General Question

6rant6's avatar

How much of the energy the earth gets from the sun is in the visible spectrum?

Asked by 6rant6 (13604 points ) August 30th, 2012

The sun shines. Things here get hot. Black things reflect less energy than white things (or mirrors) and so get hotter. How much of the sun’s energy that the earth absorbs at ground level is in the visible spectrum?

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10 Answers

PhiNotPi's avatar

Here is one chart that I have found. It does not cover the entire spectrum, but it shows that a lot of visible light is received compared to other ranges of light (the height of the graph). Even if this is the case, it is still possible for the total amount of nonvisible light to vastly outweigh the amount of visible light, since the vast majority of the spectrum is not visible (the width of the graph).

gasman's avatar

According to Wikipedia …roughly 44% of sunlight energy that reaches the ground is visible [7]. (Ref. 7: Reference Solar Spectral Irradiance)

This high figure should not be surprising, because the sun’s spectrum peaks in the visible – which in turn is no coincidence given the long evolution of vision.

PhiNotPi's avatar

It’s weird how I can’t find the above information on the article about “sunlight” (unless I’m just blind).

6rant6's avatar

@PhiNotPi I saw it. It’s there.

gasman's avatar

@PhiNotPi It’s under “Light Sources.”

Bill1939's avatar

As @PhiNotPi‘s chart shows, a significant portion of the spectrum’s energy exists in the visible wave lengths. However, wouldn’t heat be produced by wave lengths below red? Looking at the chart, the sum of the area between wave lengths750 nanometers and 2500 nanometers seems close to the sum of the visible wave lengths.

PhiNotPi's avatar

I still don’t see it. I was talking about the article about “sunlight,” not the one about “light” (although I did find it on the one about light). But it’s not that important.

gasman's avatar

@Bill1939 The irradiance chart measures watts per square meter, i.e., total energy flux. Your point is well taken that radiant energy represents more than just heat. Visible light energy, for instance, is what plants use to convert CO2 into stored sugars. Ultraviolet energy is what tears up the DNA molecules in our skin, etc. Some non-infrared photons still contribute to heating, however, though I’m not sure how to estimate that.

augustlan's avatar

[mod says] This is our Question of the Day!

Crashsequence2012's avatar

Not enough information given in original question:

Visible by what?

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