This is the 10261st most frequent Japanese word.
電球
Light bulb.
Here, 電球 (denkyuu) is used to refer to a physical light bulb as an item one might need to purchase.
新しい電球を買わなければならない。
I need to buy a new light bulb.
In this context, 電球 (denkyuu) describes the light bulb which has ceased functioning.
電球が切れて暗くなった。
The light bulb burned out, and it became dark.
Here, 電球 (denkyuu) emphasizes the type of the light bulb and its properties, specifically being LED and energy-saving.