The colour of a bulb is measured in degrees of Kelvin and you will find this measurement on the bulb and/or its packaging. 2700 degrees Kelvin represents warm white and 3400 degrees Kelvin represents cool white.
The colour of a light bulb will affect the ambience in the room. Cool white imitates daylight and is most suitable for working environments like offices and kitchens; where as warm white will complement a more relaxing atmosphere, ideal for bedrooms and living rooms.
The types of light bulb available in order of energy efficiency from best to worst are: LED, Fluorescent Tube, CFL, Halogen, and Incandescent.
In comparison to incandescent bulbs, LEDs use 75% less energy and provide up to 25 times the lifespan; CFLs also use 75% less energy while providing up to 10 times the lifespan.
You will find an energy rating on the packaging of all light bulbs (excluding spotlights and reflector bulbs). The rating goes from A to G with A being the most efficient, and G the least. CFL and LED bulbs are usually rated A, and incandescent bulb are usually E, F or G.
90% of the energy used by incandescent bulbs produces heat not light. Energy saving alternatives save money by not using up so much energy producing heat.
Watts vs. Lumens
Just a few years ago, the wattage of a light bulb is how you knew how powerful it was and how bright its light would be. This is no longer the case. What the wattage really relates to is how much electricity it consumes, so since the introduction of energy efficiency to the light bulb market, wattage can no longer be seen as a representation of the bulb’s brightness. This is where lumens comes in. Lumens is a unit of measurement for the amount of visible light emitted from a source. A 100 watt incandescent bulb will produce about 1600 lumens, the equivalent lumens can be produced from an 18 watt LED bulb.