Light: a path from the sky to a picture

Find the source

Look around the room and identify a lamp or a window providing light. Point to a page receiving it, then indicate where a reader sits. Draw three symbols and connect them in order.

Cover part of the page with an opaque card without touching a hot lamp. The darker area helps you notice that the card blocks a path. Do not shine lights into anyone's eyes.

Change one condition

Keep a cup, paper and your seat in the same places. Move a cool LED lamp to one side and then the other. Sketch the cup's bright and dark areas and label what you changed.

If you also change the cup, paper and viewing position, it becomes harder to explain the difference. A useful comparison keeps the question small enough to investigate.

Suppose the cup stays at a marked spot and the lamp moves from left to right. Compare the side facing the lamp, the shadow and the background separately. A page with those three observations gives a clearer explanation than saying only that the picture changed.

Compare light with pigment

A screen creates colour using emitted light, whereas painted paper is viewed through light reflected from pigments. A colour-mixing rule needs a named medium; a rule for paint cannot automatically be transferred to a screen.

Design two separate record sheets, one for a drawing application and one for paints. Label the materials and conditions before comparing results. A similar colour name does not guarantee the same physical process.

Choose a prediction for each medium before trying it. Describe the actual software setting or pigment materials rather than assuming that a shared colour name guarantees an identical mixture.

Repeat a small comparison under similar viewing conditions. A difference between trials may come from unequal pigment amounts, screen settings or illumination, so list these possibilities before treating one result as a general law.

Move from ray model to spectrum

A ray diagram describes directions of travel. A spectrum describes how light is distributed across wavelengths. These representations answer different questions and may be needed together to explain an observation.

Choose a claim such as why one surface looks different under two lamps. List the information your simple diagram lacks before adding a more detailed representation. More detail is useful only when it helps answer the question.

A spectrum describes the distribution of light across wavelengths, but a displayed spectrum also depends on calibration and plotting choices. Ask what quantity is represented on each axis and whether the scale supports a qualitative comparison or a numerical claim.

For a painting under two lamps, separate illumination, surface response and observation conditions. A ray model can describe a route without specifying the spectral composition that reaches the eye. Identify the additional information required and avoid presenting the most detailed picture as automatically the best explanation.

Evaluate an image-making process

Consider a photograph of your lamp-and-cup setup. Brightness in the image depends on the scene and on camera settings. Record exposure changes instead of attributing every difference to the object.

Compare a fixed-camera series with an automatically adjusted series. Discuss what each can support, and where direct comparison becomes uncertain. This is a proposed classroom inquiry, not a completed experiment.

Question and hypothesis: will a fixed scene photographed with automatic exposure appear more constant in brightness than a series with fixed settings when the lamp changes? Treat this as a testable proposal, not a promised result.

Method and data: use an indoor object, mark source positions, record available settings and preserve every trial. Compare the same image region using a stated procedure, while noting that processed pixel values are not automatically calibrated physical measurements. Include a simple decision rule: if the camera settings changed between files, do not use raw image brightness alone as evidence that the surface reflected more light. Mark that comparison as confounded and identify what a new fixed-setting trial would need.

Limitations: camera processing, reflections and changing ambient light may prevent a clean comparison. State which factor you could control in a repeat and which conclusion remains unsupported by the present images. Discuss whether your chosen image region contains a reflection highlight or a shaded area. Two regions can respond differently, so selecting the region after seeing the results could make the argument misleading.