# How is light able to form images? [duplicate]

This question already has an answer here:

Everyday we see ourselves in mirror and this is due to light which forms our image after reflection ( may be refraction sometimes) . But I wonder how can light carry the image. How is it possible that massless particles (or waves maybe, which is not an issue now ) can carry the image of the source from which they come or object by which they got reflected bat a tremendous speed ?

I know that things we perceive as they are because of our eyes but the point of that our eye must also perceive things which really occur. Like if the light rays are coming from an object at infinity and incident on a concave mirror, then they get converged to points in the focal plane and we say that a real image has been formed there. Then the question is how light made that image (which may be perceived by our eyes) ?

## marked as duplicate by Yashas, ZeroTheHero, Jon Custer, John Rennie, sammy gerbilMar 28 '17 at 1:14

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

• Each particle of light (or a ray of light) carries information about one point of an image. The wavelength of light carries information about the colour. A collection of these particles of lights (or rays of light) together form an image. The previous question's answer explains it for a specific case of a lens but that answer still holds for any general case. – Yashas Mar 27 '17 at 10:49
• Note that just because light of red wavelength is entering your eye, it does not mean that the source is colored red. If your eye receives both red light as well as green light, you see yellow. – Yashas Mar 27 '17 at 10:56
• How do each particle carry information about the object ? Is it their fundamental property and cannot be explained? That's what I exactly wanted to ask. I am aware that how images are formed which is answered in the question ( @yahas samaya) and just wanted to be explained of this property of light. Thanks for your help but you understood my ques wrong or may be I am unable to present it . – Abhinav Dhawan Mar 27 '17 at 10:57
• The light is a particle (or a wave). Its characteristic properties are wavelength, frequency, speed, energy and momentum. The five properties are related by the following equations: $$E = pc$$ $$E = hf$$ $$c = f\lambda$$ The wavelength of light carries information about the color. Light with wavelengths of around $700nm$ appear red and light whose wavelength is around $450nm$ appear blue. You should google "electromagnetic spectrum visible light" to see how wavelength relates to color. – Yashas Mar 27 '17 at 11:01

## 2 Answers

Just think about how you "see" an object.

Either by reflect or by self generation an object emits light from every point on its surface.

These rays of light emanate from a point and so are diverging.

Some of these rays of light pass through the cornea and lens system and hit the retina.

For a "perfect" image to be formed all the rays of light from one point on the object which enter the eye must hit one point on the retina and they all must have taken the same time to travel from the object to the retina (or arrive in phase).
Also the light from the points on the object which are nearest neighbours to the point under consideration on the object must arrive at the retina at points which are in the same relative positions to the point under consideration as they were on the object.

In the case of the reflection in a mirror the eye can only process the reflected light which "appears" (back produce the rays entering the eye) to come from a region behind the mirror which we call a virtual image of the object in front of the mirror. The virtual image acts like a light emitting object as far as the eye is concerned. Thus, virtual images are essentially seen due to the action of the eye.

Again there is a one to one correspondence between points on the object in front of the mirror and points on the virtual object behind the mirror.

The light which leaves the object can be catagorised in terms of the direction it is moving, its wavelength/frequency/colour and its intensity.
An optical system can be "designed" to bring that light together to reproduce an entity, the image, which is a point to point reproduction of the object.
So if the retina was not there the light rays which had formed the image on the retina would carry on moving in a divergent manner and those light rays would appear to come from where the image had been formed on the retina.

You are correct, light only carries information in the form of wavelengths. When light enters the eyes, specific wavelengths trigger specific cones. It's the location of the cone which provides the brain the information needed to create images by contrast. Because we have binocular vision, our brain combines the images from both eyes and builds a 3 dimensional visual representation of our surroundings.

When they say a real image is formed at the focal point you have to place a screen at that point to see the image or you have to position yourself at that point, at which time you will see an image in the mirror.

• Bifocal does not mean that you have two eyes; it means that a lens/mirror has two focal lengths. – Yashas Mar 27 '17 at 10:54
• Thanks a lot. You're saying that a specific wavelength will make us perceive a colour and that is how an image is made. Yet I have another question which may be posted separately but as it is related I am posing it now. – Abhinav Dhawan Mar 27 '17 at 11:30
• You said that light has a color associated with it by the virtue of its wavelength. But I have read that color is associated with frequency and it justified this by saying that after refraction the frequency does not changes and so do the color, but wavelength changes . It explained it using wave fronts which I couldn't understand. I would be obliged by your help in this matter. – Abhinav Dhawan Mar 27 '17 at 11:37
• Then why doesn't the color changes if wavelength changes after refraction. Like we are seeing something inside water, its color does not changes but wavelength does... – Abhinav Dhawan Mar 27 '17 at 11:44
• This may help. tedmontgomery.com/bblovrvw/emails/lightfrequency.htmlp – zane scheepers Mar 27 '17 at 11:49