Luminous Flux• The rate at which light is emitted from a

luminous body.

• Symbol: P

• Units: Lumen Abbreviation: lm

• The total amount of light that falls on a surface.

• Symbol: E

• Unit: Lux Abbreviation: lx

Illuminance

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

24 r

PE

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.

Symbol: I

Unit: Candela, cd

2 2

4

4

PI

P IE

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 re-emits 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(single secondary color that makes white

with primary complement)

Makes white with:

Red Cyan Blue + Green

Green Magenta Red + Blue

Blue Yellow Red + Green

*Whites indicated with an asterisk (*) will represent all colors present but may be strongly hued whichever color is most present.

Color Red Green Blue Cyan Magenta YellowRed More red Yellow Magenta White Reddish

MagentaReddish 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

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