The Reality-Based Community

Wal-Mart’s push to sell lots of compact fluorescent lamps (CFLs), on which I opined last week, has generated a post from Jane Galt (with lots of comments) and an article in today’s Times by William Hamilton. Together, these comprise the damndest fruitcake of conjecture, urban legend, assertive bloviating, and some useful facts in my recent experience. (Jane was woofing at the original version of this post while I was revising this.)

Galt’s basic point is that fluorescent light is depressing, so there. Curiously, people in the gloomy northwest with seasonal affective depression treat the condition with a big fluorescent fixture to sit in front of over coffee in the morning. Hamilton says the lamps aren’t hot, so they fail to tickle a primal something-or-other going back to the fire in a cave, and that the physical form of the lamps, a helical white glass tube, is intimidating. God help him if he goes near the New York Guggenheim, or comes upon a snail. Before I go on, I wish to record my absolute commitment to Galt’s and Hamilton’s and anyone else’s perfect right to buy all the electricity they want to run all the incandescent or any other kind of light they choose for no better reason than that they want to, or they just don’t like twisty shapes, or that they don’t like thinking about a fluorescent in that fixture even if they can’t see it and even if (as is demonstrably the case, according to one of Hamilton's sources) they can’t tell what kind of lamp is in it without peeking into the shade. Both these authors, however, have some recorded claim that their opinions might change if they learned something, and I assume this is true of readers of this blog. What follows is an attempt to describe the issues affecting fluorescent substitution for incandescent lighting with some facts; if you think I’m telling you what kind of lamps to buy, review the italicized text above.

The easiest issue to cover is brightness: if a 15w CFL doesn’t seem as bright as the 60W incandescent it is recommended to replace, just use an 18W; you’ll still save almost half a cent every hour it's on. (Watts measure the actual energy consumed by a device, what you pay for and (more or less) how much you're aggravating global warming; to compare light production, you have to look at lumens. The whole point of CFLs is that they produce more lumens with the a given wattage than incandescents.)

The naïve rap on fluorescents of any kind involves language like “harsh”, “flat” and “cold”. The first two of these can mean almost anything, but if it doesn't mean "too bright", harsh lighting usually describes light coming from physically small sources, that cast sharp shadows and make scenes with three-dimensional shapes very contrasty. Lampshades and more elaborate luminaires (luminaire is the technical name for a lighting fixture) are usually designed to enlarge the source of light from the lamps inside them, sometimes bouncing it off a big piece of ceiling, to soften shadow edges and reduce the contrast between lit and shadowed parts of our field of view.

Flat lighting usually means lighting that comes from such a large bright surface that there are almost no shadows or differences in intensity in the scene. Industrial and retail lighting from long fluorescent tubes has this property. Groovy hip retail establishments, and your living room, are usually lit to avoid this effect, with contrasty pools of accent light, but without the harshness a bare bulb would create. The most important advance in fluorescent lighting for home use is the physical reduction of the light source from the long familiar tubes to a compact shape almost exactly the size and luminosity of a frosted incandescent lamp; the second is the reduction of the large, heavy transformer (called a ballast) needed for traditional fluorescents (it’s about the size and weight of a brick, hidden in the luminaire) to something small enough to fit in the screw-in lamp itself. A CFL has exactly the same flat/harsh qualities as a frosted incandescent in the same luminaire, period.

What else might be bothering people? Color: fluorescents are different. Unfortunately the difference between fluorescent and incandescent is not as simple as it should be, so here goes. Anything that gets hot radiates energy in a band of wavelengths whose graph looks something like a rounded hat; as it gets hotter, it radiates more and the radiation moves to shorter and shorter wavelengths. Here are some color spectra, from a merchant's web site. An incandescent lamp filament is so hot that a lot of its radiation is in the narrow range of frequencies we can see, visible light, of which longer waves are red and shorter ones are blue. Operating cooler, the lamp gives relatively reddish light; make the filament a little shorter and it gets hotter and the light more intense and bluer – but the lamp burns out faster. Color ‘red/blueness’ is described by the temperature (in absolute degrees Kelvin) of a black object that would produce light of the color observed, called color temperature; for example, incandescents are made to trade off brightness (and efficiency) against longevity: A-type photoflood lamps, now rarely used, were 3400K (somewhat blue) and burned out in about four hours; ordinary household lamps are about 2800K, and so-called 130 volt incandescents are about 2500K but last a long time (good for inaccessible luminaires). Shadows on a sunny day (lit by sky only) can be 7000K; sunlight (photographic ‘daylight’) is about 5500, much bluer than almost any artificial light. Confusion alert: when we speak of cooler light, we usually mean bluer, even though this is the light radiated by a physically hotter object.

A fluorescent operates in a completely different way. The electric current running through the tube excites a gas (mercury - this is why fluorescents shouldn’t go in landfills) so that it radiates ultraviolet light (wavelengths too short to see, but able to give you a sunburn). The inside of the tube is coated with phosphors that reradiate visible light when they absorb the ultraviolet light, and people stay up late nights making phosphor recipes that radiate different mixtures of light wavelengths. However, each chemical radiates only a very specific wavelength, so even with a phosphor mix, the light from a fluorescent looks more like the teeth of a comb than the nice smooth shape from a hot object. Most wavelengths in visible light are barely there in fluorescent light.

One might well think this would make everything look really weird; with red and green but no orange wavelength, shouldn't an orange look black in between a tomato and a lettuce? But color vision doesn’t work that way: you can see a full-color scene, lettuce, orange, tomato, and all, with only two spikes of wavelength, and they can be yellowish green and greenish yellow! (What you learned about red, green and blue cones in high school is almost entirely incorrect; the truth is much more interesting and more complicated, and involves not only your eyes but your brain. The reason photography is so much fussier than we are about actual color temperature is because a camera doesn't have a real brain, just an eye.) A nice approachable discussion of this is here; if you want to get into it, search on retinex theory. Vision cannot distinguish the orange sensation created by an actual orange wavelength from the orange sensation created by a mix of red and yellow, nor, in a visual field with many colors, from the orange sensation created by a particular mix of the short and long wavelengths illuminating it, whatever they are! This is why an apple doesn’t look like a plum when you take it from your house (3000K) to outdoors (5500K +), even though the light coming from it to your eye is then much bluer, and why you can't tell whether a luminaire has a good CFL or an incandescent lamp in it. It's also one important way vision differs from hearing: two different pure sound wavelengths, say middle C and the G above it, sound like a chord and not like the E halfway between them.

However, subtle differences in color perception, not just "this is red and this is orange" but the sort of thing artists and photographers need to get exactly right, result from changes in illumination. Worse, some pigments display this effect more than others; Epson had to replace a whole line of otherwise excellent high-end printers and the inks they used because of the so-called metamerism that made photos seem to change color whan carried near a window. This photographer, though he gets retinex vision wrong, says that critical print viewing demands fluorescent llumination because incandescents will always be too warm. [Thanks to Mark, who used to work for Edwin Land, pioneer of the retinex theory, for making me improve this section].

Well-made fluorescents can have almost any color temperature (overall warmness/redness) we want, though this is achieved, again, with a mix of specific wavelengths and not a complete assortment of every color. (LEDs, the coming thing, have the same quality of unavoidably spiky frequency spectra, by the way.) The warmer the color, however, the less efficient the lamp, so manufacturers push the color temperature closer to daylight than incandescent is, just as they push the temperature down for incandescents to get longer lamp life. I put a variety of lamps in a Luxo and pointed them at a color temperature meter, something you should be able to borrow from a serious photographer if you want to play around; here’s what I found:

Halogen photoflood, 500 watt incandescent, 3160K (almost exactly what it should be. PG&E; may be delivering voltage just a tidge below 120 this evening, or someone is using the toaster on the same circuit; voltage changes incandescent color temperature a lot)
200 watt incandescent frosted: 2760K
Halogen incandescent reflector spot: 2670K
Greenlite brand 18W CFL: 3480K
GE dimmable 27W CFL: 3640K
Greenlite brand 15W CFL reflector flood: 3550K
Ceiling fluorescent luminaire, two 40W tubes, one cool white and the other warm white: 4600K

Note that the consumer incandescents are much further from the “standard” incandescent (the photoflood) than the CFL’s are (in the other direction). There’s plenty of variation in the “warmth” of light from incandescents already, and it’s interesting that people rarely complain about it; for example, if you dim an incandescent, it gets much warmer in color. The measurement of lighting color that takes off points for spikiness in the spectrum is called the color rendering index, or CRI. One way to improve the result of using fluorescents of any kind is to hold out for lamps with a CRI close to 100; still, there's a lot we don't know about the psychophysics of vision and individual responses may vary across people.

Two remaining issues are that CFLs usually take a minute or so to reach full brightness, which may vex some people, and that fluorescents used to flicker at 60 cycles, which a few people can see (and it drives them nuts; it’s also a hazard around machinery because the flicker can stroboscopically make things like saw blades appear to be standing still when they’re spinning). This is not a problem with modern fluorescents with electronic ballasts.

Finally, all of our perceptions, including strongly held ones, are profoundly influenced by set and setting; Coca-cola famously loses blind taste tests to Pepsi in one-sip quantities even though most grownups are happier with a whole glass of the former than the latter. People who will swear up and down that they have a favorite single-malt scotch that is much better than any other can almost never pick it out in a blind test (try it, if you don't mind making your friends angry). Lots of products create more or less real value for users than technically indistinguishable ones purely because of the associations glued to them by advertising and your social group's word-of-mouth. If you're like Jane, green at heart but sure that CFLs are really awful, try these experiments: First, substitute one lamp in a two-lamp luminaire or one of two luminaires; half a loaf is fully half a loaf, and you might be perfectly happy with the result. Second, when you go in someone else's house, pay specific attention to the quality of the light, make a judgment, and then look in the luminaires to see what kind of lamps they have. Third, ask a friend to sneak the odd high-CRI CFL into some of your luminaires and not tell you. You may be quite surprised about what you think you think, and what you think you like.

I can think of no better way to sum up this discussion that with Calvin’s dad’s immortal explanation:

C: Dad, how come old photographs are always black and white? Didn't they
have color film back then?
D: Sure they did. In fact, those old photographs ARE in color. It's just the
WORLD was black and white then.

C: Really?
D: Yep. The world didn't turn color until sometime in the 1930s, and it was
pretty grainy color for a while, too.

C: That's really weird.
D: Well, truth is stranger than fiction.

C: But then why are old PAINTINGS in color?! If the world was black and
white, wouldn't artists have painted it that way?
D: Not necessarily. A lot of great artists were insane.

C: But... but how could they have painted in color anyway? Wouldn't their

paints have been shades of gray back then?
D: Of course, but they turned colors like everything else in the '30s.

C: So why didn't old black and white photos turn color too?
D: Because they were color pictures of black and white, remember?
(thanks, Bill Watterson)

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Thread: Energy and Environment