Questions tagged [light]

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

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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 ...
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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 ...
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 ...
15
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2answers
2k views

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 ...
14
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1answer
244 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 ...
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 ...
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 ...
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 ...
11
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1answer
2k views

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 ...
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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 ...
10
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2answers
202 views

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 ...
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 ...
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2answers
8k views

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 ...
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 ...
7
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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". ...
7
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1answer
464 views

Why are we able to differentiate between colored objects without the presence of light?

Rods help us to see during the dark. We can see colour of the object when it reflects light. But in a dark room(room of any color but the light is switched off and it is night),we still can ...
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0answers
89 views

Why do we fear the night? [duplicate]

I always feel more afraid in the dark than in light conditions. Is this a common phenomenon in all the people? Does it have biological underpinnings?
6
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1answer
277 views

Receptors for red and far-red light in plants: Shade avoidance

Franklin (2009) describes how plants use the ratio of the red wavelength (660-670nm) over the far-red wavelength (725-735nm) (R:FR) in order to avoid shading. My question is: which receptor is ...
6
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2answers
16k views

Does bright environment strain eyes more than dim?

I'm trying to figure out how to modify my working conditions so that I can program longer without harming my eyes. Because doing so experimentally hasn't given conclusive results so far, I decided to ...
6
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1answer
256 views

Question to the color scientists

I have a question. if you look at these two spectral diagrams (SPDs) from two different televisions that is calibrated to the same white point (D65) 6500K with a spectrometer. The problem is that ...
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 ...
5
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1answer
550 views

What kinds of light attract moths best?

On average, do we know what kind of lights attract moths best? LED, filament bulb, candle...? And what about colour? Does that matter?
5
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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 ...
5
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0answers
163 views

Where can I get numerical data for the PAR (photosynthetically active radiation) curve?

I'm trying to do some rough figuring to calculating efficiencies of various light sources for growing plants. I'm hampered, however, by the lack of a curve to multiply by the spectrum of light ...
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2answers
1k views

Why do most plants reflect green and others other colors?

I have read that chlorophyll absorbs red and blue. As shown in detail in the absorption spectra, chlorophyll absorbs light in the red (long wavelength) and the blue (short wavelength) regions of ...
4
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1answer
250 views

What is blue light?

What is the "blue light" often discussed in relation to human melatonin production, sleep/wake cycles, etc.? A Google search seems to define it as light of a particular wavelength, suggesting that it ...
4
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2answers
342 views

What causes a selective shift of colour perception after removing wavelength filtered glasses?

Background To improve sleep by reducing blue-light melatonin disruption, I wear night-glasses that filter short wavelengths (e.g. something like these). With these glasses on, both the top and bottom ...
4
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1answer
3k views

Are insects attracted to near infrared light?

Do insects see near infrared light? If yes, are they attracted to it at night, as they are to visible light sources? I am building something similar to a home-made trailcam with a Raspberry Pi ...
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 ...
3
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1answer
148 views

How are chickens affected by light?

When I was young, I was told never to put a fluorescent light in a hen house because it continuously turns on and off. Extra lighting is used, as far as I know, to 'extend' a chicken's day. Human eyes ...
3
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1answer
111 views

Why is flash light harmful to what aquatic life forms?

When visiting an aquarium, it's often not allowed to take photographs with a flashlight on. It is said that the flash light with very high intensity is harmful to the displayed life forms. I respect ...
3
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1answer
819 views

Any examples of animal behavior in response to meteor showers?

I just spent two nights observing the Perseids and was wondering whether any animals have been recorded to exhibit unusual behaviour in response to meteor showers. It is known that some animals ...
3
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0answers
92 views

Can low melatonin levels and/or LED lights cause or exacerbate macular degeneration?

I have two questions that may or may not be interconnected. My first question is: Does melatonin prevent macular degeneration? Could low melatonin levels (caused by blue-rich light exposure in the ...
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0answers
69 views

What amount of light energy is required to produce one O2 molecule? How about one molecule of NADPH?

I know that for each O2 molecule, a total of 8 photons are required (4 per photosystem). Would the amount of light energy required be E=hc/wavelength using 680 and 700? Or would the energy from the ...
3
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0answers
7k views

Why do I see the world in blue when I open my eyes? [closed]

So I was standing outside, waiting for the train. I was tired so I closed my eyes for a while. Then when I opened them, the world was a lot more blue than it normally is - why is this? I tried it a ...
2
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2answers
588 views

Can the retina emit light?

The retina is light sensor, which converts light to an electrical signal. LEDs can both emit and receive light. Similarly, is it possible to apply electricity to retina to generate light? Simply put,...
2
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1answer
275 views

Can microorganisms (e.g. bacteria) be damaged or killed by 253,7 nm light?

The question arose in a hospital, where I saw these flyers advertising lamps that emit such light. It was claimed that they can clean the air of microorganisms up to an arbitrary degree. Does anyone ...
2
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1answer
879 views

What is the chemical process involved in human hairs changing colour after sun exposure?

After a day at the beach, my skin tans due to Melanin. But I also observe the black hairs on my arm turn a blond colour. My question is What is the chemical process involved in human hairs ...
2
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1answer
265 views

What photoreceptors are necessary to permit infrared vision?

Humans have red green and blue photoreceptors allowing them to sense colours in the spectrum of about 400-700nm. Certain proteins allow for the extending of wavelength range in the RGB receptors, this ...
2
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1answer
110 views

Using UV to kill bacteria in shoes

I see that UV-C is the best to kill bacteria generally. We are interested in using to kill off odor in shoes. What illuminance is needed to kill most bacteria with UV-C? Thanks!
2
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1answer
2k views

Is light required for seed germination?

Is light required for germination of every seed? If not, why don't some plants require it? Is there any difference in the quality and duration of light required ? It would be interesting if someone ...
2
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1answer
51 views

Why does a lightsource postpone the time it takes for the leaves falling from a birch tree?

It is autumn and the leaves have already left their trees on all birch and other trees that has leaves, except one. This birch has a spotlight pointed to the tree and it is on 24/7. I have recognized ...
2
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0answers
52 views

What happens when pure chlorophyll A absorbs blue light?

When pure chlorophyll A is put in the presence of only blue light, what happens? My guess is that the extra energy is released as heat/kinetic energy, and then the electron has dropped to the lowest ...
2
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0answers
31 views

Are natural daylight lamps for Seasonal Affective Disorder just about the color temperature?

I've seen many expensive lamps made for people who have Seasonal Affective Disorder (SAD) and/or who live in regions where there isn't much daylight during the winter. I'm wondering if the benefit of ...
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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0answers
2k views

Does Rüppell's Griffon Vulture Have Greatest Vision Acuity? (Small Carrion Spotted at 10 km+?)

Synopsis: Some sources seem to imply the Rüppell's (griffon) vulture (Gyps rueppelli) can see objects at a distance in excess of 10 km -- roughly three times the ...
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0answers
62 views

What do I need to do to make a Reverse colorblind image?

As a 15 year suffering from moderate Protan colorblindness, I've wanted to find any advantages of colorblindness. I discovered there are Reverse colorblind tests, which only colorblind people are able ...
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0answers
119 views

What wavelengths of lights do plants need to grow?

So, I found a list of L.E.D.'s from Cree here (the company seems to be known for efficiency, they power most of the bicycle lights that I know of) is selling a line of lights designed for growing ...
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0answers
534 views

Is there a meaningful difference between direct and indirect light

I don't see a basis for a distinction, but I've heard several people distinguish between direct and indirect light for people, claiming that indirect light would be better in many cases. "Direct" ...
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0answers
17 views

Surface Power Density of Fluorescing Reaction

I am looking to find out what is the ballpark power density of a fluorescing PCR reaction using a SYBR Green or Taq Man dye might be. Is it on the order of $E_e=1mW/cm^2$, less or more? Any help of ...