“When most I wink, then do mine eyes best see”
'Wink' here means to close both eyes completely, not to blink one eye as a signal. In Elizabethan usage 'to wink' regularly meant to shut the eyes in sleep or contemplation. The line states the sonnet's central paradox at once: the speaker sees most clearly when his eyes are fully closed.
“they view things unrespected”
'Unrespected' means unnoticed, disregarded, not attended to. The waking eyes pass over ordinary things in the world without truly registering them. The word contrasts with the intense, purposeful seeing the speaker does in sleep.
“darkly bright, are bright in dark directed”
This line packs two oxymorons and a chiasmus (a reversal of terms: A-B / B-A) into one phrase. 'Darkly bright' sets darkness and brightness against each other; 'bright in dark directed' reverses the order. The device enacts the sonnet's central argument in miniature: the speaker's eyes, though shut in the dark, are directed — aimed — toward the bright image of the beloved.
historical The sonnet form“whose shadow shadows doth make bright”
'Shadow' carries two meanings at once: (1) a shade or dark image, and (2) a likeness, copy, or reflected image of a person. The beloved's 'shadow' — meaning the mental image the poet carries of them — makes actual shadows (darkness) bright. The next line extends the pun: 'shadow's form' asks what the real form behind that shadow-image would look like.
“All days are nights to see till I see thee, And nights bright days when dreams do show thee me”
The closing couplet completes the sonnet's inversion of day and night: all days without the beloved are as dark as nights, while nights that bring the dream-vision are as bright as days. This is the volta — the turn or resolution — that clinches the argument. The beloved's absence defines night; the beloved's presence (even as a dream) defines day, regardless of the sun.
historical The sonnet form