Luminous & Non-Luminous Objects

A luminous object produces its own light by burning, heating, or a chemical reaction. A non-luminous object does not produce light — it only becomes visible when light from a luminous source falls on it and is reflected into our eyes. The Sun, a candle flame, a glowing electric bulb, and fireflies are luminous. The Moon, a book, a mirror, and your hand are non-luminous. Light always travels in straight lines (rectilinear propagation), which explains why shadows are sharp-edged.

1. Ask: "Does this object produce its own light through burning, heat, or a biological process?" If yes, it is luminous.
2. If it only shines when another source illuminates it, it is non-luminous (even if it reflects very well, like a mirror).
3. To classify a material by how it interacts with light: shine a torch at it. If you can clearly see through it — transparent. If light passes but image is blurred — translucent. If no light passes — opaque.
4. To predict shadow size: a larger object or a source closer to the object gives a larger shadow on a screen placed behind.

Example 1: Is the Moon luminous?

• The Moon does not burn or generate energy.
• It reflects sunlight toward Earth.
• The Moon is non-luminous. We see it because it reflects the Sun's light.

Example 2: A student holds a frosted glass in front of a candle. Can she read a book through it?

• Frosted glass is translucent — it lets some light through but scatters it.
• She will see a glow but cannot read clearly through it.
• For clear reading she needs a transparent material.

• Thinking the Moon is luminous because it is bright at night — brightness depends on how much light is reflected, not on being a source.
• Confusing "shiny" with "luminous." A polished metal spoon is shiny but non-luminous.
• Believing light travels in curves around objects — it does not; this is why shadows form.

1. List two luminous and two non-luminous objects from your classroom.
2. Why is your shadow shorter at noon than in the morning?