1. Science 8: Unit C – Light and Optical Systems Topic 1: What is Light?

2. I. Light is a form of Radiant Energy Light is a form of energy that we can see. Light travels in waves. Light, in fact is a kind of radiation. This means that light rays can travel across empty space. Other kinds of waves like sound waves need some kind of material to travel through. That’s why an astronaut cannot hear the explosion of his spaceship, but can see it explode. Light travels in straight lines. We call these straight lines ‘rays’. The more rays there are in an area, the brighter the light will look.

3. I. Light is a form of Radiant Energy Cont’d Since light is a form of energy, different light sources have more or less energy than others. We measure light energy by its intensity. The brighter the light, the more energy it has. Light rays can be reflected, diffracted, refracted, or absorbed by an object. Black objects tend to absorb most light that hits them and white objects tend to reflect most light rays that hit them.

4. II. Light Sources Light can either come from natural (eg. sun, stars, animals) or artificial sources (eg. light bulbs, TV screens). Here are a few types of artificial light sources.

5. 1. Incandescent Light Traditional light bulbs which use a thin metal wire to conduct electricity. The electrical current causes the wire to glow white hot producing light. An advantage of these bulbs is that they’re cheap, a disadvantage is that they are very inefficient losing 90% of its energy to heat.

6. 2. Fluorescent Light Fluorescent Light bulbs. An electrical current is run into a tube full of mercury vapor. The mercury atoms become excited and produce UV radiation. The UV radiation reaches phosphor powder on the tube which also gets energized/excited and releases light energy that we see. An advantage of fluorescent lights is that they are much more efficient than incandescent lights. A disadvantage is that they contain poisonous mercury vapor.

7. 3. Phosphorescent Light Sources Glow in the dark toys/stickers/tools. Similar to fluorescence except that light energy is stored over time and then released in the dark after the light source has been removed. This process of gradual release of light is called phosphorescence.

8. 4. Chemiluminscent Sources Glow Sticks. Chemical reactions produce energy in the form of light. So stored chemical energy produces light energy. In a glow stick a barrier separates the two reactants. When the barrier is broken the reactants mix producing the light energy.

9. 5. Bioluminescent Sources Deep Sea Creatures. Biochemical reactions in certain living things produce light energy. This is especially helpful in areas where there is no light from the sun such as the ocean floor.

10. III. The Cost of Lighting Light energy in Alberta is provided by your local power company (Epcor, Enmax) and is part of your power bill. The formula to find out how much the light will cost is: Cost (in ¢ or $) = Power of bulb (in kW) * Time being used (in h) * Price of Power (in ¢ or $)

11. IV. Transparent, Translucent, and Opaque Objects Transparent objects allow light rays to pass through without getting bent. You see a clear image across a transparent object. Translucent objects allow only some light rays to pass through and most of these are bent. You can see light, but you can’t see a clear image. Opaque objects absorb or reflect all light rays allowing none of them to pass through. You see no light or images.