Transcript No Slide Title

Luminous Flux
• The rate at which light is emitted from a
luminous body.
• Symbol: P
• Units: Lumen Abbreviation: lm
Illuminance
• The total amount of light that falls on a
surface.
• Symbol: E
• Unit: Lux
Abbreviation: lx
Distance and Illumination
• As a light source recedes from the object of
illumination the intensity of the illumination
decreases by an inverse squared
relationship.
• To illuminate a surface you can do either
– increase the luminous flux (brighter light
source)
– more the object closer
P
E
2
4r
Luminous Intensity
Luminous intensity is related to the brightness
of a light source (the amplitude of the
waves) and is simply another way of
defining the luminous flux from a point
source.
P
Symbol: I
I
4

Unit: Candela, cd
P
I
E 
 2
2
4 r
r
Color
• White Light: A combination of all the other
colors/wavelengths of light in a single beam.
• Color by Reflection: As we know, opaque
objects reflect light that hits their surfaces and
does not allow light to pass through. When
light hits a surface, the characteristics of that
surface at the the atomic level determine what
light will be absorbed and what color light will
be reflected.
• This phenomena is very similar to the emission
of spectral lines from excited atoms
• An orange appears orange because when
presented under white light, the skin
absorbs the white light (all colors) but reemits or reflects the part of the light in the
orange wavelength.
• An object that appears white reflects all
colors.
• An object that appears black absorbs all
colors and re-emits no light.
Complimentary Colors
• On the light color wheel, the complimentary
color of each primary color is located
directly opposite of the primary color.
• Combining this complimentary, secondary
color (comprised of the other 2 primary
colors) with the first primary color results
in what color light?
• When the compliment of one color is
incident upon a surface of that color, no
light is reflected.
• A good primer on various aspects of light,
color and how the human eye works
– http://www.d.umn.edu/~mharvey/th1501color.html
Primary
Complementary
Makes white with:
(single secondary color that makes white
with primary complement)
Red
Cyan
Blue + Green
Green
Magenta
Red + Blue
Blue
Yellow
Red + Green
Color
Red
Red
Green
Blue
Cyan
Magenta
Yellow
More red
Yellow
Magenta
White
Reddish
Magenta
Reddish
Yellow
Green
Yellow
More green
Cyan
Greenish
Cyan
White
Greenish
Yellow
Blue
Magenta
Cyan
More blue
Bluish Cyan
Bluish
Magenta
White
Cyan
White
Greenish Cyan
Bluish Cyan
More cyan
White*
White*
Magenta
Reddish
Magenta
White
Bluish
Magenta
White*
More
Magenta
White*
Yellow
Reddish Yellow
Greenish Yellow
White
White*
White*
More Yellow
*Whites indicated with an asterisk (*) will represent all colors present but may be strongly hued whichever color is most present.
Which is all pretty much summed up here:
Black and White
• Lots of confusion surrounds these “colors”
and what they mean. As far as light is
concerned:
– Black = absence of color, no light present, no
light reflected
– White = all colors present to some degree*,
reflects all colors
*Whites can be hued where a color, or colors, are
more dominant than other colors.
Painting and Pigment
• Far from an expert on artistry, the chemistry and physics
behind light and the way that it reacts with pigment to
produce color by reflection is fairly straightforward. To
sum up: Your first grade teacher was wrong!
– Truthfully he/she was just oversimplifying to the point of being
wrong, and possibly did not know better, so we won’t hold this
against them.
– Red, yellow and blue are NOT the Primary Colors of light,
pigmentation or anything.
– The secondary colors of light (Magenta, Yellow and Cyan) are, in
fact, the primary colors of painting/pigment due to the way they
reflect and absorb the primary light colors
– You might say that the secondary colors of light are the primary
colors of pigments and vice-versa.
Here’s a nice little graphic to help you out
(courtesy of the website linked earlier):
Color by transmission
• White light can be “filtered” such that only
a particular frequency of that light is
allowed to get through.
• For example, placing a pane of blue or red
glass in front of a flashlight would make the
beam appear to be blue or red respectively.
• The result, when this light is used to
illuminate objects, is that the object will
only appear in the hues of the color
transmitted upon reflection of this light and
detection by the human eye.
Sunlight
• Sunlight is one source of white light. The
colors appear in sunlight due to the fact that
many different elements are excited inside
and at the surface of the sun. The emission
lines from these spectra combine to form
the continuous white light spectra we are
familiar with.
• Not all of the frequencies are represented
equally in sunlight, although all are present.
• Most prominent are frequencies in the
yellow/green region.
• Read the relevant sections of your texts
regarding:
– Thin Film Interference
– Color Additions and Subtractions
– Primary Colors of Light vs. Primary
Colors of Pigments