When we bought light bulbs, the salesmen are used to say to us that needing a bright bulb you should choose one with higher number of watts. For example, the conventional 100 watt incandescent light bulb will be brighter than the 60 watt incandescent bulb. It is because higher power consumption the incandescent bulb is, hotter the filament will be, it glows brighter. But, now, as there are more and more high efficient light bulbs come to daily life, the situation is changed.
To get a fully understand of the concept of brightness, we should first learn about the luminous flux (in lumens). A lumen is the amount of light intensity falling on one square foot of area measured one foot away. It is not only a good way to tell us how bright a light bulb can be, but also much helpful when taking comparison between different light sources. For instance, a conventional 100 watt incandescent bulb can create approximate 1,700 lumens, while an 18 watt LED light bulb or a 25 compact fluorescent light bulb can produce the same amount of lumens. With fast development of LED lighting industry, the efficiency of LED can be over 100 lumens per watt in the market. In the lab, efficiency of LED is over 200 lumens per watt. It’s 2 times higher than the efficiency of CFL, and 10 times higher when comparing to incandescent bulbs. Base on this calculation, by replacing incandescent or halogen bulbs by LED, you save over 85% electricity cost. Here is a cost comparison between 100 watt incandescent bulb and its equivalent 18 LED light replacement.
The cost of traditional 100 watt incandescent bulb for a single year (we assume it is on 12 hours per day):
100 watts x 12 hours x 365 days = 438,000 watts
As the electricity charge is $0.2 per KWH, so now, convert 438,000 watts to kilowatts
438,200 watts / 1000 = 438 kilowatts
438 kilowatts X $0.2 = $87.6
The cost 18 watt LED light bulb for a single year (we assume it is on 12 hours per day):
18 watts x 12 hours x 365 days= 78,840 watts
As the electricity charge is $0.2 per KWH, so now, convert 78,840 watts to kilowatts
78,840 watts / 1000 =78.84 kilowatts
78.84 kilowatts X $0.2 = $15.77
We can see clearly that LED bulb can save us$87.6-$15.77= $71.83 for single year use. As the lifespan of LED for lighting is over 50,000 hours (more than ten years).The total electricity bill LED light bulb can save will be tremendous.
But we should not stop the comparisons only at electricity bills. We should take another important consideration, the color temperature, which can form a big part of the choice to go with one or the other. The incandescent lighting sources emit yellowish light, while the old-style compact fluorescent lights product a greenish light because of the mercury vapor. Different from both of them, the LEDs are closer than either. They have the ability to product light waves at specific frequency ranges, so that the colors are more vivid of all light forms.
Although at present, the LED lights are still very expensive. But, as the price continues to come down year by year, they look better and better, especially for those long-term applications.
