4-PS4-2: How Light Lets Us See
Also called NGSS 4-PS4-2 · Topic: Structure, Function, and Information Processing · Physical Science
The Official Wording
Develop a model to describe that light reflecting from objects and entering the eye allows objects to be seen.
Assessment boundary: Assessment does not include knowledge of specific colors reflected and seen, the cellular mechanisms of vision, or how the retina works.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What 4-PS4-2 Means in Plain English
Fourth graders build a model, often a labeled diagram with arrows, to show how we see things. Light from a source like the Sun or a lamp hits an object, bounces off it, and travels into our eyes. No light reaching the eye means nothing is seen.
Students do not study which colors bounce off or how the eye and brain turn light into sight. It builds on first grade work showing objects are seen only when lit (1-PS4-2) and pairs with senses and the brain (4-LS1-2).
4-PS4-2 I Can Statements
- I can draw arrows showing the path light takes so I can see.
- I can explain why I cannot see objects in total darkness.
- I can use a model to show light bouncing off objects.
4-PS4-2 Worked Example
A model a class can build from a shoebox to test what the eye needs in order to see.
Can you see a toy inside a closed box if no light gets in?
Set It Up: A shoebox with its lid taped on, a small toy dinosaur glued inside, a peephole in one end, a flap cut in the lid, and a flashlight.
- Keep the flap closed and look through the peephole.All black, no toy
- Open the flap a little to let room light in.Toy is dim but visible
- Shine the flashlight through the flap onto the toy.Toy is bright and clear
- Draw the path: an arrow from the flashlight to the toy, then from the toy to the eye.Two arrows on the diagram
The toy could be seen only when light entered the box, and more light made it easier to see.
Why it works: We see an object when light bounces off it and travels into our eyes, so with no light there is nothing to bounce.
Common Mistakes with 4-PS4-2
Arrows coming out of the eye
A drawing with lines going from the eye to the toy
Try this: Light travels into the eye, not out of it. Draw arrows from the light source to the object, then to the eye.
Thinking eyes adjust to total darkness
“If you wait long enough you'll see in the dark.”
Try this: Eyes adjust to dim light, but in a fully dark box nothing reaches them, so no amount of waiting lets you see.
Thinking only shiny things reflect
“Mirrors bounce light, but my shirt doesn't.”
Try this: Most objects bounce some light. That is how you see a dull shirt at all. Shiny surfaces bounce it back in a neat, mirror-like way.
Where 4-PS4-2 Fits
Practice 4-PS4-2
Quick Check
- Why can't you see your hand in a room with no light at all?
- Which way should the arrows point in a seeing diagram?
- Is the Moon a light source?