Like Mighty Foot Lights — burned the Red
At Bases of the Trees —
The far Theatricals of Day
Exhibiting — to These —
'Twas Universe — that did applaud —
While Chiefest — of the Crowd —
Enabled by his Royal Dress —
Myself distinguished God —
F507 (1863) J595
In Dickinson's time, theaters used gaslights and limelight to illuminate the stage. Gaslights could be operated at a distance and colored by the use of screens. They were placed at the foot of the stage and adjacent areas. Limelight was a completely different technology that required an attendant at all times to adjust the block of calcium oxide and the gas cylinders that fueled it. It's brilliant light could be focused, and so the best place for an actor on stage would be in the limelight.
In this poem, the stage is set with forest and the footlights have been screened red. Dickinson uses a reverse bit of imagination. Instead of sitting in a theatre imagining that the footlights are rays of the setting sun, she is imagining that a real sunset illuminating the base of real trees is comprised of "Mighty Foot Lights." She develops the conceit as God presenting a show, call it "The Drama of Day," to an audience – the Universe.
The footlights burn red towards the end of the show to signal that the "far Theatricals" are about to end. The universe applauds. The poet, observing all, believes she sees the playwright and producer among the crowd. His "Royal Dress" tips her off to his true identity: God. Maestro!