Until recently, there was only one type of electric light bulbs available - the incandescent bulbs. Well, you could find fluorescent alternatives, but they required special installation, were made from the long tubes which usually didn't blend with the other interior design, and produced a bright cold bluish light that was good for stores or workshops but not the living space. So the homeowner literally had no choice apart from the conventional incandescent bulbs. Luckily, in these latter days the situation has changed drastically.
Firstly, the old good incandescent lights are now produced to be more energy-efficient. The up-to-date variants consume 28% less electric energy than the old ones, while remaining a very cheap option. And secondly, the new advanced types of lighting are now conquering the world. Compact Fluorescent Lamps, known as CFLs, and light-emitting diodes called LEDs are much more energy-efficient and long-lasting light sources. CFL bulbs consume 70% less energy than incandescent bulbs and can work 20 times longer - up to 20000 hours. And LED lights are even better, consuming 90% less energy and living up to 10 years!
When choosing your energy-saving alternative to the old uneconomical bulb, the first thing to pay attention to is the brightness of a new light source. As new types of bulbs consume less electric energy than the old conventional ones, their brightness is no more characterized by their wattage. When we formerly bought the 60W light bulb, we could be sure about its brightness. But now it is not always clear how bright is, for example, 5W LED light or 13W CFL bulb. So now it is better to focus on brightness expressed in Lumens rather than fix on wattage.
There's a simple formula to calculate brightness in lumens: Lumens equal Watts multiplied by lumens per watt value, or Lm=W*Lm/W. Knowing lumens per watt value for different types of light bulbs will give you a possibility to easily calculate brightness of a particular bulb and compare it to the common incandescent one.
Here are the main values you may need: lumens per watt for incandescent light bulbs is 12.5-17.5 lm/W, for compact fluorescent lamps - 45-75 lm/W, and for LED lamps is up to 90 lm/W.
Calculate the brightness of the desired CFL or LED lamp and compare it to the brightness of the common incandescent bulb: 40W incandescent bulb produces 450 lumens, 60W - 800 lumens, and 100W - 1600 lumens.
As you can see, 5W LED lamp produces 5*90=450 Lumens, which equals 40W incandescent bulb. Now manufacturers often specify claims like "5W = 40W" on the packaging of a bulb to rid the consumer of such boring calculations.
After you resolve all the wattage and brightness issues, it's time to think about the light temperature of a new CFL or LED lamp. There's always a Light Appearance label on the packaging. You will find there the light temperature value expressed in Kelvins. For yellowish warm light close to incandescent bulbs look for 2700K value. 3000K will provide warm white light, but not as warm as the previous option. 3500K - 4100K will provide the neutral white light, while bulbs with color temperature of 5000K to 6500K will produce cold bluish light. Which color temperature to choose depends on your needs and preferences, but remember that blue light can negatively affect the sleep.
So now we are done with brightness and color temperature, but there's one more characteristic of modern light bulbs that's worth closer attention. It is called the Color Rendering Index or CRI and describes how correct the colors are under the light of a bulb. The lowest value is 0 and the highest is 100, the higher the better. The conventional incandescent bulbs have the best result with 100, while CFL and LED lamps have a CRI about 80. Still, CRI is not always the best indicator of perception of light emitted by LED lamps, and moreover there are the newest developments that let LED bulbs have a CRI over 90. Anyway, look for the highest CRI available and you'll never lose. Remember to compare CRI of the lamps with the same color temperature, since warm and cold lights render colors differently - simply compare how the environment looks at noon (cold 5500K light) to how things appear at sunset (about 2000K).
There is one more important note concerning CFLs - most of them cannot be used with dimmers. Thus if you are going to install dimmers in your house, or have them already installed, choose LED lights instead. There are some dimmable CFLs, but they are usually too expensive, so LED bulbs will anyway be a better option.
As you can see, modern bulbs have very different features and characteristics. Choosing the most efficient light source will save the energy, so this is the most eco-friendly option. And moreover, this option will be the most cost-saving throughout the years. If you see the ENERGY STAR symbol on the packaging, this means that such bulbs are energy-efficient and will undoubtedly be the smartest purchase.