Questions tagged [light]
Electromagnetic radiation, specifically the range of wavelengths visible to humans ("visible light").
113
questions
2
votes
0
answers
20
views
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, ...
0
votes
0
answers
24
views
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) ...
0
votes
1
answer
44
views
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 ...
- 103
0
votes
0
answers
19
views
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 ...
- 140
3
votes
0
answers
73
views
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 ...
- 39
0
votes
0
answers
29
views
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 ...
- 161
0
votes
0
answers
21
views
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, ...
- 161
10
votes
2
answers
3k
views
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 ...
- 259
2
votes
1
answer
103
views
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 ...
- 23
0
votes
0
answers
47
views
Photosynthesis at the atomic level
This seems like it should be a simple question to answer, but I haven't been able to find a response anywhere on the Internet: when photosynthesis is initiated by a photon hitting the chlorophyll in ...
- 161
0
votes
0
answers
29
views
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 ...
- 1
0
votes
1
answer
80
views
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 ...
- 101
5
votes
1
answer
179
views
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 ...
- 478
7
votes
1
answer
796
views
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 ...
- 581
6
votes
1
answer
140
views
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 ...
- 161
1
vote
0
answers
46
views
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 ...
- 111
0
votes
2
answers
120
views
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 ...
- 11
-1
votes
3
answers
938
views
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 ...
- 131
0
votes
1
answer
113
views
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 ...
2
votes
1
answer
139
views
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 ...
- 191
2
votes
0
answers
15
views
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 ...
- 133
-3
votes
2
answers
118
views
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 "...
- 3
-2
votes
1
answer
93
views
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 ...
- 107
1
vote
2
answers
691
views
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, ...
- 975
1
vote
0
answers
53
views
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 ...
2
votes
0
answers
22
views
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 ...
- 131
1
vote
1
answer
153
views
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 ...
- 135
1
vote
1
answer
906
views
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 ...
- 11
1
vote
1
answer
49
views
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 ...
- 13
6
votes
1
answer
665
views
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 ...
- 1,625
0
votes
1
answer
128
views
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 ...
- 392
14
votes
2
answers
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 ...
- 325
0
votes
0
answers
325
views
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 ...
0
votes
0
answers
40
views
Does cataract condition cause red film when sun is shining?
Since two years ago I have a red film in my field of vision when the sunlight (or a white spot) is at the border (or even lightly behind) of the vision field, the red color is especially obvious at ...
1
vote
1
answer
192
views
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 ...
- 11
2
votes
1
answer
64
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 ...
- 23
2
votes
2
answers
752
views
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, ...
- 395
3
votes
0
answers
109
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 ...
- 59
2
votes
0
answers
71
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 ...
0
votes
1
answer
49
views
Why did we evolve to be able to see this specific set of wavelengths only? [duplicate]
It is understandable that life didn't evolve the capability to sense all wavelengths of light, it simply didn't need it. My question is, why did it evolve the set of wavelengths it has, for example, ...
- 223
1
vote
1
answer
121
views
Does night mode on iPhone really help?
Okay so I know that night mode is supposed to filter out blue light that is bad for the eyes, but is it really more helpful than annoying? At night I do use it when I’m on the phone but it doesn’t ...
- 17
0
votes
0
answers
38
views
What is the difference between GFP and rhodopsin?
GFP and Rhodopsin are both fluorescent proteins. What is the main difference between GFP and Rhodopsin in terms of how they work? I know that their excitation and emission wavelengths are different, ...
- 927
2
votes
1
answer
466
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 ...
- 171
1
vote
0
answers
620
views
Can light destroy auxin?
In my biology textbook, it says that plants grow towards light because auxin is laterally transferred from the light side to the shaded side, so more auxin stimulates growth and hence the plant bends ...
- 105
3
votes
0
answers
97
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 ...
- 125
2
votes
0
answers
33
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 ...
- 289
0
votes
2
answers
130
views
Do Vaccinium membranaceum plants need a minimum amount of darkness per 24 hours?
I have Vaccinium membranaceum (black huckleberry) seedlings growing in a greenhouse. I have the option of providing fluorescent light to the plants 24 hours a day.
However, it has occurred to me that ...
- 862
5
votes
2
answers
2k
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 ...
2
votes
0
answers
77
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 ...
- 382
1
vote
2
answers
134
views
Reaction centre in Photosystems of higher plants
In photosystems of higher plants, there are about 250-400 pigments (number wise) in a particular photosystem. Out of which,approx 170-180 pigments are of chlorophyll a molecules. And any one of them ...
- 382