About Compact Fluorescent Light Bulbs, CFLs and Other High Efficiency Light Bulbs
My interest in CFLs stems from my research on the subject of "Climate Change" and a desire to save energy consumption, where possible and where cost effective. CFLs can provide almost 5 times the light output per unit of input power as compared to an incandesent light bulb. As you will see later, a cfl bulb provides 69 lumens per unit watt of input power and an incandescent light bulb provides 14 lumens per unit watt of input power. I first purchased a CFL in the 1990s and was very disappointed with the light output of the bulb. My measurements indicated that it produced less than 50% of its rated output. I still have that bulb and have installed it in a lamp that receives very little use. I also have 2 CFL bulbs in a ceiling light fixture in one of the rooms of my house. The light output is nowhere near that of the 60 Watt incandescent light bulbs it was meant to replace. This fixture has been in place for 11 years. I need to replace these 2 bulbs at least once a year. I would estimate that they never reach 1000 hrs. of use.
First, I need to comment on some terms that I use in my discussion. We want to know how"bright" a light bulb is or we want to know how "bright" an object is when illuminated by this bulb. The manufacturer provides us with the light output of the bulb in lumens. This is the power output of the lamp but in optics it is called "radiance". This tells us how much energy is released from the source. Another quantity of interest to us is how we use this light output. The light falls on a surface and we want to know how "bright" this surface is. A measure of this "brightness" is called "illuminance" and is given as the amount of radiance per unit area, i.e. lumens per square meter. The closer you are to the bulb, the higher this value will be. The illuminance falls off as the inverse square of the distance from the bulb. The quantity of lumens per square meter is a mouthful, so it has been shortened to "lux". One lumen per square meter is one lux. Thus a bulb emitting a radiance of 1000 lumens, results in an illuminance of 1000 lumens per square meter, or 1000 lux, when the area the bulb illuminates is one square meter.
Okay, what is a CFL bulb. First, I took a picture of one of the cfl bulbs I recently purchased.
As one can see, it is a spiral shaped tube sitting on a ceramic base. The spiral tube contains ~ 5 milligrams of mercury and the tube is coated with a fluorescent material. The base contains the necessary electronics for operation of the lamp, along with a glass fuse to prevent overheating of the bulb and to prevent a fire hazard. As power is applied to the lamp, the electric current passes through the mercury vapor resulting in the emission of ultraviolet energy from the mercury. As the ultraviolet energy passes through the fluorescent coating, the bulb emits light with a higher efficiency than an incandescent bulb. The color temperature of the emitted light is determined by the composition of the coating. One of the cfls that I purchased tends to be yellowish, indicating its color temperature might be in the vicinity of 2200 degrees Kelvin, while most of the bulbs seem to be a soft white color, possibly having a color temperature in the vicinity of 2700 degrees Kelvin.
There have been many improvements in the CFL technology since the 1990s. A typical CFL bulb, said to replace a 60 watt incandescent bulb,, uses only 13 watts of input power. This is a power reduction of nearly a factor of 5 times. Thus, I decided to look into this "New" technology. I purchased a GE 13 watt CFL, 60 watt equivalent, at Lowes for $4.50. I placed it in a table top lamp fixture. My first impression was that it was not as bright as the 60 watt incandescent bulb it replaced.
I measured the illuminace of this cfl bulb and found it to be about half the illuminance of a soft white 60 watt incandescent
light bulb under the exact same lighting conditions. As you will see later, this was a defective bulb. Goodbye my $5.00 bill. I found out that 80% of the cfl bulbs are made in China.
I decided to perform some experiments with several other cfl bulbs. I purchased a 13 watt Sylvania cfl for $5.86 at Kroegers. I also purchased a six pack of 13 watt cfls, brand name "Great Value", at Wal*Mart, for $9.88. This reduced the individual cfl bulb cost to $1.70 each, still about 4 times the inital cost of an incandescent light bulb.
I have an inexpensive light meter, reading illuminance in "Lux", lumens per square meter. I also have an inexpensive wattmeter which provides the following data:
- Input Voltage, in RMS Volts
- Current used by the bulb in RMS Amps
- Active Power in Watts
- Apparent Power in RMS Volts x RMS Amps
- Frequency in Hertz
- Power Factor, Actual Power/Apparent Power
- Kilowatt Hour consumption as a function of time
I used 3 bulbs, a 13 watt Great Value cfl bulb, a 13 watt Sylvania cfl bulb and a 60 watt Sylvania Soft White incandescent bulb.
Manufacturer's data for each bulb is as follows:
| Bulb Type |
13 W GV CFL |
13 W Sylvania CFL |
60 W Sylvania Incandescent |
| Input Voltage |
120 Volts |
120 Volts |
120 Volts |
|---|
| Energy Used |
13 Watts |
13 Watts |
60 Watts |
| Radiance Output |
900 lumens |
950 lumens |
850 lumens |
| Bulb Life |
10,000 hrs. |
9000 hrs. |
1000 hrs. |
| Cost |
$1.70 ea. |
$5.86 ea |
$0.40 ea. |
I used a standard type table top lamp for my first test, shown in the photo below. My reading simulated the lamp output illuminating a book which I would be reading, as I sat on an adjacent chair, very close to the lamp.
My data is as follows:
| Bulb Type |
13 W GV CFL |
13 W Sylvania CFL |
60 W Sylvania Incandescent |
| Illuminance |
664 lux |
635 lux |
800 lux |
|---|
| Input Voltage |
121 Volts |
121 Volts |
121 Volts |
|---|
| Current |
0.19 Amps |
0.19 Amps |
0.49 Amps |
|---|
| Active Power |
14 Watts |
13 Watts |
60 Watts |
|---|
| Apparent Power, VA |
23 Watts |
23 Watts |
60 Watts |
|---|
| Power Factor |
.64 |
.59 |
1.0 |
|---|
| Frequency |
59.9 HZ |
59.9 HZ |
59.9 HZ |
|---|
| Life |
TBD |
TBD |
TBD |
|---|
Then I used a lamp which directed the light down onto a reading surface, see photo below. There was no lamp shade to diffuse the light.
My data is as follows:
| Bulb Type |
13 W GV CFL |
13 W Sylvania CFL |
60 W Sylvania Incandescent |
| Illuminance |
1065 lux |
1040 lux |
1007 lux |
|---|
| Input Voltage |
120 Volts |
121 Volts |
120 Volts |
|---|
| Current |
0.17 Amps |
0.17 Amps |
0.47 Amps |
|---|
| Active Power |
14 Watts |
12 Watts |
57 Watts |
|---|
| Apparent Power, VA |
23 Watts |
21 Watts |
57 Watts |
|---|
| Power Factor |
.63 |
.58 |
1.0 |
|---|
| Frequency |
59.9 HZ |
59.9 HZ |
59.9 HZ |
|---|
| Life |
TBD |
TBD |
TBD |
|---|
The data indicates the following:
- The major result is that the cfls are comparable in "brightness" to the incandescent bulb, but have a much reduced power consumption. The two tests which I performed show a strong dependence on the type of lamp fixture used, possibly indicating a difference in the radiation pattern from the two types of lamps.
- The CFL bulbs require a start up time to achieve the illuminance shown in the table. I have shown the illuminance as a function of time in the following graphs. The first graph is for the table top data and the second graph was taken using the other fixture, which directed the light down onto the reading surface.
The graphical data indicates that the maximum radiance of the incandescent bulb is achieved instantaneously. However the CFL bulb requires a warm-up time of 60 seconds to achieve maximum radiance. My opinion is that this is not a problem in most applications. There may be applications where this could be a problem, e. g. in a stairwell application.
- Another point of interest is the power factor.
A power factor of one or "unity power factor" is the goal of any electric utility company. In AC circuits which are totally resistive, it is always one. In AC circuits where there is a phase difference between voltage and current, the power factor is less than one. This results in the requirement for the power company to supply more current to the user for a given amount of power use. Thus the VI value, voltage x current, which is the apparent power, is larger than the actual power value. The utility company will need larger equipment and will suffer additional line losses. I'm sure these costs will be passed on to us, the consumers. In fact, it is my understanding that the utility companies fine commercial users if their power factor is less than one.
The major implication of a power factor which is less than one for the cfl bulb is that it reduces the efficiency of the bulb. Thus a bulb rated with an input power of 13 watts, actually requires about 22 watts of input power for operation, (power factor of .59). Look at the input current levels for each of the bulbs, shown above.
- The achievement of the manufacturer's stated life is yet to be determined, especially when the CFL bulbs are switched on and off in the application in which they are used.
- Cost is a factor. Shopping for the least cost is important. Cost and performance correlation needs to be determined.
I have not commented on the problem of breakage of a CFL bulb and releasing mercury vapor in the area of the breakage. It could be a health hazard since it attacks the nervous system and could cause kidney problems. I don't think the levels are high enough to where it would be a problem in my household. I have been using fluorescent tubes in some of my light fixtures for a long time. Many years ago, when we were raising a family with 4 young children running around, I might have had a different opinion.
I also want to comment on the importance of using a "complete systems approach" to look at your lighting application. My results indicate that just looking at the specifications of the light bulb will not necessarily allow one to choose the bulb they need for their application. I looked at a reading arrangement in my parlor. I have a 3 position couch with 2 table lamps one on each end of the couch. I looked at the illuminance available for reading in the 3 positions. I used 2 each 60 watt Sylvania soft white incandescent bulbs and compared the illumianance available for reading in the 3 different sitting positions to the illuminance available from 2 Great Value 13 watt cfl bulbs. The results are shown below.
| Bulb Type |
2 each 13 W GV CFL |
2 each 60 W Sylvania Incandescent |
| Illuminance, One end of couch |
47 lux |
62 lux |
|---|
| Illuminance, center of couch |
33 lux |
40 lux |
|---|
| Illuminance, other end of couch |
78 lux |
95 lux |
|---|
The incandesdcent bulbs provide about 20 % more reading illumination as compared to the cfl bulbs, even though the cfl bulbs were rated with a slightly higher radiance value, 900 lumens for each of the cfl bulbs and 850 lumens for each of the incandescent bulbs. What this says is that if I need the higher value of illuminance that I received from the incandescent bulbs, I will have to go to a 20 watt or greater cfl bulb. Then the energy savings are not as large as previously indicated. What would be of interest is looking at all the system paremeters such as energy used, energy provided, cost, life etc. considering the entire system, beginning with the manufacturing process and ending with the user.
On the Energy Law passed by Congress and signed by the President
My understanding of this energy law, relative to light sources, is that all light bulbs must use 25% to 30% less energy than today's products by 2012 to 2014. The phase-in will start with 100-watt bulbs in January 2012 and end with 40-watt bulbs in January 2014. By 2020, bulbs must be 70% more efficient.
This will phase out incandescent light bulbs as we know them today. Replacement for these light bulbs include CFLs, discussed above, LED light bulbs and HEI's, High Efficiency Incandescent light bulbs, discussed below. This last item, the HEI bulb, is of high interst to me.
Light Emitting Diode Light Source, LED
The Light Emitting Diode light bulb seems promising. It has the inherent capability of decreasing power consumption to levels well below today's technology. At the present time, it is very costly and the emitted light is directional. One can buy a 10 watt LED light bulb to replace can lights, at this time, for $100.00 each. This bulb uses one 10 watt LED and emits 400 lumens of radiance over a 100 degree solid angle. The directionality makes it seem to be as bright as a 100 watt incandescent bulb which emits 1400 lumens over a 360 degree solid angle. I have 20 can light bulbs in my house, thus at a minimum, it woul cost me $2000.00 to replace them with this bulb. Also, I might need more than 20 bulbs because of the directionality of the emitted light. There are other LED bulbs, which consist of arrays of LED's. The one I priced to replace a 65 watt can light would cost $123.00 per each bulb. In addition, this bulb woud require some modification of the can light holder. I think this technology will require considerable more research to be usable in my household.
High Efficiency Incandescent Light Bulbs, HEI's
The HEI, high efficiency incandescent light bulb is a new product of the GE company. My understanding of this new bulb is that it will use a more efficient filament material than the tungsten filament now used in incandescent bulbs. They have indicated that this bulb will be on the market in 2010 with an efficiency of 30 lumens per watt, double that of today's incandescent bulb, and in 2012 with an efficiency of 60 lumens per watt, four times the efficiency of today's incandescent light bulb. If they achieve their goal, this means that by 2012 we can buy HEI bulbs emitting the equivalent radiance of, say a 100 watt bulb available today, but only using 25 watts of real power. GE's is predicting that these light bulbs will be comparable to today's bulbs in cost. They are attractive because we will not have to replace light fixtures and there will be no danger of a mercury problem, since they will not use mercury.
I guess that I will wait for these new bulbs, which will greatly surpass the requirements of the new law. My hope is that will be produced here in the USA.