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Light Energy

How light travels in straight lines from a source, reflects off surfaces so we can see objects, and forms shadows when something blocks its path.

⏱ 10 min · 🎯 4 things to master

A flat-vector scene showing a bright sun and an electric lamp sending straight yellow ray lines toward a shiny mirror, with the rays bouncing off at equal angles — on a soft off-white background in IllumiTutor navy and amber, no text.

Pick up your pencil case and look at it. You can see it — but your pencil case does not glow. So how do your eyes know it is there? The answer is light. A light source somewhere in the room sends out light rays. Those rays hit your pencil case, bounce off, and travel to your eyes. Without a light source, you cannot see anything at all. In this note you will discover how light moves, why mirrors are special, and the exact words your PSLE marker is looking for.

Parents: each section has a short interactive step — let your child predict before they tap "reveal" or "fire". Saying the keyword out loud is how it sticks. The whole note takes about 15 minutes to try together.

By the end you will be able to explain: how light travels, the difference between a light source and an object we see by reflected light, how reflection works, and when shadows form. Let's start with the most surprising fact.

Light Travels in Straight Lines

Hold a torch in a dark room and switch it on. The beam goes straight. It does not curve around your furniture or sneak through a wall — it goes in a perfectly straight line until it hits something. This is always true: always travels in straight lines.

You can prove it yourself. Line up three cards, each with a small hole in the centre, one behind the other. When all three holes are in a line, you can see the light through them. Tilt just one card — the light disappears, because the path is no longer straight. Light cannot bend around the hole.

Here is the science in one sentence that your marker loves: light travels in straight lines.

🤔 Predict first: If you put a solid book between a torch and a wall, what shape does the dark patch on the wall have?

Light Sources vs Objects We See by Reflected Light

Flick off every light in your room at midnight — total darkness. Now switch on a lamp. You can instantly see the lamp (it glows) and you can also see your desk, your books, your chair. But those objects are not glowing by themselves. So why can you see them?

A produces light on its own. The sun is a light source; it burns and gives out light. A lamp is a light source; electricity makes the bulb glow.

Most objects around you are not light sources. Your desk, your book, your face — none of these make their own light. You can see them because light from a source hits them, and some of that light bounces off the surface and travels to your eyes. We say you see them by .

🤔 Predict first: The moon looks very bright at night. Is the moon a light source, or do we see it by reflected light?

Reflection: Light Bounces Off Surfaces

When light hits a smooth, shiny surface — like a mirror or still water — it bounces off in a very orderly way. This is called .

Here is the rule that makes mirrors so useful: the angle light hits a mirror equals the angle it bounces off. Scientists call these the angle of incidence and the angle of reflection. For the PSLE you just need to know: the bounce angle equals the hit angle. That is why you can aim a light ray at a mirror and predict exactly where it will go after it bounces.

Because of this rule, you can steer a beam of light by changing the mirror's angle. Tilt the mirror a little and the bounced ray goes somewhere completely different. Try it in the experiment below.

Aim the light ray at the target

Predict first: If light hits a mirror at a slant, which way does it bounce?

Shadows: What Happens When Light Is Blocked

When an opaque object stands in the path of light, the light cannot pass through. A dark area forms on the other side — a shadow. Because light travels in straight lines, the shadow has a clear, sharp edge and matches the outline of the object.

This note is focused on light sources and reflection, and the companion note Properties of Materials goes deeper into transparent, translucent, and opaque objects and their shadows. The key link: shadows only form because light travels in straight lines — if light could bend around objects, there would be no shadows at all.

🤔 Predict first: A student holds a transparent glass in front of a lamp. Will there be a shadow on the wall?

Watch out — these are easily mixed up

Quick recap

🎯 Mastery check

Answer all 8 — your progress is saved on this device.

  1. Why can you see your school bag even though it does not glow?

  2. Which of these is a light source?

  3. A student uses three cards with holes to test whether light bends. When she tilts the middle card, the light disappears. What does this show?

  4. You shine a torch at a mirror set at a low angle. The reflected ray goes downward. What happens to the reflected ray if you tilt the mirror upward?

  5. The moon looks very bright on a clear night. Which statement about the moon is correct?

  6. A student places an opaque box and a transparent glass in front of a lamp, one at a time. Which object casts a clear dark shadow, and why?

  7. Your friend says "light reflects off a mirror and then curves toward the ceiling." Is she correct?

  8. You want to light up a dark corner in your bedroom by bouncing torchlight off a mirror on the wall. This is possible because of which property of light?