BrickLink - Part 54930c01 : LEGO Electric, Light Brick 2 x 3 x 1 1/3 with Trans-Red Top and Red LED Light [Electric, Light & Sound] - BrickLink Reference Catalog
LEGO Light Brick Internals and Color LED Replacement - YouTube
LEGO part 54930c01 - Dark Bluish Gray Electric, Light Brick 2 x 3 x 1 1/3 with Trans-Red Top and Red LED Light at BrickScout
BrickLink - Part 54930c01 : LEGO Electric, Light Brick 2 x 3 x 1 1/3 with Trans-Red Top and Red LED Light [Electric, Light & Sound] - BrickLink Reference Catalog