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For the Same Reason It Shows Red, the Sky is Blue. And the Color of Energy?

Oddly enough the setting sun shows red for the same reason the sky is blue.  And to understand why that is the case, we need to step back and learn a few things – first about light, and then about the Earth’s atmosphere. And how both light and atmosphere interact with each other, and how the colors red and blue might better inform us about the use of energy.

Visible Light

Visible light is a very small part of the electromagnetic spectrum that ranges from the longer wavelengths of the infrared, microwave, and radio waves to the shorter ultraviolet, x-ray and gamma rays. These are all a form of energy that travels in waves.  What we call visible light is the incredibly small part (about one thousandth of one percent) of the full electromagnetic spectrum that our eyes can see.  And while light from the sun (or from other sources as from a light bulb) may look white, it is actually a combination of many colors that blend into white light.

At one end of the spectrum white light includes the reds and oranges. They gradually shade into yellow and green, and finally into blue, indigo and violet.  Each color has a different wave length and different frequency of that wave.  Within visible light, the reds have the longest wavelength but the lowest frequency and energy.  Violet light has the shortest wavelength but also the lowest frequency and energy level.

As long as nothing disturbs it, light travels in a straight line.  But as it moves through our atmosphere the light bumps into a gas molecule or a bit of dust. And here we next we learn something about our atmosphere.

The Atmosphere

What we call the atmosphere is actually a mixture of gas molecules and other materials that surround the earth. Compared to the size of the earth it is a paper thin composition that is mostly made of the gases nitrogen (78%), and oxygen (21%). Argon gas and water (in the form of vapor, droplets and ice crystals) are the next most common things. There are also small amounts of other gases, including the heat-trapping carbon dioxide emissions. And there are many small solid particles or aerosols like dust, soot and ashes, pollen, and salt from the oceans.

The composition of the atmosphere depends on location, the weather, and many other things. There may be more water in the air after a rainstorm, or near the ocean. Volcanoes can put large amounts of dust particles high into the atmosphere. Pollution can add different gases or dust and soot. The atmosphere is densest near the Earth itself. It gradually thins out as we move higher up. There is no sharp break between the atmosphere and space.

The Interaction of Light and Atmosphere

Light travels through space in a straight line – as long as nothing disturbs it. As it moves through the atmosphere, however, it bumps into many bits of dust and the many gas molecules. What then happens depends on the wave lengths of the light and the size of the things they hit.

Water droplets, dust and pollution particles are larger than the wavelength of visible light. When light hits these large particles, it gets bounced off into different directions. The different colors of light are all reflected by the particle in the same way. The reflected light, as in a fog, appears more white because it still contains all of the same colors.

The gas molecules of what we call air, however, are smaller than the wavelength of visible light. If light bumps into those molecules, it acts differently in a process that is called Rayleigh scattering (named after English physicist Lord John Rayleigh who first described it in the 1870′s). Some of it may get absorbed. After awhile, the molecule radiates (releases, or gives off) the light in a different direction. The color that is radiated is the same color that was absorbed. The different colors of light are affected differently. All of the colors can be absorbed. But the higher frequencies (blues) are absorbed more often than the lower frequencies (reds).

Why is the Sky Blue?

So the blue color of the sky is the result of Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air – especially at shorter distances of looking overhead when the sun is higher in the sky.  However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction we look, some of this scattered blue light reaches us. Since we see the blue light from everywhere overhead, the sky looks blue – intensely blue at times.

And Why is the Sunset Red?

As the sun begins to set, the light must travel farther through the atmosphere before it gets to us. More of the light is reflected and scattered. As less reaches us directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches our eyes.

As we look closer to the horizon, the sky appears much paler in color. To reach us, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches our eyes. The color of the sky near the horizon appears paler or white.

As we approach the evening hours and the setting sun, the sky and the sun may take on an array of colors. The most spectacular colors occur when the air contains many small particles of dust, pollution, or water. These particles reflect light in all directions. Then, as some of the light heads towards us, different amounts of the shorter wavelength colors are scattered out. As we begin to see the longer wavelengths,

The Color of Energy?

Like everything in the material world, and even within a spiritual context, ideas and things seem different as we shift our thinking, or perspective – or even as we choose what we want to observe.  So as the color of the sky, in a very analogous way we can think of energy as both the color blue and red.  As the color blue it primes the economy, but as the color red it also constrains it.

As the color blue, energy is an absolute requirement for the existence of all things.  Without blue energy in the form of calories to fuel our bodies, for example, we would be inert lumps of matter.  Yet, if we throw too much red energy into the biological process or our ecosystem, we generate a very large amount of waste.  One might say the ecosystem, and the smaller economy within, will overheat.  Building on the work of my colleagues Bob Ayres, my latest analysis – comparing the blue energy that is needed with the red energy that is wasted – suggests our economy is perhaps only 14 percent energy efficient.

I comment more about huge array of squandered resources in an earlier post, More by Waste than Ingenuity.  And about the impact this huge waste has on our economy, Shedding Leaves and Jobs.

At the same time, in our most indiscriminate ways, we tend to look only at the color blue when we think about energy.  Whatever efforts we then muster to try and manage the massive levels of waste tends to happen only after we’ve shoved billions of tons of energy through the economic process. If we brought the full range of energy colors into perspective we might focus, instead, on doubling, tripling, or quadrupling our 14 percent level of energy (in)efficiency.

The good news is that my ACEEE colleagues and I released a recent report just last month, The Long-Term Energy Efficiency Potential: What the Evidence Suggests,” that shows how we might slash energy use by 40 to 60%‒through highly cost-effective efficiency investments. This could, in turn, could generate up to 2 million jobs while saving all residential and business consumers a net $400 billion per year, or the equivalent of about $2,600 per household annually.

And what, we ask, might be the really colorful insight from this study? Instead thinking about tiny increments of improvement – even as we think mostly the color blue, the U.S. would be better off “Thinking Big” about energy efficiency and energy productivity. In effect, we would be much better off thinking about the colors red and blue together.

John A. “Skip” Laitner is Director of Economic and Social Analysis for the American Council for an Energy-Efficient Economy (ACEEE), based in Washington, DC.  Tucson is his family’s hometown, and he likely will be there through August of 2012. He hopes to provide a new posting roughly every week over the year.  While these columns do not reflect the official opinion or views of ACEEE, its board or its staff, he can be reached at [email protected].