MY FATHER ONCE worked as a project engineer, where he was in charge of the design and development of room temperature-regulation devices such as thermostats for home and commercial properties. He tells of a room, warmed with radiant ceiling and baseboard heaters: even though the air temperature would be 50° Fahrenheit (10° Celsius), it still
felt comfortable.
It seems that our natural perception of warmth and coolness is
not primarily determined by air temperature; rather, our senses may instead measure infrared radiation, that is, the portion of the
electromagnetic spectrum that is lower in frequency than red-colored light. Infrared is invisible to the eye, but still can be felt by the skin.
A few weeks back, I spent some time outside: it was a brilliant, clear day; the air temperature was about 25° F. (-4° C.), without wind, but I was completely comfortable without wearing a coat or hat. I did have to turn around a bit to warm up the various sides of my body, but clearly the radiant heat from the sun was sufficient for my comfort. Infrared photography confirms this: skies thus photographed are black and therefore are transparent to that kind of radiation from the sun. Likewise, campfires have long been used to keep people warm outdoors, even in very cold climates; even though the fires only warm the air above them, their tremendous infrared radiation is sufficient for human warmth.
Human skin and many garments are transparent to a wide range of infrared radiation, and the most important source of heat loss in humans is via the same radiation of infrared. (The other major mechanism of heat loss is sweat, and the presence of wind is often important). And so logic and physics tells us that the most efficient source of human heat gain is also infrared radiation.
A while back, I discussed this phenomenon with a physician friend of mine, who was also interested in this; he believed that it was insufficiently studied, and could be a fruitful area for future research. So, please allow me to offer some speculation on the subject of artificial heating and illumination.
For the sake of energy efficiency, we are told that we ought to replace wasteful incandescent lamps with efficient fluorescent bulbs. Governments have even started
banning or restricting incandescent light bulbs. This seems to make sense, for most of the radiant energy given off by the old light bulbs is invisible infrared radiation, and is therefore wasted.
Or is this energy really wasted? Please recall that this infrared radiation is perceived as warmth, in a very strong way, and may be far more important to the perception of warmth than air temperature. If a room is re-bulbed from incandescent to fluorescent lamps, how much warmer will the room's air temperature have to be to feel the same? Please note that this relationship probably still has not been thoroughly investigated. The room where I am typing this has two 60-watt incandescent bulbs in a ceiling fixture: I've noticed that when I have the lights on, I am able to keep the air temperature at least 5° F. cooler than when the light is off, and feel equally comfortable. If I were to replace these bulbs with compact fluorescent lamps, this temperature advantage would be lost. In the big picture, which is the most efficient? Would people tend to turn up the thermostat in fluorescent-lit rooms? (I ought to note that in the summertime, I rarely use either electric lighting or air conditioning.)
Of course, as always, turn off the lights as you leave the room. Didn't your mom tell you that?
I do use fluorescents in the lights I use for security, like my front porch, where electrical efficiency actually is important. I also enjoy 'light emitting diode' lamps for flashlights, where electrical efficiency is extremely important.
As I've gotten more serious about photography, I've noticed that fluorescent lighting is inferior in color quality compared to daylight and incandescent lamps. Fluorescent lights generally give off a sickly green color, quite evident in photos. And when fluorescent and incandescent lights are mixed in the same photo, the contrast between the relative green and magenta light given off by them produces a terrible-looking photograph. The same goes for natural daylight coming from the windows, which is also relatively magenta compared to fluorescent.
I find that my photos of church interiors are better if fluorescent lights are off. Incandescent lighting, daylight, or candlelight, is more beautiful.
The whole variation of natural lighting forms a harmonious range of color: from the very blue light in shade, to the white light of the sun high in the sky, down to yellow candlelight. Incandescent lights match this harmonious range of color from blue to yellow, and a mixture of these colors looks better in a photograph than does the green-to-magenta variation seen with fluorescent lighting. Although I typically correct a photo for the color of the light, the eye is tolerant of wide variations between this natural blue and yellow, and is biased towards accepting yellow. The eye strongly rejects a green/magenta light color variation in a photo, which looks just plainly bad. This natural range of the color of light is known scientifically as a '
black body spectrum', which typically includes a large amount of invisible infrared radiation, which we discussed earlier.
As bad as fluorescent lights are, even more efficient light sources, such as sodium vapor lamps, are even more awful when it comes to color quality. While there are plausibly good reasons for using these outdoors, I cannot think of any convincing reason to use them indoors.
Besides luminous ugliness, there are also health concerns regarding fluorescent lighting, which I will not go into here due to my ignorance.
These arguments in favor of incandescent lights also apply to candles, which deserve some discussion at some other time.
Incandescent lights still have their use, and ought to be thoughtfully reconsidered before being banned.
