So many people are used to thinking about wattage, they forget that word doesn’t measure brightness, but power consumption. They think of needing a brighter bulb, so they seek one that’s a higher number of watts. But that relationship only holds for incandescent bulbs (and, to a degree, halogens). When, as is more and more often the case today, fluorescents or LEDs enter the picture, the situation can become confusing.
A watt is a measure of power, the voltage (in volts) multiplied by the current (in amps). But because of the fact that a higher power consumption by an incandescent bulb causes the filament to become hotter, it glows brighter. That produces a brighter light.
To get a more useful comparison between incandescents and CFLs (Compact Fluorescent Lights) or LEDs, consider instead the amount of lumens the bulb is rated for. A lumen is the amount of light intensity falling on one square foot of area measured one foot away. But don’t worry, you don’t have to get out a light meter and a ruler. That work has already been done for you by the manufacturer.
For example, a 100-watt incandescent bulb will produce about 1,600-1,750 lumens. They vary for many reasons, such as the type of coating on the inside of the bulb, the alloy used for the filament and other factors. By comparison, a CFL may consume only 20 watts, yet produce about the same amount of illumination.
Similarly, a LED bulb which is actually composed of many LEDs, or light emitting diodes, within one enclosure, that produces an equivalent quantity of light may well consume only a few watts of electrical power.
From these numbers it’s easy to see why CFLs and LEDs are becoming more popular. They do cost more up front. But they consume so much less power that, as the bulb prices go down and the cost of electricity rises, they become more attractive. Over 10 years, at 10 cents per kWhr, the savings is approximately $350 for a single LED over the power many incandescents would need.
But the comparisons don’t stop with the amount of electricity consumed and the cost. There are differences among the three in something called color temperature that can form a big part of the choice to go with one or the other.
Human eyes evolved to see in natural daylight and, to an extent, moonlight which is reflected sunlight. The surface temperature of the sun is about 6,000K. (K stands for Kelvin; K = 273 + C, where C is Celsius). Because of the relationship between the temperature of the sun’s gases and light wavelengths along with the effects of the Earth’s atmosphere, the sun produces light that is perceived as approximately white. That relationship between temperature and color gave rise to the term ‘color temperature’.
Incandescents range from a yellowish to a bluish-white, but all do a fairly good job of approximating what our eyes see as ‘natural’, even at the much lower color temperature of approximately 2,700K. Old style fluorescents, because they contain mercury vapor, give off a more greenish cast. But newer CFLs manage to produce a hue much closer to natural white light. LEDs are closer than either.
So, when comparing bulbs look also for the color temperature on the packaging. That hue plays a part in the ease of reading and other tasks that home lighting is designed for. It will affect eye fatigue, and hence the possibility of headaches. It influences the general efficiency with which you can perform those tasks.
Finally, look at the bulb life ratings.
An ordinary incandescent will last from 750-1,000 hours. At the higher number, used 4 hours/day it will last about two-thirds of a year. A good CFL may last between 6,000-15,000 hours, or about 10 years if used the same amount of time. The higher cost is beginning to look like a good deal. An average LED bulb is rated at 50,000-60,000 hours. At 4 hours per day that’s over 40 years of use.
Which is best depends on your budget, your cost of electricity and how often you want or need to buy bulbs. But, as the price of CFLs and LEDs continues to come down, they look better and better, especially for those long-term applications.