Fluorescent tube  

Invented in 1895 by T Edison, the fluorescent lamp, or fluorescent tube also called neon is a low-pressure mercury vapor gas discharge bulb. It uses fluorescence to produce visible light and converts electrical energy into useful light much more efficiently than incandescent lamps.
This type of bulb is highly valued for its luminous efficiency, producing between 50-100 lumens per watt. It is therefore much more efficient than our old incandescent bulbs for a comparable light output.
You can find it in different shapes ranging from tubes to circular shapes.