The ornamental design for a light accessory for a drawing instrument, as shown and described.
FIG. 1 is a perspective view of a light accessory for a drawing instrument showing our new design;
FIG. 2 is a right side elevational view thereof, the left side being a mirror image thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a rear elevational view thereof; and,
FIG. 6 is a front elevational view thereof.
The broken lines in the drawings are included for the purpose of showing portions of the light accessory for a drawing instrument that form no part of the claimed design.