Electromagnetic radiation, specifically the range of wavelengths visible to humans ("visible light").
Questions tagged [light]
108 questions
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Why are fearful stimuli more powerful at night?
For example, horror movies appear to be scarier when viewed at night than during broad day light.
Does light have any role in this phenomenon?
Are there changes in hormones at night versus during the day that makes fear stronger?
user237650
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Why is human vision restricted to 400-700 nm?
Across the electromagnetic spectrum, 400-700 nm is a narrow spectrum of frequencies and focused in the region of short wavelengths. For example, radio waves cover a large range of frequencies unexploited by the visual system. So what biological…
HyperLuminal
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Are two colors (red + blue) necessary for LED grow lights, or would either color be sufficient?
Below are some chlorophyll absorption spectra from other answers here. There is strong absorption at both the blue/violet end, and the red end of the spectrum, and presumably both of these contribute to steps in water splitting used in…
uhoh
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Why do dog's eyes glow green on a photo?
Taking my current profile picture as a prominent example:
This photo has been taken with flash. As I gather, this is the same effect that makes a human's eyes glow red on photos, namely the reflection of the flash at the choroid and then passing…
Vogel612
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Are there specific conditions that allow humans to see ultraviolet wavelengths
It is fairly common knowledge that the lens in its normal state absorbs ultraviolet (UV) radiation. An interesting notion has come up from time to time in my reading that suggests there are a small number of conditions that result in humans being…
user3795
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Can UV radiation be safe for the skin?
It is well known that UV radiation can damage the DNA and generally harm our skin.
We also know that UV radiation helps on the production of melanin and Vitamin D.
From what I could find, the DNA absorption spectrum goes to almost zero for…
cinico
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Can "red" cone cells actually see much red light?
In electronics, the most common color scheme is the "red-green-blue" (RGB) scheme. This choice is often justified by claiming that the long- (L), medium- (M), and short- (S) type cones in the human eye are most sensitive to red, green, and blue…
tparker
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Why do human eyes glow red on a photo and dog's eyes green?
Previous Research
I know that cameras sometimes come with an anti "red eye" functionality that involves two flashes, presumably the second flash coincides with the shutter opening.
Question
Why do camera flashes sometimes lead to photos of humans…
hello_there_andy
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Does your iris color have an effect on your vision?
I've always wondered if having different iris colors, (eye colors) may have any advantages or disadvantages on ones vision. Specifically regarding the effects of light.
Personally, I have troubles being out in the bright sun without sunglasses. My…
AstroMax
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Why can I see a light flicker when it's in my peripheral vision?
When I'm looking at an old CRT monitor or a worn fluorescent lamp, but not directly in the center of my gaze, the light from it seems to flicker. When I focus my gaze onto the monitor or lamp, the flickering stops.
Why can I see a light flicker only…
Marc Dingena
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Is it safe to look at infrared LEDs?
What happens if one looks directly at infrared LEDs? Sometimes I see this kind of LED at night as red dots and I'm also courious about it.
I was wondering what would happen if one looks directly to these LEDs, because we see them everywhere like in…
Vladimir
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Does artificial high intensity light damage permanently dark ecosystems?
Popular science features on wildlife typically capture camera images using natural light, or high-speed exposures. This is not possible where the ambient light is extremely poor.
E.g. Caves, Undersea
For beings accustomed to the stygian dark, the…
Everyone
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What is the minimum light intensity that a human eye can detect?
By doing a quick search in Google, I find a series of pages dedicated to physics exercises claiming that the human eye threshold for light intensity is $10^{-10}$ W/m${}^2$. However I cannot find any reference for such a value. Is it even the right…
Mauricio
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Cerebral activity during exposure to non - visible light
Our eyes only have the ability to sense light within a certain spectrum. My understanding is that particular frequencies energize specific cells in our eyes, each responsible for a different "color". When these cells are energized, they each release…
Jonathon Anderson
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Why do I still see a bright light after looking directly at it?
When you look directly at a bright light, maybe accidentally when looking at the sun, the shape of the image may persistently be perceived even after you look away.
Does this image persistence have something to do with the light hitting the back of…
Beastly Gerbil
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