[Visible*] Light is a type of electromagnetic radiation
within a certain portion of the electromagnetic spectrum.
Electromagnetic radiation (EM radiation or EMR)
(consists of electromagnetic waves) is the radiant energy
released by certain electromagnetic processes. It is a kind
of radiation including
visible light, radio waves, gamma rays, and X-rays,
in which electric and magnetic fields vary simultaneously.
* which is visible to the human eye and is responsible for
the sense of sight.
The electromagnetic waves that compose electromagnetic
radiation can be imagined as a self-propagating transverse
oscillating wave of electric and magnetic fields. This
diagram shows a plane linearly polarized EMR wave
propagating from left to right. The electric field is in a
vertical plane and the magnetic field in a horizontal plane.
The electric and magnetic fields in EMR waves are always
in phase and at 90 degrees to each other.
animation shows a
left to right. Note
that the electric
fields in such a
wave are in-phase
with each other,
The colors that make up white light are called visible
Color Wavelength (nm)
Red 780 – 622 = 158 nm
Orange 622 – 597 = 25 nm
Yellow 597 – 577 = 20 nm
Green 577 - 492
Blue 492 - 455
Violet 455 - 390
• Infrared radiation (IR) is used in some television
controls, night vision photography, sea surface temp
• Ultraviolet radiation (UV) that seeps through the
atmosphere is known to cause skin cancer. Frogs are
sensitive to UV so they are monitored to see the
presence of holes in the Ozone.
The relative wavelengths of the electromagnetic waves of three
different colors of light (red, green, and blue) with a distance scale in
micrometers (1 meter is 1,000,000 micrometer) along the x-axis.
The main source of light on Earth is the Sun.
About 49 % of the electromagnetic waves emitted by the
Sun are infrared waves, about 43 % are visible light, and
about 7 % are ultraviolet waves.
Some ancient philosophers (like plato and
pythagoras) believed that light traveled
from our eyes to the objects
we look at, rather than
from the objects
Abu Ali Hasan Ibn Al-Haytham, c. 965 – c. 1040 CE
Light and Plant Growth
What kind of materials does light pass through?
You will watch a video shows that our reality doesn't look the same in a different
spectrum of light. Things which are opaque in visible light are sometimes totally
transparent in the (near) infrared light. In the video a Delamax 950 nanometer
filter is used. The human eye is sensitive from about 390 to 700 nm.
Transparency in IR spectrum (950nm)