unique here is the pairing of fire and grass. The color green binds them together, but we can also see the fire as a source of warmth and happiness for the speaker.
Lines 26-27: Here, horses "flash" in the dark. Of course, this is metaphorical. The horses aren't actually "flashing" but it's a great moment in the poem. Everything at the farm is infused with light, even the evening. What's cool about horses "flashing" is that we can hear and see their quick movements.
Lines 29-30: More shining light. The speaker says, "it was all / Shining." He's talking about the morning, but he could be referencing his whole youth. His descriptions of the landscape double as descriptions of his feelings.
Line 33: The speaker mentions "the birth of the simple light." What's important is that the speaker's comparing his time at the farm to a place so innocent it shines like the beginning of time. In other words, he's describing his youth in terms of creation and possibility.