There's been a lot of news regarding our need to replace incandescent light bulbs with Compact Fluorescent Light (CFL) bulbs as it will result in more efficient use of our existing energy resources, which should lessen our need to build new carbon-emitting power plants. I did replace most of my light bulbs with the CFL type but I was curious as to how much energy I'd save using them so I decided to look deeper into them.
The incandescent light bulbs and the light bulb socket we use today is pretty much the same as the ones invented by Thomas Edison back in 1897. The incandescent light bulb generates light from electricity running through a tungsten filament that is vacuum enclosed in a glass bulb. The electricity causes the filament to heat to roughly 4200ºC and glow to give off light. Unfortunately, only about 10% of the energy going into the bulb is used to generate light; the remaining energy is wasted as heat.
The incandescent light bulbs and the light bulb socket we use today is pretty much the same as the ones invented by Thomas Edison back in 1897. The incandescent light bulb generates light from electricity running through a tungsten filament that is vacuum enclosed in a glass bulb. The electricity causes the filament to heat to roughly 4200ºC and glow to give off light. Unfortunately, only about 10% of the energy going into the bulb is used to generate light; the remaining energy is wasted as heat.
The CFL bulb is different in that instead of heating a filament, high-frequency electricity ─ generated from an electronic ballast integrated into the light bulb ─ is used to energize mercury gas enclosed within the bulb. Mercury gas emits ultraviolet (UV) light when energized; the inner walls of the bulb is coated with phosphor, which glows in visible light when hit with UV light. The electronic ballast converts utility ac voltage ─ 120Vrms at 60Hz in North America ─ to high-frequency power, usually around 40 kHz.
One of the complaints about CFL bulbs are that the light emitted is too white and harsh and that they take too long to turn on and emit light. However, the latest CFL bulbs have a warm glow to them, similar to the standard bulb and I find them quite comfortable for reading and working. And these bulbs take only a second or so to light up, which I don't find annoying at all.
The total amount of visible light emitted from a source is provided in units known as lumens. A standard GE Soft White light bulb emits approximately 840 lumens; a 13W GE Energy Smart CFL bulb emits approximately 825 lumens. I haven't noticed any appreciable decrease in light-output from the CFL bulbs; therefore I compared a 60W standard bulb against a 13W CFL bulb. In comparing costs, I used values of $0.27 and $3.77 as the cost of an incandescent bulb and a CFL bulb, respectively; I obtained these values from the GE website.
As the cost of the CFL bulb is substantially more expensive than the standard light bulb, I wanted to determine how long it would take for me to recoup the cost of the CFL bulb from the energy savings. As I needed a light source regardless of the type of bulb it came from, I used the cost difference of the CFL bulb to a standard bulb as my initial investment. Using an energy cost of $0.13kWhr and assuming I'd use the light bulb for approximately 5 hrs a day, I came up with the number of days required to recoup my investment.
It would take approximately 115 days to recoup the cost for the CFL bulb based on an energy cost of $0.13kWhr. This is approximately 3.5 months, which isn't too bad. I then decided to calculate my annual savings using 365 days in a year as shown below.
I would save approximately $11.15 using the CFL over the incandescent light bulb at an energy rate of $0.13/kWhr. Multiply that by the other lights in a typical household and the dollars start adding up! The table below provides payback and savings data at different energy rates.
| Energy Rate, per kWhr | Days To Payback | Annual Savings |
|---|---|---|
| $0.10 | 149 | $8.58 |
| $0.11 | 135 | $9.44 |
| $0.12 | 124 | $10.29 |
| $0.13 | 115 | $11.15 |
| $0.14 | 106 | $12.01 |
| $0.15 | 99 | $12.87 |
As the data above clearly shows, substantial energy savings can be had using CFL bulbs. And the energy saved not only means more money in my pocket but also less CO2 released into the atmosphere and contributing to climate change. All good things!
Now CFL bulbs do contain small amounts of mercury, which is a restricted and hazardous material. According to Energy Star data, each CFL bulb contains about 1.4 - 4 mg of mercury; as a point of reference, old thermometers contained about 500mg of mercury. But the EPA estimates that the US emits approximately 104 tonnes of mercury each year and that most of it comes from coal-fired power plants. Using CFL bulbs, which uses 75% less energy than standard bulbs, would prolong our use of existing power systems without the need to build additional power plants to satisfy our growing energy needs, which will result in less mercury released.
Finally, when CFL bulbs become inoperative and need to be replaced, follow recommended disposal instructions available from the manufacturer or from your local municipality.
Newer and more efficient lighting systems using LED technology are being developed and I'll talk about them in a future post.
According to Energy Star, if every household in the US changed just one light bulb to a CFL light bulb, it would save enough energy in one year to light up 3,000,000 homes. Change your bulbs!!
