What is Sunlight: Definition and 106 Discussions

Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when the Sun is above the horizon. When direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When blocked by clouds or reflected off other objects, sunlight is diffused. Sources indicate an "Average over the entire earth" of "164 watts per square meter over a 24-hour day".The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a requisite for vitamin D3 synthesis and a mutagen.
Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun. A photon starting at the center of the Sun and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface.Sunlight is a key factor in photosynthesis, the process used by plants and other autotrophic organisms to convert light energy, normally from the Sun, into chemical energy that can be used to synthesize carbohydrates and to fuel the organisms' activities.

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  1. S

    Can a rise in sunlight exposure cause magnesium depletion?

    I have recently learned that taking vitamin D supplements can cause a dip in magnesium, because Mg is used as a cofactor to process the vitamin. Does this apply to a sudden lifestyle change from very little exposure to lots of exposure to sunlight? (I am asking this as a purely theoretical...
  2. T

    Globe Earth question: Percent of the Earth receiving sunlight at a given time

    I recently stumbled on a problem I can't solve. For background, there is a recent story from July 8 about 99% of people receiving sunlight at 11:15 am. Anyone can google it and it's explained fairly well at time and date. There is an illustration. Here...
  3. M

    B Sunlight reflection on planets

    If the Sunlight lets say would go off, exactly how long would astronomers on Earth still see sunlight reflected on the surface of Mercury, Venus, Mars, the asteroids, Jupiter Saturn, etc.? I mean Sun goes dark at 0:00 from the point of view of Earth-based observers. At that exact moment, if...
  4. yohananregal

    How's it possible that 70% of Earth receives sunlight simultaneously

    How did you find PF?: Google Hello, I am new here. I am wondering, how is it possible for nearly 70% of the spherical Earth to be illuminated by the sun every July 8th? How can a sphere be illuminated beyond 50% with a single light source. How do we explain this?
  5. H

    I Double slit fringe visibility with sunlight

    Hi Pfs, I know that Young made his double slits experiment with sunlight and i would like to know the best value of the fringe visibility on the screen. The visibility is equal to (Imax - Imin)/(Imax + Imin) thanks
  6. H

    Lawn/Garden Convex Mirror in Backyard to reflect sunlight onto the house

    Hello- I am starting a project to get direct sunlight onto the house by placing convex mirrors on the outside stone fence of the backyard since it is the only place of my property that is not shaded by other houses in the neighborhood. For that, I need to calculate the size of the mirrors...
  7. K

    Common chemicals released under sunlight exposure?

    What are the common and/or possible chemicals that could release from clothes or bedclothes when it is exposed to sunlight? Since there are many different textures and additives so I am concerned about the common chemicals that could release I roughly know that sunlight will break a lot of...
  8. N

    I Does luminous efficacy differ between direct and reflected sunlight?

    With the total visible light flux being equal does reflected sunlight (by the sky, environment or shading/light redirecting surfaces) have a smaller total energy per luminous flux and therefore resulting heat gain than direct sunlight? Possibly caused by a larger luminous efficacy, i.e. more...
  9. E

    B Why does the Sun need sunlight?

    A photon is different from an electron. At least by the fact that it is neutral. But, flying into the silicon lattice, it knocks out an electron and takes its place. That is, it becomes an electron. How does such a magical transformation happen? I may be wrong, but I think that a photon becomes...
  10. K

    Is reflected sunlight damaging to the eyes?

    Is reflected sunlight on any surface otherwise than mirror or mirror-like surface safe for human eye? I can imagine mirror surface could reflect a lot of sunlight directly, making little difference from staring at the sun directly How about reflected sunlight on white but obaque surface? Could...
  11. S

    Is it possible to make a "laser" etcher using "piped" sunlight?

    This is an older idea of mine which I just remembered when reading the thread about using a light-bulb to make a laser. The concept is this: 1: Focus light from the sun into a point using a magnifying glass, which we know can burn things. 2: at the point of focus, place another lens which will...
  12. E

    Question about variations of the Sun's path over long periods of time

    Hello. I am a filmmaker writing a screenplay and I am in need of technical support to validate a method being used in the film. I am going to post this in the Earth Science forum but I'll copy it here, in case anyone reading this might know. Thank you all! "I am wondering if shadows cast...
  13. Q

    B Is sunlight through gaps in leaves during an eclipse decohered?

    Is the reason you can make out the shape of the sun and the moon is because the gaps between the leaves cause the light to be photons instead of waves?
  14. V

    B Seeing Merging Shadows in the Sunlight

    Today when I was standing beside a container in sunlight I observed that the shadow of my hand merged at a certain distance with of the container even though their was enough distance between my hand and container for light to pass is there a reason?
  15. L

    Does the angle of the magnetic field affect sunlight?

    With talk of the Earth's magnetic field slowly moving, (enough to cause navigational issues I've heard) does it effect how the sun's ray hit us? For example, the Northern Lights are solar partials interacts with the magnetic field (I think). If the poles moves, would it affect the effectiveness...
  16. M

    I Sunlight refraction at sunset at different latitudes?

    “Sunlight due to refraction is greater in higher latitudes than at the equator because of shallower angles of incidence to horizon. It takes longer for Sun to go down half a degree at sunset at shallower angles.” When I draw a diagram of sun rays incident towards the earth, the angle appears to...
  17. another_dude

    Why doesn't sunlight have infinite energy?

    In school we are taught that sunlight contains all different frequencies of light. Also that each frequency has it's own unique wavelength and energy (per photon). So my question is that if there are infinitely many different wavelengths of light (much like infinitely many numbers in an...
  18. physea

    How Much Heat Energy Can Be Harvested from Sunlight Per Square Meter in the UK?

    hello! I find a lot of information about the energy of sunlight per square meter in the UK region. (https://photonenergy.co.uk/new-build-solar-pv/solar-map-of-the-uk) However, these kWh/m2 must be in the form of light energy or perhaps electricity (after adjusting with an efficiency...
  19. HastiM

    Change of radiation pressure of sunlight w.r.t. distance

    Hello, Let me first describe the situation I am thinking of: suppose we consider an object in the form of a square with some thickness (e.g. a mirror). Suppose further, that the gravitational force pulling the object towards the sun and the radiation pressure due to the sunlight are in balance...
  20. 1977ub

    Peripheral Vision / Sunlight Damage

    If I am walking on a sunny day, looking mostly straight ahead, and the Sun is close to straight ahead but elevated 30 to 45 degrees so I'm not looking directly at it, is there a risk of vision damage?
  21. S

    B How long is a beam of sunlight?

    How long is a beam of light or sunlight?
  22. K

    Sunlight absorption spectrum and colors in sunlight

    Hi. In physics articles, they say that sun light is white, and contain all colors. But they show say that the Sun's atmosphere absorb light at certain wavelengths, causing the intensity of the light at this wavelength to drop and appear dark. And the absorption spectrum looks like this...
  23. A

    Directing sunlight into the optical fiber

    Hello Is it possible to direct sunlight into the optical fiber by magnifying glass and a prism like the image below? if yes , what shape of prism should i use to do this? Thank you
  24. A

    I On the Moon, could you melt dirt by focussing sunlight?

    On the Moon, could you melt dirt into bricks and paths by focussing sunlight? If you had a large metal parabolic reflector and just pointed it at the ground, would it melt the dirt? Could you make a path that way? In the vacuum there would be less escape of heat to cool it. If you piled dust...
  25. S

    Mystery of Reflected Sunlight 73 Miles Away - A Man's Quest

    I read in a book about a man who saw the sun reflected off a distant object on a mountain some 73 miles away in clear visibility. He saw this on many occasions and always wondered what it could be. He states that he asked two of his friends who were going that way if they would check it out...
  26. F

    Xenon lamps and sunlight simulation

    Hello, Would a set of inexpensive xenon lamps purchased at the hardware store simulate sunlight pretty well in terms of spectrum (visible and IR) and intensity? Solar simulators are expensive devices but I wonder if I can get by with an array of less costly xenon lamps. thanks
  27. O

    Sunlight, Intensity, electric field RMS

    Homework Statement Estimate the rms electric field in the sunlight that hits Uranus, knowing that the Earth receives about 1350 W/m2 and that Uranus is 19.2 times farther away from the Sun (on average) than is the Earth. Homework Equations I=cεoErms2 E=V/d The Attempt at a Solution Eearth=V/d...
  28. ReneVeerman

    Freshwater (industrial scale) from seawater, on sunlight

    i have this idea to produce fresh water for farming and all the other uses of fresh water, from seawater, on sunlight, using mostly/only off-the-shelf parts.. i am currently not able to pursue this idea myself due to financial constraints, so i thought i'd float the idea here looking for some...
  29. Alan Arqueza

    Why Was Yesterday's Sunlight Brighter Than This Morning?

    Yesterday morning the lighting from the sunlight made everything brighter until 11:50am Pacific Daylight time. I am in the San Francisco Bay Area in Northern California. Can you explain why sunlight on 13 July 2016 appears to be 'brighter' than this morning?
  30. S

    Any sunlight band pass filter for 400-700nm of EM Spectrum?

    This 400-700nm slice is the Photosynthetically Active Radiation (PAR) required of plants and, for many applications, there is much unwanted UV and IR heat outside of it. Is there any known translucent material or film that will pass a high % of that 400-700nm wavelength from sunlight while also...
  31. D

    Space Cloud to Reflect Sunlight?

    With the growing threat of global warming, couldn't we launch a series of rockets into space filled with water and have them discharge the water to create clouds in space between the sun and earth? The water vapor cloud would absorb and deflect some of the heat. It wouldn't have to be very...
  32. skepticwulf

    Do plants need direct sunlight?

    We all know the famous theory that an asteroid hits the Earth and kill the dinosaurs by starting a chain reaction where the dust is all over the atmosphere preventing sunlight to reach plants causing them eventually to die thus causing herbivorous to die thus causing carnivorous to die. But when...
  33. Y

    Can We Create a Sun-Shaded Assembly Area for Our School?

    This is my school's assembly area : The place is generally used for the assembly and various other things. But the problem is that it receives a lot of sunlight and it is difficult to use it during the later part of the day. So, I would like something like a roof, which doesn't entirely...
  34. mnmman

    Sunlight Intensity Concentrator - Idea to boost solar energy

    So I had this idea and I want to run it by some people and see if it's 1) possible 2) worthy of pursuing further 3) a good idea. I don't have a degree in engineering or physics, I'm currently studying chemistry and am taking physics 2 (E&M) right now, so excuse me if I don't use the correct...
  35. G

    Concentrating sunlight to accomplish projection (Art project)

    Hello! First of all I want to say that I am not a physicist, but an artist currently doing my master thesis. I have been trying to build a solar powered slide projector. It works very simple – I reflect sunlight through a slide and enlarge it with a lens. My problem was that I wanted more...
  36. P

    Are there gaps between the rays coming from the sun?

    Hi! I have a question regarding the radiation coming from the sun. It might seem stupid to some people but I would really like to know how this works. When you see images of the sun's rays reaching the Earth for example on this image from wikipedia (see attached image). The rays are almost...
  37. shmijda

    Which has the most intense sunlight hitting it?

    Homework Statement Which has the most intense sunlight hitting it?Question 2 options: A point on the Equator at sunset The North Pole at Noon on the Summer Solstace Montreal at Noon on the Spring Equinox The South Pole on the (Northern hemisphere) Summer SolstaceHomework Equations none The...
  38. R

    Convert sunlight to electricity in a given area

    Homework Statement Question: Lake Mead is formed by the Hoover Dam, and while it actually changes in area and volume, consider it has an average area of 100,000 acres. Assume that 250 W/m^2 of sunlight falls on Lake Mead, how much electricity could be produced if this lake area was covered by...
  39. M

    How does our body acquire vitamin D from sunlight?

    Can anyone explain how we acquire vitamin D or which chemical reaction takes place ?
  40. A

    Exploring Sunlight in the Atmosphere: IR Wavelengths

    Can anyone speak on the spectrum of sunlight reaching the upper atmosphere and the surface ? Specifically I interested in finding out if there are any IR wavelengths disproportionally represented when compared to the original source. Please limit responses to constructive ones.
  41. N

    Polarization of Laser vs Sunlight

    Hi all, I'm implementing a computer vision system with a near-infrared laser and a NIR bandpass filter. It shines a laser on things and looks for a reflection. I'm getting a bunch of interference from sunlight and was thinking of using a polarizing filter to cut some of the sunlight out...
  42. B

    Collimating Sunlight: Can It Be Done?

    It seems like it should be easy to use two lenses to 1: focus light into a small point then 2: use a stronger lens past the focal point to keep the beams fairly parallel. Experimentally, I have not been able to achieve these results. I have an LED flashlight which can project a fairly tight...
  43. B

    Power from LED bulb in sunlight

    My son is working on his science fair project. I had told him that LED bulbs produce voltage in sunlight and he's been exploring that and is trying to see if he can charge a cell phone using LED bulbs under a light source. Using dozens of small LEDs, he is producing about 5v under a light...
  44. J

    Intense sunlight and its effects on contrast in shadows.

    First, let me just say that, while I tend to be knowledgeable on a wide variety of topics, I am absolutely atrocious with details such as names, times, and specific values. A friend of mine has decided that I'm imagining an effect that I have experienced on countless occasions and which I...
  45. A

    Can sunlight be used as an antiseptic?

    Sunlight contains UV radiation. UV lamps are used to destroy the reproductive organs in pathogens. Therefore, in desperate times could one remain in the sun to keep a wound clean?
  46. B

    Diffraction Patterns: Sunlight vs. Laser Beam

    Hi, I was wondering what the diffraction pattern would be like if the suns light is diffracted through a pin hole or double slit diffraction grating compared to that of a laser beam? thanks.
  47. S

    MHB A Prayer for Sunlight: A Blessing

    Prayer Sun that gives all things birth, shine on everything on earth. If that's too much to demand, shine at least on this our land If even that's too much for thee, shine at any rate on me.
  48. J

    UV Light and UV glue And Sunlight

    Simple question will UV glue that is supposed to be dried under a UV light dry or harden if taken and placed in direct sunlight? John
  49. C

    Pen ink faded off upon heat(or maybe sunlight)

    Last month I bought one of those pens which you can rub off your writings with a kind of rubber at the end of the pen. I was so happy because I don't need to use correction pens anymore, so I did all of my maths exercises with that pen. One Friday, my books was very heavy so i left some inside...
  50. T

    Wavelengths of sunlight, blackbody radiators, Planck's law, CCT

    A blackbody radiator emits radiation across the entire radiation spectrum. The "temperature" of the blackbody radiator (measured in kelvin) can be directly calculated from the peak wavelength of its radiation using http://en.wikipedia.org/wiki/Wien's_displacement_law"]Wien's[/PLAIN]...