We can't actually see the truth. It's abstract, or something that exists without a concrete, physical presence, like love or grief. But even though we can't see the truth, Dickinson does her best to, ahem, illuminate it for us. She infuses this poem with images of bright things to light up the truth. In line 3, she comes right out and says it: "too bright for our infirm delight." Then she lights us up with the mention of lightning and dazzling. Even the word "Circuit"—though here it probably just refers to going around something—might have you thinking about electricity.
Regardless, the truth is abuzz and bright, so you might want to wear your sunglasses.