The ornamental design for an environmental chamberlightcap, as shown and described.
FIG. 1 is a top perspective view of a environmental chamber light cap according to our new design;
FIG. 2 is an enlarged top perspective view thereof;
FIG. 3 is an enlarged bottom perspective view thereof;
FIG. 4 is an enlarged front view thereof, the rear view being the same;
FIG. 5 is an enlarged right side view thereof, the left side view being the same;
FIG. 6 is an enlarged top view thereof; and,
FIG. 7 is an enlarged bottom view thereof.
The dashed lines in FIG. 1 form no part of the claimed design and are included to show environment. The broken lines encircling the environmental chamber light cap in FIGS. 1 to 3, 6 and 7 indicate the bounds of the claimed design and form no part of the claimed design.