Grade 10 Academic Science
How is light produced?
Science Perspectives 10 Section 11.2 Pages 470-476
Laser – A Special Type of Light
Science Perspectives 10 Section 11.3 477-478
We typically think that light only comes from sources such as the Sun, a light bulb or a fire. Yet, light
enters our eyes from all objects you see. I can see you only if light from you enters my eyes. What is the
difference between light coming from a source such as the Sun and light coming from you?
Task

Use your textbook to complete the following information
We see objects because _________________ is coming from them.
Objects which produce their own light are called __________________________.
 Examples
Most objects are visible because they reflect light. They are called ___________________________.
 Examples
Light is produced in several ways.
Method of Production
Explanation
Examples
Method of Production
Explanation
Examples
Laser
Light Amplification by Stimulated Emission of Radiation
Each of the light sources in the previous section emits electromagnetic radiation of many different
energies (POLYCHROMATIC) AND in all directions. Laser is different.
Laser properties
 Laser emits electromagnetic waves of exactly the same energy level. The visible spectrum is
white light composed of all colours. Laser light is only one colour (MONOCHROMATIC or one
wavelength). It can be blue or it can be red, but it is not both at the same time. Thus, it only emits
a narrow range of wavelengths. If it is red, the laser is only emitting the range of red wavelengths.

Laser light can occur in the invisible parts of the Electromagnetic Spectrum (e.g., infrared light or
ultraviolet light). This type of laser is invisible to the naked human eye.

Laser light is HIGHLY DIRECTIONAL and HIGHLY FOCUSED (COHERENT). Why? The
photons of laser light are all in the same wavelength. Thus, the photons must be traveling at the
same speed. As well, the photons are traveling in the same direction (i.e., there is no
“competition” between photons); rather, the light travels in unison. These similarity features
makes laser light focused and intense.
Why is laser light dangerous to the human light? You know the properties of laser light. Now,
think of the structure and functioning of the human eye. What wavelengths of light can the human
eye detect? What is the energy level of the visible spectrum?
Incandescence versus Fluorescence
The Sun and other objects that produce and emit light are LUMINOUS.
INCANDESCENCE is the production of light using heat. In an incandescent light bulb, electricity passes
through a thin, coiled wire inside the bulb and the wire heats up. It glows. At the same time, the thermal
energy produced by the wire is given off as heat (…explains why the light bulb becomes hot…).
 NOTE: Only a small portion of the electricity passing through the wire is converted to visible light.
Most of the electricity is wasted as thermal energy. In other words, the incandescent light bulb in
very inefficient in producing visible light.
FLUORESCENCE uses a substance that absorbs high-energy ultraviolet (UV) radiation and converts that
energy to visible light. A fluorescent light bulb is a gas tube filled with a mixture of MERCURY and
ARGON GAS. The inside of the glass tube is coated with a fluorescent material that absorbs ultraviolet
light. When the light is turned on, electricity flows through the mercury-argon mixture and excites the
mercury atoms. As the mercury returns to a non-excited state, it releases photons of invisible UV light.
The coating on the tube absorbs the UV and converts it to visible light.
 NOTE: A fluorescent light produces much less thermal energy that the equivalent sized
incandescent light bulb. As well, it uses less electricity to produce the same amount of light.
Thus, the fluorescent light bulb is energy efficient.
 NOTE: An environmental drawback to the fluorescent light bulb is the MERCURY.
TASK
The big debate is the cost. The fluorescent light is expensive; yet, it is advertised as an energy-saving
and cost-saving device. Does the fluorescent light save you money? Let us compare.
Incandescent versus Fluorescent
Type
Watts
(W)
Cost
per
bulb
Operating
Life
Electricity
Rate
(hours)
($/kWh)
($)
Incandescent
60
0.50
1,000
0.09
Fluorescent
15
3.5
10,000
0.09
Number
of Light
Bulbs
Saved
Dollar
Savings
in Light
Bulbs
Cost
after
one
hour
Cost
after
10,000
hours
($)
($)
($)
NOTE: By using a fluorescent light bulb, you reduce greenhouse gas emission from by power plants by
313 kg of carbon dioxide
Non-luminous Objects
Objects that DO NOT produce their own light are non-luminous. The moon is non-luminous. Nonluminous objects may appear bright because they reflect light.
Can an object be non-luminous and luminous?
ANSWER
Incandescent versus Fluorescent
Type
Watts
(W)
Cost
per
bulb
Operating
Life
Electricity
Rate
(hours)
($/kWh)
($)
Number
of Light
Bulbs
Saved
Dollar
Savings
in Light
Bulbs
Cost
after
one
hour
Cost
after
10,000
hours
($)
($)
($)
Incandescent
60
0.50
1,000
0.09
--
--
0.5054
59.50
Fluorescent
15
3.5
10,000
0.09
10
1.50
3.5014
20.50