Light

Light

Full Moon

Although the full moon may look bright, it is thousands of times dimmer than the sun. All of the colors are still there, but we perceive a shift to blue for low illumination levels.

In case you haven’t noticed, or you have been an hour late all week, we are now in ‘Daylight Saving Time’. Now what is this light stuff and how do we ‘save’ it? I guess I must have been absent when the science teacher explained some of the information about light, but it must have been important, because 2015 is the ‘International Year of Light & Light Based Technologies’.

Light makes stuff visible to us. It wasn’t until the golden ago of Arab science that Ibn al-Haytham (965 AD-1040 AD) figured this out. Previous to that some complicated emanations from our eyes were believed responsible for our visual comprehension of things. Many years later it was determined that light consisted of electromagnetic waves, and the visual spectrum was from about 390 nanometers (nm) to about 700 nm. The smaller numbers tend to the ultra violet (UV) and the larger numbers tend to the infrared (IR). The UV gets you a tan, vitamin D, and skin cancer, so a careful balance is necessary.

The sun, our primary source of light, although it was hidden most of February, puts out light that is white with a blue sky background, even though the intensity is biased towards the UV. Sunlight is filtered through the atmosphere before it gets to us here on the ground. It’s interesting that water vapor is very transparent to the red portion of sunlight, and that is why ‘Red sky in the morning…’ indicates high humidity at dawn, so a possible shower is forthcoming. Conversely, water in its liquid form results in high attenuation of the red spectrum. A diver in crystal clear water loses most red light in a couple of fathoms, and I’ve always wondered why colorful critters evolved down there.

The visual spectrum holds roughly for most critters, although quite a few birds and insects have visual acuity that extends into the UV. Plants have evolved to thrive in the sun’s spectrum, and while experimentation indicates different values for different spectrum artificial lights, full spectrum fluorescents generally seem to be the lamps of choice.

The other important thing that light does is to affect the Circadian Rhythm of us and almost every other living thing. Our circadian rhythm is driven by our biological clock which has evolved to about a 24 hour cycle.  Generally this tells us when it’s time to be alert and time to relax, that is, be alert during the day and watch out for lions and bears that might be dangerous, and relax and sleep during the night. This happens to us when we are exposed to blue light, and this band of light controls the amount of melatonin produced, which apparently not only influences the sleep/wake cycles but also other bodily functions associated with SAD, diabetes, obesity, depression and cancer.

Other critters are also affected by light. The ratio of light to darkness apparently triggers snowshoe hares and weasels to change from winter garb to summer styles, and back in the fall. Some scientists suspect romance and migration in many birds are involved with light, although the migrations of our robins seem to be mostly influenced by temperature.

So I still don’t know how Daylight Saving Time is supposed to work, but if it adversely affects my circadian rhythm, I’m opposed to it. I don’t want to change the clock in my downeast Ford F150, and at my age I don’t want to learn how. Fortunately, the critters that I like to watch pay no attention to that nonsense. Maybe in the International Year of Light the politicians will see the light and abolish Daylight Saving Time.

Comments

  1. Around the equinox the length of day is changing most dramatically. Right now we’re gaining about 3 minutes and 10 seconds more sunlight every day here in Maine. That means an hour extra light in roughly three weeks.

    By contrast at the solstice the daylight changes by only a second.

    • Fred Gralenski says:

      Hi Mike
      Remembering my old mathematics(I think) the length of daylight is a sine function T=24/2[Sine 2(PI) ft].The derivative of this gives the slope or change. At the equinox the rate of change is a max, and at solstice it is zero.
      Cheers,
      Fred

  2. Joan Farnsworth says:

    Hi Fred,
    Nice column as usual. It is nice to have someone providing detailed information about the natural world.
    After wondering about the “why” of colorful critters in the ocean depths what have you come up with for an answer? Also is there colorful life in the underground waterways that get explored?
    Joan

    • Fred Gralenski says:

      I’m not sure why the colors of critters in the ocean depths. If the colors have no use, either camouflage or attracting mates, they can vary all over the place. Caterpillars need camouflage except when they are toxic, so the toxic ones can be colorful. I have never found much color in deeper lakes that I have dived in. Saltwater seems to have much more life in it.
      Cheers,
      Fred