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Hot answers tagged

23

You're talking about long-wave UV, or UV-A radiation. In the 80s, experts claimed that this was a safe wavelength. Protection against UV-A was not part of sunscreen in the early days. Consequently, UV-A was (and still is) used in tanning beds due to its perceived safety over UV-B. However, a lot of research has been done since. UV-A is well understood now ...


20

Short answer The visible spectrum has the highest energy in sunlight at the earth's surface, explaining the gross location of the visible spectrum in life on earth. The specific frequency range varies across species and can be explained by species-specific survival strategies. Background When you look at the solar light spectrum at the earth's surface the ...


17

Short answer In humans it is basically the red choroid plexus in the back of the eye you are seeing on a flashed photo, while it is the green-reflecting tapetum lucidum in dogs. Background The red-eye effect in humans was explained nicely by Yale Scientific Magazine, and I adapted the following text from that source: The human eye can effectively adjust to ...


14

Your retina contains both rods and cones. Cones are color sensitive, slow, and concentrated near the center of your field of vision. Rods are "light" sensitive, fast, and concentrated near the periphery. You want to be able to respond quickly to a threat "in the corner of your eye" without needing to see the color of the threat. This is nicely explained by ...


13

You will be interested in Aphakia, which is the lack of an eye lens usually through surgery but sometimes from birth. These individuals supposedly see UV as a whitish-blue or whitish-violet: This appears to be because the three types of colour receptor (red, green and blue) have similar sensitivity to ultraviolet, so it comes out as a mixture of all ...


12

Infrared wavelengths are EM waves of longer wavelengths than visible light. Also, visible waves are more energetic than IR waves. Because of this, Visible light has the ability to excite organic receptor molecules in our eyes called Rods and Cones. These molecules stimulate cell responses and in turn excite cell responses in our nerves called an Action ...


12

Short answer The effect you describe is called a negative after image. It can be explained by adaptation effects of the photoreceptors in the eye. Background source: Dresden University Steadily fixate on the black lightbulb for thirty seconds or more and then immediately turn your gaze to the white region on the right. The illusionary glowing white bulb ...


12

tl;dr: Sort of? Logically, either red or blue light should be sufficient. Chlorophyll a and chlorophyll b preferentially activate different photosystems, and both photosystems are required in green plants. Practically, we're in luck and someone has actually done the experiment. As the original study reports, plants need a little blue light to grow into ...


10

Dogs, cats, and many other mammals have a Tapetum lucidum which reflects light back through the retina to help with night vision. Humans don't have this layer. The tapetum is probably reflecting green light that would have normally been absorbed.


10

Firstly, note that "eye color" is actually iris color. The person with a lighter iris will have more straylight compared to person with brown iris: The graph represents Intraocular straylight of the age-matched groups. Participants with light-blue-colored iris showed significantly higher values for intraocular straylight than those of the other groups. ...


10

Most of the light from the sun doesn't actually reach the earth's surface due to the atmosphere. [source] So the light reaching earth includes near-UV, visible, near-IR and a band of radio waves. Seeing any other part of the spectrum would be impossible since it doesn't reach earth. You asked why we only see in the visible light range; this is due to ...


10

Short answer The increased fear responses during the night are believed to be mediated by elevated corticotropin-releasing hormone (CRH) levels in the brain that drive the fear responses in the amygdala. Background Fear responses can be experimentally assessed by recording the startle reflex. For example, loud noises can evoke gross startle responses in ...


8

You seem to have many misconceptions about how we see and how that relates to light. I'll address them one sentence at a time: Why are we able to differentiate between colored objects without the presence of light? Answer: the premise of the question is wrong: we aren't able to differentiate between colors without the presence of light, because we aren't ...


7

Please allow me to start by saying I know nothing about LEDs, so my answer isn't going to address your analogy. I'm also going to keep it more simple. Can the retina emit light? Yes. The retina is able to give off light in the form of fluorescence. Since fluorescence is the emission of light by a substance (granted that substance must first absorbed ...


7

This is a good question. The first thing to note is that human colour vision is very complex and still poorly understood. If you visit the wikipedia page on RGB, you will find that this correctly mentions that the S, M and L cones are most responsive to violet, green and yellow wavelengths respectively (which answers your first question - calling the cones ...


7

Vision is based on a protein interaction with a molecule called retinal from vitamin A. Wavelengths of light in the visual range cause a photoisomerization of retinal (a cis- to trans- change), which is sensed by the protein that is "holding on" to the retinal. Wavelengths that do not cause this photoisomerization cannot be sensed by the photoreceptors of ...


5

There are some limits on what light can be detected biologically based on physics and chemistry. Although there are animals that can sense more UV or more infrared than humans, they are still subject to these limitations. How Vision Works The way most types of vision operate is by using photons to cause a conformational change in an opsin protein by ...


5

[D]o we fail to see non visible light because our eyes lack the receptors for other frequencies, or does our brain receive signals that it just dumps because it has not developed to process the information? It is because our eyes lack the receptors for other frequencies. Humans have 3 'color receptor' called cone cells. We have three types of cone cells, ...


5

There are (at least) two sides to this story. One is direct DNA damage being caused by UV-B light which happens to have photons with just the right amount of energy to interact with thymine. This has been known, and assumed not just during the 80s, but until the late 2000s to be The One major thing that causes cancer, or trouble in general (there's papers ...


4

Some functions of non-green flower colors: #1: plant-animal interaction. Flower colors act as signals received by animals with eyes (e.g., pollinators, which many plants need to attract in order to reproduce). However, it sounds from your question as if you're looking for other physiological effects. Two that come to mind are: #2: heat. Flower color and ...


4

As far as I know there are 5 receptors for far-red and red light which are the phytochroms(phyA-phyE) Its all about the ratio between red and far-red light. Each phytochrom has an inactive(PR) and an active(PFr) conformation. phyA is the only phytochrom which is activated by far-red light, so its active state is PR. (Only if the ratio between red and far-...


4

First thing to note is that the absorption spectrum of chlorophyll A and chlorophyll B is similar but not the same. The reason for the appearance of absorption spectra is because the light is composed of photons of light. Different photon has different oscillation frequency and energy. The essence of Chlorophyll absorption is absorbing photons. After ...


4

Multiple studies have found moths along with most other insects to be significantly more attracted to lamps that emit smaller wavelengths such as ultraviolet (UV). Some species of moth appear to be more attracted to shorter wavelengths than others. The visibility of the light to the moth, the distance between the moth and light, and the brightness of the ...


4

Blue light means wavelengths that appear to the human eye as blue when they are presented alone. This light is important for sleep/wake cycle regulation because this is the wavelength that cells that participate in this regulation respond to. "White light" is light that covers the full visible spectrum; sunlight, for example, is fairly white. However, that ...


3

Behar-Cohen et al. notes the periphery of the cornea has a focusing effect: UVR incident from the periphery is refracted into the eye, and due to the focusing effect of the cornea, UV radiation is on average 22-fold stronger at the nasal limbus, which is the typical site for pterygium and pinguecula. Moreover, UV radiation is on average eight times ...


3

This is UV-C radiation and light of this wavelength (which is emitted by low pressure mecury lamps) can indeed be used for disinfection purposes. The nucleic acids (DNA and RNA) has an absorption maximum for UVC radiation at 265nm, causing DNA/RNA damage. The radiation of the mercury lamps is only a little below, making them still quite effective (see the ...


3

Lets start with the absorption spectrum first (image from the Wikipedia page in chlorophyll): What you see in the figure is the absorption of light thoughout the visible spectrum by chlorophyll a (blue) and b (red). The higher the peaks get, the higher the absorption is. What we can see, is that chlorophyll absorbs light roughly until 500 nanometers (nm) ...


3

It seems like they are not affected by fluorescent light frequency. I did not find anything about their visual sampling rate. Their hearing is between 0-200Hz with an average of 86Hz so I guess the visual sampling rate is under this, but that's just a guess. We conclude that at the illumination levels used in this experiment, the hens did not perceive ...


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