Light: Shadows and | Class 7 Science Notes

11.1 Sources of Light

This section explains the different sources of light, distinguishing between natural and artificial sources. The Sun is identified as the primary natural source of light for Earth, emitting its own light that sustains life and illuminates the planet. Other natural luminous sources include stars, lightning, natural fire, and certain animals like fireflies that produce bioluminescence. The section also traces the history of artificial light sources, starting from the earliest human discovery of fire. Humans learned to create fire using various fuels such as animal fat, oil, wax, and gas, which served as artificial light sources before electricity. With technological advancement, electric light sources like bulbs and lamps have become the main means of lighting, offering efficiency and convenience. The concept of luminous and non-luminous objects is clarified: luminous objects emit their own light, while non-luminous objects do not but may reflect light, as in the case of the Moon. The section also highlights the environmental and economic benefits of LED lamps, which consume less power, are brighter, last longer, and reduce electricity bills and pollution. The government’s promotion of LED usage is noted, along with the importance of proper disposal or recycling of LED lamps to protect the environment.

📊 Diagram: Fig. 11.1 shows images of natural sources of light such as the Sun, stars, lightning, and fireflies. Fig. 11.2 depicts fire as an artificial light source using oil lamps and candles. Fig. 11.3 illustrates various electric light sources like bulbs and tube lights.

🔗 Connection: Prepares for the next section 'Does Light Travel in a Straight Line?' by establishing the nature of light sources.