Downlight luminaire

[0001]FIG. 1 is a front perspective view of the ornamental design for the downlight luminaire;

[0002]FIG. 2 is a front view thereof;

[0003]FIG. 3 is a right side elevational view thereof;

[0004]FIG. 4 is a first side elevational view seen rotated 45 degrees from the view of FIG. 3;

[0005]FIG. 5 is a second side elevational view seen rotated 45 degrees from the view of FIG. 4;

[0006]FIG. 6 is a rear view thereof; and,

[0007]FIG. 7 is a rear perspective view thereof.

[0008]The broken line disclosure is for environmental purposes only, and does not form a part of the claimed design.