The ornamental design for a light guideplate used in keyboard, as shown and described.
FIG. 1 is a perspective view of a light guide plate used in keyboard showing our new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is another perspective view thereof; and,
FIG. 9 is another front elevational view shown while in use.
The broken lines showing portions of the light guide plate used in keyboard depict portions of the article and form no part of the claimed design. The broken lines showing LEDs in FIG. 9 depict environmental structure and form no part of the claimed design. The center lines showing on the surface of the light guide plate used in keyboard depict the article is transparent.