Primary and secondary light

1. Primary and secondary light By: Brantley and Joseph

2. Primary light • A primary light source is an object that produces the light that it emits. • Primary sources can have high temperature like the sun, flames, the filament of an incandescent lamp, etc. • They can also be at room temperature using electrical or chemical processes to produce light like TV, computer, or mobile screens.

3. Secondary light • These objects don't produce the light they emit, instead they have received light from a primary source first or even a secondary source. • They diffuse light in all directions. • So a secondary source can only be considered as a source of light when it is lighted by that of a primary source or secondary source.

4. Secondary light • The Moon ( that receives its light from the Sun ) and planets are considered secondary sources that diffuse (spread throughout) some light (like a movie screen lighted by a projector.) • However, if you’re in a room with a shining lamp, every object in the room including you is considered a secondary light source

5. PIgment colors • Chemicals that are capable of absorbing one or more frequency of white light are known as pigments. • Materials that have been spreaded throughout by specific pigments will selectively absorb specific frequencies of light in order to produce their own appearance. (This is why you will find more colors of pigments than you would of light.) https://youtube.com/watch?v=yu44JRTIxSQ

6. Color subtraction • The colored appearance of most objects is due to selective absorption (subtraction) in which the material absorbs some wavelengths very strongly and either transmits or reflects whatever is left. • The color is therefore produced by subtraction – A subtractive color model explains the mixing of a limited set of dyes, inks, paint pigments or natural colorants (substance that colors something) to create a wider range of colors, each are the result of partially or completely subtracting (absorbing) some wavelengths of light and not others.

7. Color subtraction • "CMY" • Before TVs and computer monitors, printers and publishers wondered if they could print color pictures using just three colors of ink. • It is possible, but you have to work in reverse of the process of mixing light colors. • We see light colors by emission from the source. • We see pigment colors by the process of reflection. • The colors which are not reflected are absorbed or subtracted. • The subtractive primary colors are cyan, magenta and yellow, also known as CMY. -These are the three colors used in printer ink cartridges.

8. Color Addition • The mixing together (or addition) of two or three of these three primary colors of light with varying degrees of brightness can produce a wide range of other colors. • For this reason, many t.v and computer monitors produce the range of colors on the monitor by the use of red, green and blue light-emitting phosphors (a synthetic fluorescent).

9. Behavior of light waves • Adding more pigments into a paint mix will dull its appearance. • Browns, greys ,and ultimately black will result. • But doing the same with light will create a paler light and eventually white. • If you stare at a colored light, its complementary color will imprint upon the retina. • This will be seen when the eyes are closed. • For example: A red light will leave a green afterimage; a yellow light will leave a violet afterimage. • It can be seen from this that light and pigments have something in common. • They have the same complementary colors.

10. Visible spectrum of light • Bright white light comprises all the colors, as can be seen if a beam of light was shone through a prism. • Red light has the longest wave length of the visible spectrum and can be perceived on an outer edge of the split light beam. • Violet light has the shortest wave length of the visible spectrum and would be visible on an opposing edge. • All the other colors we see will lie somewhere between, in the order of: violet, blue, green, yellow, orange, red and magenta. • All these colors are but a hair-thin slice of the electromagnetic radiation.

11. Pigments versus Light • When it comes to color behavior, light behaves in opposing ways to pigments. • The primary colors of light are the secondary colors of pigments. • Mixing a given color pair together will bring different results in light and pigment. • Adding more colors to the mix will dull or darken the color in paint, but will appear paler and brighter in light. • The only thing they have in common is their complementary colors. • But mixing complementary colors together will result in black in pigment; but white for light.

12. Pigments versus Light cont. • Complementary colors are two opposing colors that can be found on the color wheel. • We can see in both the ‘light wheel’ and the ‘pigment wheel,’ that the complementary color of green is magenta; the complementary color of violet is yellow, and the complementary color of blue is red. • In both examples of light and pigments, placing complementary colors side by side will create a shimmering effect, often used in art. • However, mix any two complimentary colors together, and in light, white will result; in pigment, black will result.

13. Mixing colored light cont. • Take a pot of red light and a pot of green light; two primary colors of light, and let them overlap, and yellow will shine back. • Take a pot of violet light and a pot of green light, again, two primary colors of light, and bright cyan will result. • Mix all three primary colors together, and you will not get black, as would be the case of pigments, but white. https://youtube.com/watch?v=4Iw_UNsUtEM

14. Works cited • The Physics Classroom(1996-2016, January 1). Color Addition. Retrieved from http://www.physicsclassroom.com/class/light/Lesson-2/Color-Addition • The University of Colorado(2017, January 1). Subtraction of Colors. Retrieved from http://www.colorado.edu/physics/phys1230/phys1230_fa01/topic47.html • Webscaping.co(2017, January 1).Colour Addition. Retrieved from http://www.cyberphysics.co.uk/topics/light/colorAddition.html • The Physics Classroom(1996-2016, January 1). Color and Vision. Retrieved from http://www.physicsclassroom.com/class/light/Lesson-2/Light-Absorption,-Reflection,-and-Transmission

15. Quiz (part 1) “CMY” • A primary light source produces its own light? True or False • Which one of the following is not a primary light source? A) The sun B)A Fire C) Your reflection in a mirror D) Your phone screen • Secondary light sources reflect light in which directions? • Adding more pigments into a paint mix will _____ its appearance. • Chemicals that are capable of absorbing one or more frequency of white light are known as ________. • Selective absorption is also known as color ________.

16. 7. What three colors are used in printer ink cartridges? 8. ____ light has the longest wave length of the visible spectrum and can be perceived on an outer edge of the split light beam. 9. When it comes to color behavior, light behaves in _______ ways to pigments. 10. If you are in a room with a incandescent candle in the middle of the room, and in the room there is the following: You, a chair, a trash can, a mirror, and a book. Which are considered secondary light sources, or would they all be?