In the beginning, God said 'Let there be light', and there was light, and it was generally regarded as a good move - except by some folk with very bad hangovers.
Light made everything more comfortable with less stubbing of toes and whatnot. Those who wanted darkness were free to cover their eyes, a measure which many of the aforementioned hungover folk took. The big drawback with light was this: unless it was daylight and you were outside, there simply wasn't much of it. The moon and stars were fine for necking in the bushes or for cat burglary, but not for a lot more. Fire was all right for a time, but was getting passé.
Enter Thomas Alva Edison. Being a bright lad1, he decided to make an electric powered light source2. In 1879, when he was 32 years old, he succeeded.
Now there are 40, 60 and 100 watt bulbs, and plenty of others too. There are also fluorescent bulbs, halogen bulbs, and even energy-saving bulbs3.
The light bulb has also been the catalyst for many, usually poor, jokes.
Safety Tip: Don't stick your finger in an empty light bulb socket.
1 No pun intended.
2 Light bulbs not being invented yet, a candle metaphorically appeared over his head.
3 Which still consume energy, but that's language for you.