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Questions tagged [light]

Electromagnetic radiation, specifically the range of wavelengths visible to humans ("visible light").

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16
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6answers
19k views

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 ...
13
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1answer
673 views

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 ...
3
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1answer
787 views

What is the biological potential for vision of wavelengths outside the human visual range?

Humans eyes have evolved to perceive light only between approximately 350-700nm, because that form of light is most common to our lifes. Other animals can perceive lights with slightly different ...
20
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1answer
551 views

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 ...
9
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1answer
2k views

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 ...
5
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3answers
4k views

What does “chlorophyll photosynthesis peak” mean in relation to photon wavelength?

When reading about how green / leafy plants work, I saw that they have chlorophyll A & B, which allow the plant to use the energy from light by capturing and transforming. When reading about ...
13
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1answer
11k views

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 ...
16
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1answer
4k views

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 ...
7
votes
2answers
343 views

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". ...
5
votes
1answer
226 views

Can other animals see black differently?

I am not sure if this is the right place for this question, but this is a debate that has been going on between two colleagues for days and I need a resolution because it's driving me crazy. So any ...
11
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1answer
7k views

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 ...
10
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2answers
43k views

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 ...
14
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1answer
245 views

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 ...
8
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3answers
8k views

Photosystem 1 and 2; P680/P700; Chlorophyll a/b

I am getting slightly confused about how the above relate to each other. My current understanding is that P680 and P700 refer to the primary pigment reaction centres in Photosystems 2 and 1 ...
2
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0answers
64 views

Mobile carriers of Light reaction in higher plants

The hydrogen carrier PQ and the electron carrier PC are the mobile carriers in light reaction facilitating electron transfer from PS II to PS I during non-cyclic process. My question is - How do ...
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1answer
1k views

Is it safe to look indirectly at the Sun?

I.e., is exposure of sunlight onto the peripheral vision less damaging than exposure onto the fovea?