Complex sentence: The clock is an integral part of the game, and thus is well lit. However, the original design uses four incandescent light bulbs, which generate a lot of heat that over extended periods can damage the clock housing and PCBs.
Split into simpler sentences: The clock is an integral part of the game, and thus is well lit up. These bulbs generate a lot of heat that over extended periods can damage the clock housing and PCBs.