At 91, the artist Robert Irwin is still evolving his vision, even though he is rarely able to visit the culmination of his efforts—events like the 2016 opening of his installation at the Chinati Foundation in Marfa, a visionary transformation of an abandoned army hospital that took 15 years to complete. During that same span of time, Irwin was experimenting with light shafts, which he fitted with color-saturated fluorescents and attached to blank white walls. While playing with the balance between color and fluorescence, the artist was drawn in by the look of the unlit. The result is this exhibition. Aptly called “Unlights,” it’s a stunning evocation of incompleteness. —C.J.F.