Blurry blue lights
November 22, 2007 5:16 AM   Subscribe

I can't focus on blue lights. Is this normal?

I can't focus on blue lights. You know the blue leds on your games console, of the blue twinkly LEDs they use for xmas decorations? I can't focus on them. At all. They're just blue splodges that are a bit brighter in the middle.

Red LEDs? No problems. Green ones? Depends on the shade. Other colours? All good. Solid (non-illuminated) colours are all good too.

Depending on if you answer "it's XYZ" or "yeah, everyone has that", I have two different questions...

If everyone has it, why does it happen? If it's just me, why does it happen to me? :)

Extras : no colour blindness, but I wear glasses with nikon anti reflective polycarb lenses.
posted by twine42 to Health & Fitness (18 answers total) 7 users marked this as a favorite
Grab a prism and play with it.

You'll notice that red bends very little, yellow more, and blue quite a bit by comparison. This refraction makes it harder to focus on something mostly because, I suspect, our eyes were designed to focus on a more yellow-green "peak" in white light. The glasses probably don't help you in that regard.

If you want to see something that is very hard to focus on, just look at a blacklight. Those high end purples edging up into the ultraviolet are quite diffuse to the eye. I'd love to see a blacklight LED; I imagine the effect would be maddening.
posted by adipocere at 5:41 AM on November 22, 2007

It's possible that if you were in a dark room, where the only light was the blue leds, you could focus on them. But when they're surrounded by other things that are well lit with a broader range of colors, then indeed the chromatic distortion described by adipocere will prevent you from focusing on the blue.
posted by Steven C. Den Beste at 6:09 AM on November 22, 2007

Hence the rational behind "Blue Blocker" sunglasses.
posted by cosmac at 6:13 AM on November 22, 2007

Make that "rationale"
posted by cosmac at 6:15 AM on November 22, 2007

Response by poster: So adipocere has is sorted for daytime, but not at night?

In a dark room, the blue light on my PS2 is blurry while the red LEDs on other electronics are pin sharp...
posted by twine42 at 6:18 AM on November 22, 2007

I can't focus on blue lights regardless of the ambient light level. This can be so distracting at concerts and other productions that I need to turn away or close my eyes when the lighting shifts to mostly or exclusively blue.
posted by mollweide at 6:23 AM on November 22, 2007

I remember reading, in an Iain Banks novel perhaps, that the black lightbulbs made the small amounts of fluoride in your eyes produce light, which is why they appear blurry.
posted by stereo at 6:57 AM on November 22, 2007

Why this happens can be explained by the fact that blue light has the highest energy in the visible spectrum, despite its reputation as cool, it's actually hot. This higher energy makes it harder to deflect, so it won't bend as much when passing through a lens. It is also true that where there's violet, there's likely to be some ultra violet. If you wear glasses, have a UV coating applied.
posted by StickyCarpet at 7:17 AM on November 22, 2007

Short wavelength (S) cone cells (i.e. those sensitive to blue light) are sparse in the fovea compared to M and L cones, so people are in general less able to perceive blue. I think the standard way to demonstrate this is to have a blue dot and a green dot and to move back until the blue dot disappears; the green dot should stay visible.
posted by parudox at 8:27 AM on November 22, 2007

We're physiologically set up to be bad at seeing blue things in high acuity. Our eyes have three types of cones (as opposed to rods) that are used for color vision. The type of cone that maximally receives light at the short end of the spectrum is sometimes called the blue cone. These cones are a very small part of the visual system. Only five percent of the total number of cones are blue cones, and there are NO blue cones in the central two degrees of the foveal pit, where all our high acuity spatial processing takes place.

Why is this so? The standard explanation points to chromatic aberration. Different wavelengths of light get bent to different extents when passing through air, so if you try to superimpose all these differently colored images on top of one another, you'll get a blurry image. It might make sense for high spatial acuity to just rely on a small range of wavelengths in order to avoid blurriness. So, there's a possible explanation for why we use only two cones for spatial color vision. (The medium and long wavelength cones respond to light wavelengths that are very similar, so they don't produce much aberration. They are evolutionarily closely related -- one is a slight mutation of the other. The short blue cone is way down the range.)

So, don't feel bad. We're all bad at seeing blue things! I find those deep blue LEDs that suddenly appeared all over the place a few Christmases ago to be totally hypnotic for this reason. Compared to all the other colors of lights, they just look so flat.
posted by painquale at 10:57 AM on November 22, 2007

You must have excellent vision. It's true that blue light focuses a little bit behind the retina, making things a little out of focus, but most people's visual acuity isn't good enough to be able to notice it.
posted by ikkyu2 at 11:16 AM on November 22, 2007

Ack. I meant that people are less able to detect blue, rather than to perceive it.
posted by parudox at 12:16 PM on November 22, 2007

I would bet a large amount of money on it being your lenses. I moved from my old pair of glasses, which were basically the "economy" pair, to a new pair with anti-glare, anti-reflection, anti-everything polycarb lenses and quickly noticed that blues were sometimes slightly out of focus, especially near the edges. And when I turn me head from side to side and stay focused on something blue, it noticeably "drifts" when compared to the rest of the room.

Neither of these occur with my old glasses or with my contacts.
posted by Benjy at 1:39 PM on November 22, 2007

First, facts:

Lenses focus different wavelengths of light at different distances. Consider an old camera lens; most have a red dot on one side of the focus-distance marking. That is the offset to use when using infrared film and capturing IR light only. One focuses using the visible (higher frequency) light, then one moves the focus ring that distance to get how it would focus at the typical "color" of light you're going to capture.

Okay, now you know you have two different kinds of photoreceptors in your eyes, yes? We typically call them "cones" and "rods". The rods see intensity or lightness/darkness of light, where the cones distinguish the colors.

Now, conjecture:

If you're trying to see something on the edge of your normal visual spectrum, then maybe these two kinds of cells disagree about how far away something is. Your normally automatic focusing gets a noise of signals from the cones and the rods, each saying "no, what I see is out of focus!" and your brain wigs out.

AFAIK, it's at least plausible.
posted by cmiller at 2:19 PM on November 22, 2007

Maybe it's because our eyes suck at blue.
posted by ulotrichous at 7:52 PM on November 22, 2007 [1 favorite]

How strange - I was out walking with my girlfriend last night and we were commenting on how it was just impossible to focus on the new blue LED lights some of the Police cars are sporting here. I then ended up noticing that I had trouble focusing on the really bright green LEDs that make up the "walk" symbols too.

Interesting to know other people were thinking (and answering) the same things at the same time! Thanks.
posted by benzo8 at 9:30 PM on November 22, 2007

I find those deep blue LEDs that suddenly appeared all over the place a few Christmases ago to be totally hypnotic for this reason.

A while back I asked this about the green LEDs, which has a good link to a Wired story about the history of the blue. Arigato, Nakamura-san, once again.
posted by Rash at 8:24 PM on November 23, 2007

Why this happens can be explained by the fact that blue light has the highest energy in the visible spectrum, despite its reputation as cool, it's actually hot. This higher energy makes it harder to deflect, so it won't bend as much when passing through a lens...
posted by StickyCarpet

Nope. It bends more.
posted by weapons-grade pandemonium at 8:37 PM on November 30, 2007

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