Questions tagged [light]
Electromagnetic radiation, specifically the range of wavelengths visible to humans ("visible light").
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Image sensitivity of eyes and peripheral vision
I have bad eyes and need glasses. However I have noticed when it is dark, I am able to see contrasting colours a lot better in the corner of my eyes, than in the center, e.g a mark on my wall I can't ...
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Can both lenses of different eyes intentionally focus at different amounts
Can each lens of both eyes have different accommodation rates, or have a different focal length to view objects of different distances. I understand that this can be a problem known as Anisometropia, ...
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Can mammals and/or birds see / detect infra-red light?
Wondering if there is any evidence that mammals or birds eyes can detect light emitted in the infra-red? The reason I'm asking relates to the use of nest cameras to detect predators, using infra red ...
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How do we see the violet color?
Here is exactly the same question with an accepted answer. However, that answer looks wrong (I can’t find the “alert moderators” button). Firstly, it refers to a dubious source. Secondly, it ...
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Near-infrared EM spectrum and uses in biology (specifically in botany/vegetation)
A little explanation for my problem:
I have a large dataset - images of aerial scans of my country. These images are available in both RGB and RGBN colors - N specifying the near-infrared color ...
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Does sunlight interfere with the efficiency of compound light microscope?
I have access to an olympus bx41 microscope. The table on which sits the microscope is in front of a large window and unfortunately no curtains are available. I'm starting to relate that whenever the ...
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Do color-blind people have more rod cells in their retinae than the normally sighted?
All types of color-blindness are said to be caused by the defect or lack of cone cells in the eyes[1]. Since cone cells sense color[2] and rod cells can only sense light intensity[3], the lack of cone ...
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Why do flies and fruit flies exhibit two distinctive (but not exclusive) flying patterns?
I live near a forest with a canal, and often see fruit flies, they also sometimes come in our house and occasionally feed on bits of fruit. Also, sometimes I meet regular house flies here and there, ...
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Relation between image on retina and the real one: looking at the two objects that are 45 degrees apart, what's the distance in the actual image?
These are what I understand about the vision.
lights come through the pupil.
an inverted image of the real objects is formed on the retina. which is determined by the angles.
(so (a, d) and (b, c) ...
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Laser in mirror experiment
Apologies if this question is very simple I performed an experiment where I would shine my toy laser at the mirror and it would be reflected.
Now here is what I tried:
I could see my laser toy , I ...
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Did animals primarily evolve to differentiate UV-rich sky from UV-poor substrate OR did they evolve to see visible light? [duplicate]
I read two things that appear to contradict each other.
The reason humans only see light in the visible spectrum is likely related to the transmission of light waves through water: most infrared and ...
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Happiness from sunlight is from IR or UV?
I found this study that shows that UV light makes our skin release feel-good endorphins. This is the pop-sci writeup.
On the other hand, it seems like IR is what causes the sense of warmth in the skin ...
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Absorption bands of chlorophyll
I am currently reading this article, which discusses the functional impact of the $Q_x$ and $Q_y$ absorption bands of chlorophyll in photosynthesis. However, the article didn't say where on the ...
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Primary charge separation in Photosystem II
I was reading through an article about primary charge separation in Photosystem II when I came across the following graphic:
I assumed that the axis is measured with respect to the unexcited system, ...
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Why do humans see exactly one octave of light?
The visible spectrum of light is often defined as 350nm to 700nm. On Wikipedia, it says 380nm to 750nm. Either way, the upper bound is very close to double the lower bound. This means humans can see ...
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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 ...
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Why do people say that blue light is damaging to the eyes?
It's easy to find claims that blue light (e.g., from computer screens) is damaging to the eyes. For example, here is some discussion of the topic. Is there any physical mechanism by which blue (not ...
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How many photons does a GFP molecule absorb per second?
I'm trying to calculate how many photons will a GFP emit per second. The calculation seem easy just multiply the number of absorbed photons by the quantum yield. But how can I obtain the number of ...
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What happens to plants if they are exposed to "sunlight" 24h a day?
I just wondered if one could grow plants faster, if they were exposed to sunlight-like light all the time.
In a similar question which is not the same, I could confirm that plants have different ...
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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 ...
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Can insects be killed by intense visible light?
Some mosquitoes and flies were sitting on the white ceiling. I took a very powerful flashlight to try and daze and then vacuum them.
When I put the flashlight's head against the ceiling (with a ...
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How is the extraordinary eyesight of some deep-sea creatures explained?
Mantis shrimp is a marine crustacean that is known to have a vision system that is much more complex than the eyes of many animals living on the ground. As explained here, it has 12 types of ...
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What is the true response of human photoreceptors to different wavelengths? Why is there so much disagreement in the literature?
I can find several qualitatively different diagrams of the responsiveness of human cones and rods to different wavelengths of light.
A page referencing Bowmaker and Dartnall, 1980 has the following ...
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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 ...
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Fluorescent purple flowers?
Do some flowers fluoresce? Some deep purple Lobelias and larkspurs seem to glow and confuse my eyes in sunlight. It reminds me of those blue LED Christmas lights (they come in strings with other ...
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Would green light look different if blue and red cones were deactivated
When looking at a graph plotting "blue", "green" and "red" cones reponses to different wavelengths, you can see that any wavelength trigerring a response from green cones ...
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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 ...
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Why when measuring turbidity do we use the minimum wavelength?
As a preface, I read a few other related posts and was able to gather some knowledge, though without any background in physics I am having some trouble here piecing together a coherent view. I looked ...
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Most optically transparent muscle phantom?
I am trying to use Schlieren imaging techniques to visualize how a sound wave propagates through muscle tissue.
In the past, when needing to experiment with muscle we would use an agar based muscle ...
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Why doesn't the rate of photosynthesis increase with increasing light energy (frequency)? [duplicate]
Why doesn't the rate of photosynthesis increase with increasing light energy (frequency)? I know that green light is not absorbed by chlorophyll, yet I am confused as to why this certain "...
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What are the physiological effects of retinal exposure to 380–400nm light?
There are two categories of sunglasses: UV380 sunglasses block all light with wavelength 380nm or lower, while UV400 sunglasses block all light with wavelength 400nm or lower.
This made me wonder, ...
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Do SILK fibres let light pass through it?
The reason given by Wikipedia for silk fibres being lustrous is that:
Silk fibres have triangular prism-like structure, which allows them to refract the incoming light at different angles.
By my ...
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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 ...
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Why is 450 nm monochromatic light perceived as blue or violet depending on its intensity?
Trying to do some color matching I purchased a 450 nm laser. I expected monochromatic light of this laser to have similar properties to those of all others I've already played with — 808, 640, 520, ...
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Can human perception differentiate between monochromatic and polychromatic light?
Maybe monochromatic is not the right word, what I mean is light consisting of a single wavelength (i.e. a spectral color) versus light composed of photons of multiple wavelengths (intermediate color).
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Is evolution the reason why water is colourless for our eyes?
Liquid water is transparent to most of the visible spectra, whereas it absorbs infrared.
Similarly, the air is almost transparent to the visible spectra too.
Could these be the reasons why our eyes ...
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Are mosquitoes attracted to blue lights in particular?
I've been confronting the fact since childhood that mosquitoes are attracted to lights, especially blue lights. Now I know that all insects including mosquitoes are attracted to bright light but I ...
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Are there any studies on the solar latitude limits of different plant species, beyond which they wouldn't thrive even with suitable weather?
Not sure whether this belongs here or in the Gardening & Landscaping StackExchange, but here goes...
According to maps provided in the paper Present and future Köppen-Geiger climate ...
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A poor man's COVID-19 vaccine? [closed]
If person A is infected (COVID-19) and person B is not, could the following work as a vaccination? Person A exhales (coughs?) into a a transparent bag. The bag is radiated for a long time with a ...
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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?
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What is the simplest way to demonstrate the germicidal property of UV light?
This is intended for a high school project. I am familiar with the one that studies growth of e coli over time in a petri dish but I a bit concerned about as to how safe a demonstration of this nature ...
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Blue light in a fridge. Is it really beneficial or just marketing?
Recently while visiting a shop with electronics I saw a fridge with a huge advertisment sticker going more or less like this:
There's blue light source in this fridge so there will be less bacteria ...
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Effect of light intensity on the frequency of stomata
According to this article, the frequency of stomata increases with an increase in the intensity of light. What I inferred from this is, since the rate of photosynthesis increases at higher light ...
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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,...
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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 ...
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Why does vision gradually becomes dimmer in bright setting?
I don't know if this is only happens to me, but if I am in a well lit room and I stare at one point or just look at one area without moving my eyes around my vision in that specific light setting ...
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Killing microorganisms on agar plates?
If I grow microorganisms on agar plates and I expose them to UV light. How exactly will I know that the microorganisms have been killed? I was watching a video that showed spots in the petri dish ...
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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.
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Why do ...
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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 ...
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Do flies avoid infrared light?
If flies avoid IR light, many places can be kept free from flies using IR light. We see insect repellers in many restaurants, but they don't seem to work well. Can IR be a safe & effective ...
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