Light, Shadows and Reflections — Complete Guide for Class 6

Switch on a torch in a dark room and point it at the wall. You see a bright circle of light. Now put your hand in front of the torch — and your hand’s dark outline appears on the wall. That dark shape is a shadow.

This simple experiment tells us three important things: light travels from a source, it moves in straight lines, and when something blocks it, a shadow forms. Everything in this chapter grows from those three ideas.

CBSE Class 6 Chapter 11 covers luminous and non-luminous objects, transparent/translucent/opaque, shadow formation, and reflection. These topics appear regularly in school tests and Olympiad papers.

Sources of Light — Luminous vs Non-Luminous Objects

Luminous Objects

Objects that produce their own light are called luminous objects.

Examples:

The Sun (our biggest source of light)
A burning candle
A lit electric bulb
A firefly
Stars (the Sun is a star!)
A burning matchstick

All of these produce light by themselves — they don’t need another light source.

Non-Luminous Objects

Objects that do NOT produce their own light are called non-luminous objects. We can only see them when light from a luminous source falls on them and bounces off into our eyes.

Examples:

The Moon — it does not produce its own light. It reflects sunlight.
A book, table, chair, your friend’s face — we see all of these because light (from the sun or a bulb) bounces off them.
Planets — Mars, Jupiter, and all other planets in our solar system are non-luminous. They shine by reflected sunlight.

A very common exam trick: “Is the Moon a source of light?” The answer is NO. The Moon is a non-luminous object. It only reflects light from the Sun. Never say the Moon gives its own light!

Transparent, Translucent, and Opaque Objects

Different materials behave differently when light falls on them. We sort them into three groups:

Transparent Objects

Materials that allow all (or nearly all) light to pass through them are called transparent materials. You can see clearly through them.

Examples:

Clear window glass
Clean water in a glass
Air
Clear plastic wrap
A glass lens

When you look through a clean glass window, you can see everything on the other side clearly. That is transparency.

Translucent Objects

Materials that allow some light to pass through but scatter it — so you can see a blurry outline but not clearly — are called translucent materials.

Examples:

Frosted glass (bathroom window glass)
Butter paper (also called tracing paper or greaseproof paper)
Oily paper
Thin cloth
Thin plastic milk bags
A lampshade made of thin paper

Hold butter paper up to a bright light. You can see that light is getting through — the paper glows — but you can’t clearly make out what is behind it. That is translucency.

Opaque Objects

Materials that block all light from passing through them are called opaque materials. No light gets through at all.

Examples:

A wooden door
A brick wall
A metal spoon
A book
Your hand
Cardboard

The three terms in plain language: Transparent = see-through clearly. Translucent = see light but not clearly. Opaque = cannot see through at all.

A clear glass window is transparent. A foggy frosted glass is translucent. A wooden door is opaque.

How Do We See Objects?

We see objects because light enters our eyes.

For luminous objects (like a bulb or the sun): the object itself sends light directly into our eyes.

For non-luminous objects (like a table or a friend’s face): light from a luminous source falls on the object, and the object reflects (bounces back) some of that light into our eyes.

So we never really see the object itself — we see the light reflected from it. In a completely dark room with no light source, you cannot see anything at all, even though everything is still there.

Light Travels in Straight Lines

This is one of the most important ideas in this chapter.

Light always travels in straight lines. It does not curve around corners, bend around objects, or go zigzag. This property is called the rectilinear propagation of light.

How do we know light travels in straight lines?

Experiment 1: Take three cards. Make a small hole in the center of each. Line all three holes up in a straight line. Hold a torch at one end. If the holes are perfectly aligned, you can see the light through all three. Now move the middle card slightly to the side — the light is blocked. This shows light only travels in a straight line.

Experiment 2: Stand behind a tree on a sunny day. The tree’s shadow falls behind you. The shadow is always on the opposite side of the tree from the Sun — because light from the Sun travels in straight lines and cannot bend around the tree.

The statement “light travels in straight lines” explains shadow formation, pinhole camera images, and why we can’t see around corners. This is the most important concept in this chapter.

How Are Shadows Formed?

Three things are needed to form a shadow:

A source of light (like the Sun, a torch, or a bulb)
An opaque object that blocks light
A screen or surface where the shadow falls (like the ground, a wall, or paper)

When an opaque object is placed in the path of light, the light rays cannot pass through it. The area behind the object that receives no light appears as a dark patch — the shadow.

Light travels in straight lines, so the shadow appears on the opposite side of the object from the light source.

A translucent object makes a faint, blurry shadow because some light gets through. A transparent object makes almost no shadow at all because most light passes through it. An opaque object makes the darkest, sharpest shadow.

Shadow Puppets

You’ve probably made shadow puppets by holding your hands between a torch and a wall. By bending your fingers into different shapes, you create different shadows — a dog, a duck, a bunny. This works because your hands are opaque and block light in the shape of your fingers. Since light travels straight, the shadow on the wall matches the outline of your hand.

How Shadow Size Changes

The size of a shadow is not fixed — it changes depending on:

1. Distance Between the Object and the Light Source

Bring the torch closer to an object (like your hand) → the shadow gets bigger. Move the torch farther away → the shadow gets smaller.

Why? When the light source is close, the light rays spread out around the object at a wider angle, creating a larger shadow. When the light is far away, rays are nearly parallel and the shadow is closer to the actual size of the object.

2. Distance Between the Object and the Screen

Move the screen farther from the object → the shadow gets bigger and blurrier. Move the screen closer to the object → the shadow is smaller and sharper.

3. Angle of the Light Source

When the Sun is low on the horizon (morning and evening), your shadow is very long. When the Sun is directly overhead (noon), your shadow is very short. We’ll cover this in detail later.

The Pinhole Camera

A pinhole camera is one of the simplest and most brilliant inventions in optics. It needs no lens, no electronics — just a box with a tiny hole.

How to make one: Take a cardboard box. Make a tiny pinhole in one face. On the opposite face, stretch a piece of tracing paper (this is the “screen”). Go into a dark room and point the pinhole at a bright object (a candle or window).

What you’ll see: An image of the object appears on the tracing paper screen — but it’s upside down and inverted left-to-right (called a laterally inverted and vertically inverted image).

Why upside down? Light from the top of the object travels in a straight line through the pinhole and hits the bottom of the screen. Light from the bottom of the object hits the top of the screen. Since light travels in straight lines and they cross at the pinhole, the image flips.

The pinhole camera proves that light travels in straight lines. If light could bend, the image would not form correctly. NCERT Class 6 expects you to explain the pinhole camera and why the image is inverted.

Fun fact: The human eye works on the same principle as a pinhole camera. The image on your retina is actually upside down — your brain automatically flips it so you see everything the right way up!

Mirrors and Reflections

What is Reflection?

When light hits a smooth, shiny surface, it bounces back. This bouncing back of light is called reflection.

A mirror is the most common example of a reflective surface. The mirror does not produce any light of its own — it is non-luminous. It simply reflects light that falls on it.

Other reflecting surfaces: the back of a spoon, calm water on a lake, a polished metal surface, a shiny tile.

What Does a Mirror Do to an Image?

Stand in front of a mirror and raise your right hand. In the mirror, the image seems to raise its left hand. This effect is called lateral inversion — left and right are swapped.

This is why writing looks reversed in a mirror. An ambulance has the word “AMBULANCE” written in reverse on its hood — so when drivers see it in their rearview mirrors, they read it correctly.

Lateral inversion = left-right reversal in a mirror image. The image in a plane mirror is the same size, same distance behind the mirror as the object is in front, upright, and laterally inverted. This is commonly tested.

Rough Surfaces and Scattered Reflection

A mirror reflects light in one direction — this is called regular reflection (or specular reflection). But a rough surface (like a wall or a sheet of paper) reflects light in many different directions — this is called diffuse reflection (or irregular reflection).

This is actually very useful! If walls reflected light like mirrors, you would be blinded every time you looked at a wall. Diffuse reflection from walls spreads light gently around the room, which is why you can read comfortably in a well-lit room.

Real Life Examples — Putting It All Together

Why can’t you see through a wall? A wall is opaque. All light is blocked. No light passes through to your eyes from the other side.

Why can you see through a window but not through a frosted bathroom window? A clear window is transparent — light passes through cleanly. A frosted window is translucent — light passes through but is scattered, making it blurry. This gives privacy while still letting in light.

Why does your shadow disappear on a cloudy day (or become faint)? On a cloudy day, sunlight is scattered in many directions by the clouds. Instead of parallel rays hitting you from one direction, light comes from all over the sky. This scattered light fills in the shadow from all sides, making it very faint or disappearing entirely.

How do periscopes work? A periscope (used in submarines) uses two mirrors placed at angles. Light enters the top, reflects off the first mirror, travels down the tube, reflects off the second mirror, and reaches your eye. Since mirrors follow the law of reflection, the image appears upright. Periscopes let you see over obstacles (or above water in a submarine).

5 Common Mistakes Students Make

Mistake 1: Saying the Moon is a source of light.

The Moon is a non-luminous object. It has no fire, heat, or nuclear reaction to produce light. What we call “moonlight” is actually reflected sunlight. During a new moon (when the Moon is between the Earth and Sun), we can’t see the Moon because the sunlit side is facing away from us.

Mistake 2: Thinking translucent means the same as transparent.

Transparent = you can see clearly through it (clean glass window). Translucent = light passes through but is scattered, so the view is blurry (frosted glass, butter paper).

These are two different categories. Don’t mix them up in an exam.

Mistake 3: Saying that a pinhole camera image is just smaller, not inverted.

The pinhole camera image is both smaller AND inverted (upside down). This happens because light from the top of the object passes through the pinhole and hits the bottom of the screen, and vice versa. The inversion happens because light travels in straight lines and crosses at the pinhole.

Mistake 4: Saying shadows only form with sunlight.

Shadows form whenever any light source is blocked by an opaque object. A torch, a candle, a bulb — all produce shadows when something opaque is placed in their path. The light source just needs to be directional (coming from one direction).

Mistake 5: Thinking shadows are always the same size as the object.

Shadow size depends on the distance of the light source and the screen from the object. A small torch held very close to your hand will make a shadow much bigger than your actual hand. The Sun, being very far away, produces shadows closer to your actual size (especially at noon when it’s overhead).

Practice Questions

Q1. What is the difference between a luminous and a non-luminous object? Give two examples of each.

Luminous objects produce their own light. Examples: the Sun, a lit candle, a burning torch, a firefly, stars.

Non-luminous objects do not produce their own light. We see them because they reflect light from luminous sources. Examples: the Moon, a book, a chair, planets like Mars and Venus.

The key test: does the object produce light on its own? If yes — luminous. If it needs light from somewhere else to be visible — non-luminous.

Q2. Classify these materials as transparent, translucent, or opaque: (a) clear glass window, (b) butter paper, (c) wooden door, (d) clean water in a glass, (e) a thick curtain.

(a) Clear glass window — Transparent (light passes through clearly, you can see what’s on the other side)

(b) Butter paper — Translucent (light passes through but is scattered, you can’t see clearly through it)

(d) Clean water in a glass — Transparent (you can see clearly through it)

(e) A thick curtain — Opaque (blocks all light, used to darken a room)

Q3. What three things are needed for a shadow to form?

Three things are needed to form a shadow:

A source of light — light must be present (Sun, torch, candle, bulb). Without a light source, there is no light to block.
An opaque object — the object must block light. Transparent objects don’t form clear shadows because light passes through them.
A screen or surface — there must be a surface (wall, ground, paper) on which the shadow can fall and be seen.

All three are essential. Remove any one of them and no shadow forms.

Q4. Why does a pinhole camera produce an inverted (upside-down) image?

Because light travels in straight lines.

Light from the top of the object passes through the pinhole and continues in a straight line to the bottom of the screen. At the same time, light from the bottom of the object travels in a straight line through the pinhole and hits the top of the screen.

Since the light rays from the top and bottom of the object cross each other at the pinhole (like an X), the image that forms on the screen has the top and bottom switched — which means the image is upside down (inverted).

If light could bend around corners, the image would form the right way up. But because it travels only in straight lines, the image is always inverted in a pinhole camera.

Q5. What is lateral inversion? Give a real-life example where it is useful.

Lateral inversion is the swapping of left and right in a mirror image. When you look at yourself in a mirror, your right hand appears as the left hand of the image, and vice versa.

Real-life example: An ambulance has the word “AMBULANCE” written in mirror-reversed letters on its front/hood. When a driver ahead sees the ambulance in their rearview mirror, the lateral inversion of the mirror corrects the writing, and the driver reads “AMBULANCE” normally. This lets drivers identify the emergency vehicle quickly and move aside.

Q6. A girl holds her hand between a torch and the wall. When she moves the torch closer to her hand, what happens to the shadow? Explain why.

When the torch is moved closer to her hand, the shadow on the wall becomes larger.

This is because:

When the torch is far away, the light rays reaching the hand are nearly parallel (like sunlight). The shadow is approximately the same size as the hand.
When the torch is brought closer, the light rays spread out more widely around the hand at a bigger angle. This means the “cone” of blocked light is wider and produces a larger shadow on the wall.

The closer the light source, the larger the shadow. The farther the light source, the smaller (and more accurate to the object’s real size) the shadow becomes.

Q7. What is the difference between regular reflection and diffuse reflection?

Regular reflection (specular reflection): When light hits a smooth, polished surface (like a mirror or still water), all light rays reflect in the same direction. This produces a clear, sharp image. You can see yourself clearly in a mirror.

Diffuse reflection (irregular/scattered reflection): When light hits a rough surface (like a wall, paper, or road), the tiny bumps and uneven patches scatter light in many different directions. No clear image is formed, but the surface appears lit from many angles.

Diffuse reflection is why we can see non-shiny objects like walls, books, and faces — the scattered light reaches our eyes from many directions. It is also why a room can be lit without blinding reflected light from the walls.

Q8. Why does your shadow almost disappear on a cloudy day but is very sharp on a sunny day?

On a sunny day, sunlight comes from one direction — the Sun. Light rays are approximately parallel. When your body blocks these rays, a clear dark shadow forms on the ground on the opposite side.

On a cloudy day, clouds scatter sunlight in all directions. Instead of rays coming from just one direction, diffuse light comes from everywhere in the sky. This light fills in the shadow from all sides — light creeps in from the left, right, above, and everywhere. The shadow becomes very faint or disappears entirely because there is almost no region that is completely blocked from all light directions.

This is why professional photographers use cloudy days for outdoor portraits — the soft, scattered light eliminates harsh shadows and produces even lighting on faces.

Frequently Asked Questions

Why can’t we see in a completely dark room?

We see objects when light bounces off them and enters our eyes. In a completely dark room, there is no light at all. Nothing can reflect light that doesn’t exist. Even though the room still has all its furniture and objects, our eyes receive no light signals — so we see nothing. Our eyes detect light; they don’t produce it.

Why does a shadow always appear on the opposite side of the object from the light source?

Light travels in straight lines. When an opaque object is in its path, light cannot bend around it. The region directly behind the object (on the far side from the light) receives no light. This region of darkness is the shadow. Since light comes from one direction and travels straight, the shadow always falls on the opposite side.

Can a shadow be coloured?

Shadows themselves are dark (absence of light) and have no colour. However, shadows can look coloured if the light source is coloured, or if coloured light from another source illuminates the shadow area. In theatrical lighting with multiple coloured lights, shadows can appear in amazing colours because they receive light from some coloured sources but not others.

What is the difference between a shadow and a reflection?

A shadow forms when opaque objects block light — it is a region of darkness on a screen or surface. A reflection is a bounced image — it occurs when light bounces off a smooth surface back to your eyes. You see a shadow on the floor; you see your reflection in a mirror. Shadows are dark shapes; reflections are light images.

Why does water in a lake look like a mirror on a calm day but not on a windy day?

On a calm day, the water surface is flat and smooth — it acts as a regular reflective surface and produces clear mirror-like reflections. On a windy day, waves create a rough, bumpy surface. This causes diffuse reflection — light scatters in many directions — and no clear image can form. This is the same principle as regular vs diffuse reflection from smooth and rough surfaces.

Why is frosted glass used in bathroom windows?

Frosted glass is translucent — it allows light to pass through (so the bathroom is lit naturally) but scatters the light so you cannot see clearly through it. This gives privacy (people outside cannot see you clearly) while still letting daylight in. A clear transparent glass window would let in light but offer no privacy; a fully opaque wall would give privacy but block all light.