Does focusing light with a lens create a light gradient?

In summary, the conversation discusses the concept of focusing light with a lens and its potential to create an intensity gradient which could be mined for energy. The idea is compared to concentrated solar power and the properties of the eye are mentioned as an example. Ultimately, it is determined that the fovea, the area of the retina with the highest visual acuity, is not necessarily the area with the highest concentration of photons due to the complex nature of light entering the eye.
  • #1
query_ious
23
0
*disclaimer I am not a physicist

Had a weird thought the other day - when you focus light with a lens, for example a magnifying glass, you basically increase the 'concentration of photons' at a certain point, right? But then energy is conserved... so wouldn't focusing some of the light on one spot then create a 'lack of light' or shade on another, adjacent spot? And might this not create an intensity gradient = a heat gradient = something which could be mined for energy? I mean I asked a physicist friend who said that because of diffraction focusing light doesn't create an 'energy peak' at the focal point but rather a series of rings each of weaker intensity but this still sounds like a type of gradient to my untrained ears...

What say you oh great hivemind?

Thanks :)
 
Science news on Phys.org
  • #2
Yes, focusing the light will increase the light falling on a small area at the expense of reducing the light falling on a larger area. The total light still remains the same, you are just moving some of it around. This is hard to see outside with a magnifying glass, but it may be easier it you shine a small flashlight into the magnifying glass inside in the dark.

This effect is already used to generate power in solar power stations and is known as concentrated solar power: http://en.wikipedia.org/wiki/Concentrated_solar_power
 
  • #3
cool, thanks :)
 
  • #4
Also, it's fun to think of the eye as an example of light focusing.
Found quite a bit of info online on the general properties of the eye and a smaller amount on the total numbers of photons hitting the retina but none that explicitly described the spatial distribution of impacting photons.

So a rather silly back of the envelope calculation -
Retinal area is about 1000mm^2
Fovea centralis area is about 2.5mm^2
so fovea area is ~500-fold smaller than total retina
+ let's assume 90% of incident light is redirected to the fovea (my wild guess)
then remaining 10% of light redistributed over 500-fold larger area gives 4 orders of magnitude difference in number of incident photons per foveal area.
Which, at 4e-19 J per photon at 500nm or 2e-22 degrees C per photon is not much of a heat difference... ah well
 
  • #5
query_ious said:
+ let's assume 90% of incident light is redirected to the fovea (my wild guess)

Not true. Just look off to the side of a bright light. The light from the lightbulb will be focused off of the fovea.

Your original example just dealt with a single source of light. In real life light is entering the eye from every angle and a real image is formed on the retina that is a mirror image of the scene in front of the eye. The fovea is simply the area of the retina that is at the center of the eye's optical axis. It is on the optical axis that most aberrations inherent to any optical system are minimized and visual acuity is maximized.
 

Related to Does focusing light with a lens create a light gradient?

1. Does the shape of the lens affect the light gradient?

Yes, the shape of the lens can affect the light gradient created. For example, a convex lens will create a different light gradient than a concave lens.

2. Can the material of the lens affect the light gradient?

Yes, the material of the lens can also affect the light gradient. Different materials have different refractive indexes, which can impact the way light is focused and create different gradients.

3. Does the distance between the lens and the light source affect the light gradient?

Yes, the distance between the lens and the light source can impact the light gradient created. The closer the lens is to the light source, the more focused the light will be and the sharper the light gradient will be.

4. Is the light gradient created by a lens always linear?

No, the light gradient created by a lens is not always linear. It can also be curved or even non-uniform, depending on the shape and properties of the lens and the distance between the lens and the light source.

5. Can a lens create a light gradient in all directions?

No, a lens can only create a light gradient in the direction of its axis. The light gradient will be most prominent in this direction, while the light will be less focused and less gradient-like in other directions.

Similar threads

  • Optics
Replies
10
Views
1K
Replies
9
Views
513
Replies
10
Views
3K
Replies
5
Views
1K
Replies
32
Views
7K
Replies
4
Views
1K
Replies
7
Views
3K
Replies
2
Views
2K
Replies
2
Views
1K
Back
Top