What Do You See?
Human vision is dependent on light. We can only see if the light-sensitive cells on our retina at the back of our eyes get triggered by light entering the eye. As a result, we can only see objects that either are illuminated and reflect light back into our eyes, or objects that emit light. Any object that is in complete darkness is not visible to the human eye. In this lesson plan, students will place different objects inside a box and view them under different light conditions. By doing so, students will realize that our ability to see an object clearly is light-dependent. The more light that is present, the more details of an object can be seen.
Remote learning: This lesson plan can be conducted remotely. The Engage section of the lesson can be done over a video call, then students can work individually and independently during the Explore section, using the student worksheet as guide. A set of materials can be prepared in advance or students can use materials found around the house. And adult will be needed to assist with the preparation of the box. End the lesson with discussion over a video call during the Reflect section.
- Conduct an experiment that shows that light is needed to see objects.
- Understand the difference between an illuminated and a luminous object.
- Explain, with evidence, that some objects can be seen at night and some cannot.
NGSS AlignmentThis lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
- 1-PS4-2. Make observations to construct an evidence-based account that objects in darkness can be seen only when illuminated.
|Science & Engineering Practices||Disciplinary Core Ideas||Crosscutting Concepts|
|Science & Engineering Practices||Constructing Explanations and Designing Solutions.
Make observations (firsthand or from media) to construct an evidence-based account for natural phenomena.
Analyzing and Interpreting Data. Record information (observations, thoughts, and ideas).
Use observations (firsthand or from media) to describe patterns and/or relationships in the natural and designed world(s) in order to answer scientific questions and solve problems.
|Disciplinary Core Ideas||PS4.B: Electromagnetic Radiation.
Objects can be seen if light is available to illuminate them or if they give off their own light.
||Crosscutting Concepts||Cause and Effect.
Simple tests can be designed to gather evidence to support or refute student ideas about causes.
For each student group of 3:
- Cardboard box (shoe box or mailing box)
- Black tape
- Sharpened pencil
- Various objects that fit into the box, some of them luminous, such as a glow stick, light-up toys, etc.
- Optional: Flashlight
For the teacher:
- Utility knife or scissors
- Double-sided tape
Background Information for TeachersThis section contains a quick review for teachers of the science and concepts covered in this lesson.
Our eyes are complex organs that allow us to see objects, colors, and everything that happens around us. To be able to see, however, we need light. Sight begins when light enters the eye. Usually what we see is light that reflects from objects and then enters our eyes. The light triggers light-sensitive cells on the retina in the back of our eyes and as a result, signals are sent through the optic nerve to the brain (Figure 1). The brain makes sense of the signals, giving us the experience of seeing. The retina of a human eye has two types of light-sensitive cells: cones and rods. The rods are extremely efficient: a small amount of light can trigger them. They are responsible for our night vision. They detect lines, contrast, and movement, but cannot distinguish color. The cones are responsible for color vision, but these need plenty of light to get activated. That is why in dim light conditions, you recognize objects, but fail to detect their color.
Figure 1. Schematic diagram of the eye anatomy showing how light enters the eye.
The pupil is the opening in the middle of the eye that allows light to enter the eye. Humans have round pupils. They appear black because light almost never escapes through them. The colored part around the pupil, called the iris, adjusts the size of the pupil. Its main function is to regulate the amount of light that enters the eye. It is connected to a muscle that allows the pupil to open and close in a circular motion. In dim light, the pupils dilate (open wider) so more light can enter. Switch to bright light, and the pupils automatically constrict (Figure 2). This constriction is the result of a small fraction of the nerve signal generated in the back of the eye triggering the muscles in the iris. As some nerve connections cross over to the other eye, both pupils constrict or dilate simultaneously.
Figure 2. The pupil can dilate or constrict, depending on the surrounding light conditions.
In this lesson plan, students will explore their vision under varying light conditions. As they look at different objects in a space with no light and with light, they will quickly realize that objects in darkness can only be seen when illuminated or when the object emits its own light. The more that light shines onto the object, the more details of the object can be detected by our eyes.