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CFL Fluorescent Light Bulbs: More Hype Than Value

Recently by Paul Wheaton: Organic Lawn Care for the Cheap and Lazy

I used to like fluorescent lights and then I changed my mind.

As the years passed, I found more and more folks like me, and more and more reasons to be uncomfortable with fluorescent lights. When some people see that I don’t use them, they try to tell me about how great they are. When I try to explain why I prefer incandescent, I nearly always get a dismissive wave – signaling that I am clearly a fool and whatever tripe I am about to utter is clearly not worth their time. This article represents a glimpse into that tripe.

If you leave all of the lightbulbs in your house on 24/7, then replacing all of the incandescent light bulbs in your house with CFL light bulbs will save you money. For people that typically leave lights off when not in use, it turns out that incandescent light is cheaper than fluorescent light – the exact opposite of what we have been told all these years.

With a little knowledge, you can stop wasting money on CFLs. Both in the short term and the long term. The long term stuff includes tax issues and the toxicity tie-in which leads to superfund cleanups and medical bills.

In a nutshell:

CFL bulb longevity

Supposedly, a fluorescent light bulb will last ten times longer than an incandescent. It says so right on the box. When my CFL bulbs seemed to burn out faster than my incandescent bulbs, I thought I was doing something wrong or I had bad batch of bulbs. Most of the people I visited with about CFLs reported that they were experiencing something similar. So I started to do more research.

Here is a “100 watt long life incandescent light bulb” on amazon for $1.52. It says that it has a lifespan of 25,000 hours. Apparently, a standard bulb has a lifespan of 1000 hours. Here is a “100 watt equivalent CFL” on amazon for $2.87. It claims a lifespan of 8,000 hours. I searched for “CFL 100” and came up with bulbs claiming a lifespan of 6,000 to 10,000 hours. The claim of 8,000 hours seemed the most common.

Fluorescent light bulbs don’t do well when they are turned on and off a lot. While this is true of incandescent bulbs as well, fluorescent bulbs are far more sensitive this way. Wikipedia says “In the case of a 5-minute on/off cycle the lifespan of a CFL can be reduced to ‘close to that of incandescent light bulbs’.” Most household light bulb use is less than five minutes: a trip to the bathroom; looking in a closet; a snack from the kitchen; find something in the bedroom; etc. Optimal use for a fluorescent light is to be left on all the time at temperatures between 50 and 80 degrees (F). You can still experience savings when an area needs to be illuminated by artificial light for ten hours or more at a time. But for most households, the need is for a few lights to be on for an hour in the morning and two to five hours at night, and most lights to be on for one to ten minutes as needed. If you try to leave the light on longer so the bulb will last longer, the electricity savings are then lost. A more accurate longevity statement would be “250 to 10,000 hours depending on use.”

In this mythbusters light bulb video a group of different light bulbs are turned on and off every two minutes for six weeks.

This makes for 504 hours of time that the lights had power – although they probably burned out before the 504 hour mark. The incandescent and both of the fluorescents were dead at the end of six weeks. I suspect that the 1000 hour rated incandescent outlasted the 10,000 hour rated fluorescent – but they don’t say. The important lesson here is that the fluorescent light bulb failed before reaching 5.1% of its rated lifespan (and, yes, the incandescent failed before reaching 51% of its rated lifespan).

Short tangent: A friend of mine told me about how boats long ago used incandescent bulbs that were re-usable. The bulbs all had a way of opening them up and replacing the filament. And the boats carried a light bulb repair kit, complete with a bunch of filaments. Imagine: a light bulb that lasts forever. You just have to mend it with a bit of filament every couple of years. Maybe filaments come in 100 packs for $5.

CFL manufacturers exaggerate brightness

The author of this CFL article used a light meter to measure the light coming from four different 60 watt incandescent bulbs and five different fluorescent bulbs claiming to have light equivalent to a 60 watt bulb. The result was that the average incandescent bulb was 64.5% brighter. And the results were shockingly consistent.

CFL decrease in lumens over time

Fluorescent lights put out less light over time. I remember when I used to use fluorescent bulbs, when I replaced a bulb of the same power, the new bulb seemed about twice as bright as the old bulb. But when I replace an incandescent bulb, they seem about the same level of bright. Is it possible that all of the money saving claims of the CFL producing four times more light per watt is based on a brand new bulb? Maybe they should say that it produces the same light as a 60 watt incandescent bulb in the beginning and a 30 watt incandescent bulb at the end. It turns out that my instincts were not too far off. From wikipedia: “CFLs produce less light later in their lives than when they are new. The light output decay is exponential, with the fastest losses being soon after the lamp is first used. By the end of their lives, CFLs can be expected to produce 70-80% of their original light output.”

net CFL light per watt correction

At this point I need to combine the light per watt information we have so far. To do this, I want to imagine a room (A) with 100 incandescent lightbulbs, and another room (B) with 100 CFLs. The goal is to figure out how many more CFL lightbulbs we need to add to B have the same average light as A. Which is what is advertised on the CFL box.

Starting with the exaggeration, we have to add 64.5 bulbs. So we now have 164.5.

Next we have the issue of the bulbs giving off less light as time passes. So if the light starts at 100%, quickly degrades to 80% and then slowly ends up 75%, then a rough average approximation of that is 80%. It’s as if I put in five light bulbs and one does not work. To go from four working lights to five, I need to add one. From the perspective of the four bulbs, I need a 25% increase. 25% of 164.5 is 41.125. This brings us to a total of 205.625.

To get the brightness claimed by the CFL manufacturer, we need more than twice as many CFLs. I’m going to use the number 105.6 and call this “the CFL brightness adjustment”.

There are claims that a CFL gives off three to five times more light per watt than incandescent. A 10 watt CFL claims to put out the same amount of light as 40 watt incandescent bulb. Four times more light. When we factor in “the CFL brightness adjustment”, we need 1.056 more light bulbs. In the end, this means that the CFL is 1.95 times as bright as the incandescent. This is the number I am going to use for the rest of this article as the actual light per watt improvement.

CFL performs poorly for first two minutes

First, a fluorescent light uses about 20 times more power in the first second to get started. So, for a two minute cycle, the total power consumed is 16% higher. Then it can take one to three minutes to reach full brightness. At first, the light might be giving off only 30% of it’s maximum light. So if you are only using the light for a minute or two, the efficiency of light per watt is worse than incandescent. If the light is in a place where you never have the lights on more than a minute or two, CFLs are far more expensive than incandescent. Both for the cost of the bulb and for the cost of the electricity.

Between the mythbusters thing and the wikipedia article, I think it is fair to say that if 100% of the use of a CFL is a series of two minute jobs, the overall lifespan of the bulb is closer to 500 hours. Probably less.

Three minutes seems the most common. So if we assume 30% at time zero, and 80% at two minutes, that makes for an average of 55%. When you work in the extra power, this makes the two minute scenario roughly double brightness adjustment.

CFL performs poorly in the cold

Most fluorescent lights don’t work in the cold. Some fluorescent lights have been modified with special ballasts to tolerate temperatures below freezing, but they will still fail when it gets to, say, zero (F), although I have heard of some that will go a little colder.

CFL bulbs are toxic

Every fluorescent light bulb contains toxins. Primarily mercury. The toxin issue is severe enough that you are not supposed to throw them away when they die. You are supposed to dispose of them in an appropriate facility. I guess people are supposed to drive their light bulb to the facility for proper disposal? I would call that an extra expense for CFL – your time has value and the fuel to drive there costs something (tiny CFL funeral arrangements are optional). How many people know that fluorescent bulbs are not to be thrown in the garbage? I suspect that 99% of dead fluorescent light bulbs get thrown in the garbage and their toxins can do their toxic thing.

When a CFL breaks in your home, that toxin is now in your home. Do NOT touch the mercury! Cleanup and proper disposal is far too complicated to go into in this article. Here is a stressful story.

A case has been made about the toxicity where if you figure in the amount of energy saved by a fluorescent light bulb, and you work in the average amount of power that comes from coal, and the amount of mercury that is in coal, then if you assume that a fluorescent bulb lasts 10,000 hours, then there is less mercury overall with the fluorescent path.

Put a different way:

From wikipedia: assume 8000 hours of light. The incandescent will be responsible for 5.8 mg of mercury pollution from coal plants, and zero from the bulb. The fluorescent will be responsible for 1.2 mg from the coal plants and 0.6 mg in the bulb.

I have two concerns with this:

    Concern 1: A CFL has three to five milligrams of mercury per bulb. The report elected to count only 0.6 mg because that is what they estimate would leak out of landfills. Therefore, the rest is trapped in the landfill and they are okay with that. I’m not. Next, there is the lifespan of the bulb. 8,000 hours is reasonable for a light that is left on 24/7. For lights in a typical home, 1,000 hours is more accurate. Their report shows the incandescent uses 5.8 mg from the power plants and the fluorescent uses 1.2. So the incandescent uses 4.8 times more power? Further, the report is trying to convey pollution per lumens, so this calls for “the CFL brightness adjustment”. My math says 16.4 CFL bulbs with 4 mg each of mercury plus 3.0 mg of pollution from coal. That makes CFL come in at about 68.6 mg of mercury pollution. 11.8 times dirtier than incandescent. And that’s just for mercury toxicity – there may be other toxins in CFLs.

    Concern 2: Instead of justifying toxic light bulbs with information about how toxic power generation is, I propose we use the non-toxic light bulbs and work on cleaning up our pollution generating power plants. Until the power plants are cleaned up, we can focus on other ways of saving electricity that are far more effective (later in this article).

More on CFL toxicity in the forum thread CFL Toxicity.

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