Unit #3 Light and Optical Systems

Topic #1 – What is Light? Light is the form of energy you can see! Light is the form of energy you can see! The Sun is a natural light source (another natural source is fire) The Sun is a natural light source (another natural source is fire) The Sun is a star and all stars in the universe are sources of light The Sun is a star and all stars in the universe are sources of light Light radiates from stars (in all directions like spokes on a bicycle wheel) Light radiates from stars (in all directions like spokes on a bicycle wheel)

Energy such as light that travels by radiation is called radiant energy Energy such as light that travels by radiation is called radiant energy Because the Sun’s energy is not always available, humans developed light producing technologies Because the Sun’s energy is not always available, humans developed light producing technologies These sources of light are called artificial light sources (such as a light bulb) These sources of light are called artificial light sources (such as a light bulb)

Because light is a form of energy, when it is absorbed by a surface it can be transformed into several different forms of energy Because light is a form of energy, when it is absorbed by a surface it can be transformed into several different forms of energyEx. Light on a dark sweater producing thermal energy Light on a dark sweater producing thermal energy Solar cells transforming light into electricity Solar cells transforming light into electricity Trees absorbing light to produce sugars – chemical energy Trees absorbing light to produce sugars – chemical energy

Sources of Light What if there was no natural sources of light? What if there was no natural sources of light? Early civilization used torches, lanterns, candles Early civilization used torches, lanterns, candles Now we have light from lamps, computers, televisions and other new- fangled gadgets Now we have light from lamps, computers, televisions and other new- fangled gadgets Here are some sources of light…. Here are some sources of light….

Incandescent Sources An object can be heated to such a high temperature that it emits visible light An object can be heated to such a high temperature that it emits visible light Such an object is called an incandescent source of light Such an object is called an incandescent source of light The emission of visible light by a hot object is called incandescence The emission of visible light by a hot object is called incandescence Example: filament light bulbs Example: filament light bulbs Tidbit – almost 95% of the energy given off by an incandescent light bulb is released as heat! Tidbit – almost 95% of the energy given off by an incandescent light bulb is released as heat!

Fluorescent Sources When you stand under a “black light”, you may notice that your white clothes glow! When you stand under a “black light”, you may notice that your white clothes glow! In this process, high energy, ultraviolet light is absorbed by the particles in the fabric In this process, high energy, ultraviolet light is absorbed by the particles in the fabric The particles in the fabric then emits some of this energy as light you can see. The particles in the fabric then emits some of this energy as light you can see. This glow is called fluorescence This glow is called fluorescence

A fluorescence light bulb uses this energy transformation A fluorescence light bulb uses this energy transformation Electricity is run into the ends of the bulb which is filled with mercury vapor Electricity is run into the ends of the bulb which is filled with mercury vapor The mercury vapor emits ultraviolet radiation which is absorbed by the phospor coating on the inside of the bulb. The mercury vapor emits ultraviolet radiation which is absorbed by the phospor coating on the inside of the bulb. This causes the coating to glow and produce visible light This causes the coating to glow and produce visible light Mercury vapor inside the tube is toxic! Mercury vapor inside the tube is toxic!

Phosphorescent Sources Phosporescent sources of light are similar to fluorescent sources Phosporescent sources of light are similar to fluorescent sources Light is absorbed by certain particles that store the energy and release it later as visible light Light is absorbed by certain particles that store the energy and release it later as visible light The persistent emission of light following exposure to and removal of a source of radiation is called phosphorescence The persistent emission of light following exposure to and removal of a source of radiation is called phosphorescence

The main difference between a fluorescent source and a phosphorescent source is that the particles in the fluorescent source release their light energy immediately The main difference between a fluorescent source and a phosphorescent source is that the particles in the fluorescent source release their light energy immediately Examples: Examples: Star and moon stickers you can put on your ceiling Star and moon stickers you can put on your ceiling The dials of older watches or clocks The dials of older watches or clocks

Chemoluminescent Sources Light can also result from the energy released in chemical reactions Light can also result from the energy released in chemical reactions The chemical reaction produces energetic particles that give off visible light energy The chemical reaction produces energetic particles that give off visible light energy This process is chemoluminescence This process is chemoluminescence Examples: Examples: Glow sticks can be broken to mix two chemicals that react and release light Glow sticks can be broken to mix two chemicals that react and release light

Bioluminescent Sources If you were moving through the darkest depths of the ocean, you may be surprised to see glowing creatures If you were moving through the darkest depths of the ocean, you may be surprised to see glowing creatures They rely on chemical reactions within their bodies to provide energy for light They rely on chemical reactions within their bodies to provide energy for light This special type of light produced in living creature is called bioluminescence This special type of light produced in living creature is called bioluminescence Examples: deep sea fish, plankton, jellyfish, fireflies Examples: deep sea fish, plankton, jellyfish, fireflies

Other Facts All objects that emit light are said to be luminous All objects that emit light are said to be luminous So how can you see non-luminous objects that do not emit light? So how can you see non-luminous objects that do not emit light? We’ll find out later on… enough for today We’ll find out later on… enough for today Or is it………………? Or is it………………?