Only When the Light Falls On It
A 50-minute Grade 1 lesson on building an evidence-based account that objects can be seen only when they are lit.
Only When the Light Falls On It is a free 50-minute Grade 1 science lesson plan for Common Core standard 1-PS4-2 — show that you can only see an object when light falls on it. It is timed across 5 sections, gives the exact wording to use where the wording carries the mathematics, names 3 misconceptions with the teaching move that addresses each, and ends with an exit ticket and a printable worksheet with its answer key.
- Grade:
- Grade 1
- Length:
- 50 minutes
- Standard:
- 1-PS4-2
Grade 1 · Physical Science
1-PS4-2
Make observations to construct an evidence-based account that objects can be seen only when illuminated.
Objective
Students will be able to explain, from a test, why an object cannot be seen in the dark.
Students are successful when they can
- Reports what was seen with and without light.
- Explains the difference by the light, not by the object.
- Says the object did not change.
What you need
- A shoebox with a lid, a viewing hole and a small torch inside
- A toy that stays in the box throughout
- The printable practice sheet linked at the end of this plan
The lesson
Warm-up — what is in the box?
5 min- Pass the closed box round and ask each pupil to look through the hole.
- Ask what they can see. Nothing.
Teach — the toy never moved
13 min- Switch on the torch inside without opening the box. Pass it round again.
- Ask what changed. Only the light.
- Ask what did not change. The toy, which never moved.
- Take the lid off with the torch off. The toy is visible in daylight.
- Say the account in full: you see an object when light falls on it and reaches your eye.
- Head off the wrong version: the toy is not glowing, the light is bouncing off it.
“The toy did not change. What did?”
Investigate — three boxes
17 min- Groups make their own box with a hole, a lid and an object inside.
- They record what is seen with the lid on, lid on with torch, and lid off.
- They swap boxes and predict before looking.
- They write one sentence saying why the object could not be seen at first.
Independent practice
12 min- Students complete the 'Only When the Light Falls On It' page.
- Check answers say light falls on it, not that the object lights up.
Close
3 min- Ask why we can see the moon at night.
What goes wrong, and why
Each of these is a reasoning error rather than carelessness. The fix addresses the reasoning.
Thinks objects give off their own light.
Why: Some things do, so all might.
Fix: Take the torch out of the box. The toy stops being visible at once.
Thinks eyes send out something to see with.
Why: Seeing feels active.
Fix: Shut the lid and stare hard. Looking harder changes nothing.
Says the object changed in the dark.
Why: It looked different, so it must be different.
Fix: Point at the toy in the light. It never moved and never changed.
If they are not there yet
- Use the teacher's box rather than building one.
- Two conditions rather than three.
If they finish early
- Explain why a cat's eyes seem to shine in headlights.
- Make an object visible without opening the box or using the torch.
- Say what would happen with a very dim torch.
Exit ticket
A toy in a closed dark box cannot be seen. The toy has not moved. Why can you not see it?
What to look for: No light falls on it and reaches your eye. An answer that the toy changed means the it-never-moved point needs another run.
Printable practice for 1-PS4-2
Free to print and copy, answer key included. Each sheet can generate a fresh set of problems for a retake.
- Only When the Light Falls On ItCircle the best answer.
Questions about Only When the Light Falls On It
How long does the Only When the Light Falls On It lesson take?
50 minutes, split across 5 timed sections: warm-up 5 min, teach 13 min, investigate 17 min, independent practice 12 min, close 3 min. The minutes are stated per section and add up to the stated length, so the plan can be cut or extended at a section boundary rather than abandoned halfway.
Which standard does Only When the Light Falls On It teach?
1-PS4-2 — 1-PS4-2, Physical Science for Grade 1: “Make observations to construct an evidence-based account that objects can be seen only when illuminated.” In plain terms, show that you can only see an object when light falls on it.
What do I need to teach this lesson?
A shoebox with a lid, a viewing hole and a small torch inside, a toy that stays in the box throughout and the printable practice sheet linked at the end of this plan. Everything listed is either ordinary classroom equipment or a free printable from this site — there is nothing to buy and nothing to prepare beyond photocopying.
What mistakes should I expect in this lesson?
Three, each a reasoning error rather than carelessness: thinks objects give off their own light; thinks eyes send out something to see with and says the object changed in the dark. The plan gives the thinking behind each one and the teaching move that addresses the thinking rather than the symptom.
How do I know whether the lesson worked?
The exit ticket asks: “A toy in a closed dark box cannot be seen. The toy has not moved. Why can you not see it?.” No light falls on it and reaches your eye. An answer that the toy changed means the it-never-moved point needs another run. That tells you whether the class needs a reteach or a thirty-second conversation before you plan tomorrow.
Is there a worksheet to go with Only When the Light Falls On It?
Yes — 1 printable 1-PS4-2 worksheet, linked at the end of the plan and free like the rest of the site. Each one comes with an answer key and 25 versions, so the practice after the lesson can be a different paper on every desk.
Is Only When the Light Falls On It free to use?
Yes. The plan, its printables and their answer keys are free to read, print and photocopy for your own class, with no account and no email capture. It was last reviewed on 8 September 2026. Please do not resell it or republish it as your own.
Last reviewed 2026-09-08. Aligned to 1-PS4-2 of the Next Generation Science Standards.