More on compact fluorescent lights

I compared a new14w CFL designed to replace a 65W incandescent recessed light (Commercial electric, model  EDXR -30-14) and an new 65W incandescent recessed light (GE Reveal 65) by measuring their spectra with a NIST traceable calibrated spectroradiometer.  In each case the bulb pointed down, like a typical recessed light, with the spectroradiometer measurement point 108 cm below the bulb.  The measurement was repeated seven times for each bulb: first with the spectroradiometer directly below the bulb, then with the spectroradiometer moved about 15 cm horizontally, then 30 cm horizontally…out to about 90 cm horizontal shift. 

Note that the GE Reveal 65 had an “enhanced color spectrum that used a neodymium glass filter to reduce the amount of light in the middle part of the visible spectrum to yield more vivid reds and blues.  I would have been better off with a simpler incandescent lamp for this comparison. 

The first graph below shows the spectral irradiance for the CFL.  Note that most of the irradiance is in the visible part of the spectrum.  The seven curves correspond to the seven horizontal positions, with the highest irradiance being directly below the bulb.  The second graph is the same, but zoomed in to the visible part of the spectrum.

The following two graphs show the same thing for the incandescent lamp.  Notice the dip in the middle of the visible spectrum.  This is due to the neodymium glass filter.  If that filter were not present the total irradiance of the incandescent lamp would have been higher.  I will repeat this experiment at a later date with the simpler incadescent lamp.

 

Irradiance only tells the beginning of the story.  The human eye is more sensitive to some colors than to others.  It is more sensitive to the middle of the visible part of the spectrum than to the red or the blue.  Of course, it is totally blind to the UV and the IR.  So, the irradiance is multiplied by  a Luminosity Function  and a constant to give a measure of how bright a light is.  The following plot shows the typically used Photonic Luminosity function.

The following two graphs show the products of the Photonic Luminostiy function, a constant (683 lux/W/m²), and the spectral irradiance of the CFL and the incandescent bulbs.  The total area under any curve gives the “brightness” for the lamp at a particular horizontal shift.  I have deliberately left the Y axis the same on both graphs to make them easier to compare.  It is clear that the CFL is very bright over two narrow wavelength bands centered on about 545 nm and 620 nm, while the incandescent light is spread more evenly over the visible spectrum.  This is probably why people feel that colors look less natural under a CFL.

After all the graphs and the math, which light is brighter?  It depends on the horizontal position, as shown in the following figure.  The incandescent is brighter directly below the lamp, but the CFL is brighter off to the sides.  This should not be too surprising, because the light from the incandescent comes from a small filament, which is more easily reflected in the same direction than the light from the extended source of the CFL.  But when integrated over all directions, the incandescent and the CFL are probably a very close match, as claimed by the CFL manufacturer.

It would be interesting  to repeat this experiment with bulbs that have accumulated about 1000 hours.  But that is an experiment for another day.

Warm-up time.

I also measured the irradiance of the CFL as a function of time.  This was done for the lamp after it had been off and cool for hours, and again after it had been fully warmed and then allowed to cool for three minutes.   It takes about 4.5 minutes to get to full irradiance for a cold lamp, and about 3 minutes for a warm lamp.  Of course, the warm-up time for the incandescent is essentially zero minutes.

 

 

Conclusions

There are  hundreds of different configurations of CFLs  and incadescent bulbs being used in the world.  My sample is miniscule.  However, some of my numerical results are probably fairly representative, and there are common observations reported by many users. 

As shown above, at least in my case, the 14 Watt CFL was about a bright as the  65 Watt incandescent it was designed to replace.  However, the color quality of the CFL was much poorer.  This poor color quality is a function or the flourescent nature of the lamp, and is likely common to most CFLs. 

The CFL takes a long time to warm up, compared to the instant-on of an incandescent.  The warmup time probably varies from one type of CFL to another.  I have data to indicate that the irradiance vs. time for the warmup minutes can look quite different for a new CFL vs. and an identical CFL with several thousand hours, but that data is not presented here.

As indicated in a previous post, my experience is that a CFL will save money compared to an incandescent that it is designed to replace.  But as shown here, the color quality of the light is worse and there may be an annoying wait for it to warm up.

I will continue to use CFLs where they make sense, but I am also stockpiling some incandescents for the day when they are no longer available by government mandate.  Short duration use of many CFLs reduces their lifetime, and as seen above, it may take several minutes for the CFL to get to full brightness.  So I will use incandescents in closets and storage rooms, etc., and CFLs in the main living areas.

Last comment

I have presented this information as a small part of a large issue.  My endorsement of CFLs, despite some of their drawbacks, is most definitely not support for the government mandate to force us to use CFLs.  I am stockpiling incandescents for certain situations and would suggest that others do the same.  Perhaps the price of LEDs will drop enough to make this issue irrelevant.

Ultimately, I would like to see abundant amounts of energy available to all Americans and to all the people of the world.  Then the issue of light bulb choice would simply be moot.  My fear is that we are moving in the opposite direction.

Compact fluorescent lifetimes

I CHOOSE to use CFLs.  I have strong objections to the federal government DICTATING that these lights be used.  My guess is the CFLs would totally sweep the light bulb market on their own if the lifetime issue, and other nuisance issues were resolved.  But when we are forced to buy CLFs there will little motivation for the CFL manufacturers to resolve these problems.

I started buying compact fluorescent light bulbs in the 1990s, and filled almost every possible light fixture in my house with CFLs.  I had been lecturing my children about the difficult times to come in their adulthood due to lack of energy.  I figured I was making a significant difference by reducing my electricity usage by tens or even hundreds of kilowatt-hours per month.

My goal was to save energy, but I expected that I would also save money.  Although CFLs have a high up front cost, they should pay for themselves in the long run by reducing the electric bill.  I made frequent visits to the hardware store, and always stopped on the lighting aisle to see what new configurations of CFLs were available.

I ignored some nuisances about CFLs in order to serve the greater good.  I noticed, for example, that a 15 Watt CFL that was supposed to replace 65 Watt incandescent was simply not as bright as the 65 Watter.   I noticed that they took a long time to warm up and reach their maximum brightness, and that this warm-up period seemed to get longer as the bulbs aged.  I told myself that I needed to adjust my lighting expectations and habits.  Within less than a year of my first CFL purchase some of the expensive bulbs started dying off.

When I sold that house in 2001, I left a fortune in CFLs in the light fixtures.  I thought I would leave behind a more energy efficient house to help the new owners get a head start on energy efficient living.  Then I spent another fortune equipping my new house with CFLs.  I have managed to keep my electricity usage to about 400 kilowatt-hours per month for a house that shelters 4 people year round (5 in the summer and during college breaks) by consistently replacing failing CFLs.  Otherwise our electricity usage would be about 550 kilowatt-hours per month.

However, I am getting annoyed with dying CFLs.  So about a year ago I started writing the installation dates on the base of each bulb whenever I replaced an old one.  I wanted data, not just memory, to tell me how long the bulbs last. 

Today I replaced my first dated CFL.  It was  installed in a recessed ceiling fixture in my basement on August 12th, 2008,  less than 11 months ago.  It failed in mid-June.  The first picture below shows my hand-written installation date on the base of the bulb.  The second picture shows the “retail product number” (BPCE15R30H/4) which I used to determine the manufacturer.  Oddly, although a brand name (Conserv-Energy) was on the bulb, the manufacturer (Feit) name was not.  I used the retail product number and looked it up at the EnergyStar website

According to the EnergyStar website the lifetime of this CFL was rated at 8000 hours.  It is a 15 Watt bulb designed to replace a 65 Watt incandescent.  We used it for, at most, 8 hours a day for about 10 months, or about 2000 hours.  This CFL saved on the order of 100 kilowatt-hours.  I pay about 10 cents per kilowatt hour when all the taxes and fees are added up.  So, the CFL saved about $10 on my electric bill over its 10 month lifetime, which was  enough to pay for itself with a few dollars to spare.  But it came nowhere near the manufacturer’s claim of saving $48 over its lifetime.

By the way, what fraction of United States energy consumption would be saved if 2/3 of all residential lighting were converted to CFLs?  See question 8 in this quiz to find out.

I will continue to monitor  the failure rate of the many CFL’s in my house.  Based on the first data point, this CFL was a useful investment if you can tolerate the nuisance factors mentioned above.