An answerer at Quora claims:

Colour vision is a result of cone cells. People with normal vision have 3 cone cell types: red, green blue. Of the 6-7million you have, 45% are green. Therefore, your eyes need to work less to perceive colour. Dark greens (pine tree green) are one of the most relaxing colours.

Answerers at AnswerBag have similar claims:

Green has great healing power. It is the most restful color for the human eye; it can improve vision.

Green is very restful to the eye and it's at the opposite end of the spectrum to red, which is also the most emotionally charged colour. So looking at green not gives your eyes a break, it calms you emotoinally.

None of these provide verifiable evidence.

This is distinct from the claim that looking outside might be good exercise for your eye muscles.

Does looking at the colour green relax your eyes more than other colours.

  • 1
    This is mixing two different claims - that the colour green is relaxing for your eyes and that looking at distant things is good eye exercise. I am going to edit to limit to the first claim, which is the only one referenced. – Oddthinking Aug 1 '13 at 10:13
  • I would guess that the advice to look out of the window is about changing your eyes' focal length (thereby exercising/resting the ciliary muscles) than looking at a particular colour. It just happens that there is usually green outside. – slim Aug 1 '13 at 10:16
  • @slim: Just changed the question to emphasize it is NOT about that - neither of the cited claims make that point. (The notability of this questions is still pretty weak. Is it more than a couple of randoms posting nonsense?) – Oddthinking Aug 1 '13 at 10:20
  • Thanks for the edit. This question was posted in good faith and no ill intent was intended. – Samuel Liew Aug 1 '13 at 10:29
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    I'm referring to the eyes. If I wanted to relax the mind, there are better ways to do so. – Samuel Liew Aug 1 '13 at 13:58
up vote 11 down vote accepted

The claim at Quora is close to the mark, although not exactly for the reason claimed. All lenses (including our eyes) suffer from chromatic aberration, a kind of distortion that occurs because different colors have different refractive indexes. In photographs, this distortion results in fringes of color in high-contrast areas. In eyesight, it can increase the difficulty of focusing on certain colors and color combinations.

The textbook Basic Sciences for Opthalmology (Bye, Modi, Stanford, 2013) relates this to the construction and mechanics of the eye:

Chromatic aberration in the eye

In the eye, the dioptric difference between the dispersion of red versus blue light is approximately 2D (Fig. 8.23). Remembering that the human eye's peak spectral sensitivity lies at 550 nm (green), the human retina is deliberately placed such that it is in between the dispersion of white light, i.e., between red and blue. This optimizes the best level of focus specifically for its peak spectral sensitivity. The pupil and the nucleus of the lens also help to minimize chromatic aberration.

In short, the eye is constructed such that it is easiest to focus on green light, which is in the middle of the visible spectrum and has the strongest receptors. Normally, blue light focuses slightly in front of the retina, red light slightly behind. When red and blue patterns are mixed in an image, this chromatic aberration can create an illusion of depth called chromosteropsis (Dictionary of Optometry and Visual Science, Millodot, 2009). In extreme cases, it can cause eyestrain as the eye shifts rapidly in an attempt to focus on the red and blue light at the same time.

There are a couple of other effects that may contribute to the perception that green is a less strenuous color, one physical and one psychological. Blue objects are less visually distinct than red and green, partly because of chromatic aberration, but also because blue cones are located outside the fovea, the best-focused part of the retina with the best resolution (paraphrased from Optics, Hecht, 1987). Meanwhile, the color red signals dominance, aggression, and danger psychologically. While this does make red objects easier to spot, the emotional loading may cause nervous system arousal and stress. (This is a widely-held belief, alluded to in the AnswerBag post, but I should note that it's disputed in a 2004 paper by Robinson, and I don't have the necessary background to evaluate it.)

  • Meanwhile, the color red signals dominance, aggression, and danger psychologically -- I watched a TV documentary about the effect that plant-life has had on the evolution of Planet Earth: it said that the reason why we (humans) have color vision is so that we can distinguish between ripe and unripe fruit (ripe fruit being red as opposed to green). There's a similar allegation at en.wikipedia.org/wiki/Color_vision#Evolution – ChrisW Aug 2 '13 at 17:49
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    Yes, I saw that claim at Wikipedia too. Couldn't find a better source though, and I didn't want to muddy the waters further on the claim, so I stuck to the elements that are widely believed. The Robinson paper confirms that it's conventional wisdom, although it's in the context of trying to debunk it. (The psychological effect of red color might make a good question of its own.) – Bradd Szonye Aug 2 '13 at 17:55

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