Low-energy consumption light bulbs now come in a huge variety of shapes, sizes and specifications as per the use. The first generation of replacements was called compact fluorescent lights (CFLs), but they were often dimmer, slower to warm up, and uglier than the old-style bulbs. Instead, many people turned to halogen bulbs, which give a bright light but don't save much energy.
In recent years there has been a dramatic increase in the styles and performance of LED (light-emitting diode) bulbs. These typically use a third less power than CFLs and have replaced them in many domestic and commercial situations as the smart choice for energy-efficient lighting. The latest designs resemble the old incandescent bulbs, with LED filaments inside a clear glass bulb.
Two main questions when buying a replacement bulb will be how much power does it use? and how brightly will it shine? Energy-saving bulbs are available to fill the place of all old-style incandescent bulbs, but use up to 80-90% less electricity. For example an energy-saving CFL bulb only uses 20 watts of power to create the same light as an old 100 watt incandescent bulb. Brightness of an old 60 watt bulb would produce about 650 lumens. Hence, your low-energy equivalent should have at least a similar brightness to give a similar amount of light.
