We've definitely got a different spin on the whole idea of light in "There's a certain Slant of light." Rather than seeing the light as uplifting and happy, we see it as something oppressive that also has the potential to be somewhat enlightening. So it's kind of good and bad all at the same time in Dickinson's poem.
Lines 1-2: From the very beginning we see light in a context that's not filled with summertime and sunlight. Here it's a "Winter Afternoon," so immediately we sense something slightly odd about this light.
Lines 5-6: The extended metaphor of the initial slant of light transforms into something that becomes more personal and internalized as "Heavenly Hurt." In that paradox we see a bit of the sublime (heaven) with a bit of the earthly (hurt). So it's good and bad at the same time.
Lines 7-8: At this point, the light is illuminating the speaker's internal conflict. There's an "internal difference" she feels, which is also the place where "Meanings are." So we recognize the light as something that illuminates the speaker's unique perception where meanings are determined.
Lines 13-14: Here the mood becomes something like anticipation. The light therefore becomes a bit more alluring and mysterious than in the previous stanzas. And, like death, we're meant to see it as something indefinable in the context of having no absolute meaning.