Electromagnetic Spectrum

2. Electromagnetic Spectrum

3. Speed of Light • Light travels both as a wave and as a particle • It always travels in a straight line (as long as the medium remains constant) • Has the symbol ‘c’, instead of ‘v’ • c = λf • c = 3.00 x 108m/s

4. Sources of Light • A luminous object emits light waves. • Luminous flux (P) is the rate at which light is being emitted. • Lumen (lm) is the unit of flux • 100 watt light bulb = 1750 lm • All light bulbs are rated in lumens.

5. Sources of Light • An Illuminated object reflects light. • Illuminance is how much light strikes a surface. • The symbol is ‘E’ and it is measured in lux (lx) • Not the same as flux • 1 lx = 1 lm/m2

6. light bulb = flux (lumens) Illuminated surface = lux

7. Inverse square law for light r r area of the surface of a sphere = 4 π r2

8. Inverse square law for light ¼ 1/9 1/16 0 m 1 m 2 m 3 m 4m E = P Illuminance = flux 4 π d2 4 π r2

9. Inverse square law for light (for candle power or candela (cd)) ¼ 1/9 1/16 0 m 1 m 2 m 3 m 4m P = 4 π cd E = cd d2

10. Photometry • The intensity of an unknown light bulb can be found by comparing it to a known light source. • A screen is placed between the two lights and moved until the illumination is equal on both sides.

11. Photometry Known 1000 lm Unknown ? lm 1.5 m 2.1 m

12. Photometry P1 = P2 d12d22 1000 lm = P2 (1.5m)2(2.1 m)2 P2 = 2004 lm Known 1000 lm Unknown ? lm 1.5 m 2.1 m

13. Photometry #2 Sometimes the intensities of the light bulbs are known and the location of the screen is not known. 650 lm 800 lm 0.75 m d2

14. Photometry #2 P1 = P2 d12d22 650 lm 800 lm (0.75 m)2 (d2)2 d2 = 0.83 m 650 lm 800 lm 0.75 m d2

15. Color

16. Colored Light Newton was the first to prove that white light is made up a spectrum of colors.

17. Primary Light Colors The primary light colors are Red, Green, and Blue

18. Secondary Light Colors The secondary light colors are Cyan, Yellow, and Magenta.

19. Color Addition Primary Secondary Red + Green = Yellow Blue + Green = Cyan Red + Blue = Magenta Red + Blue + Green = White light

20. Complimentary Colors If a Primary plus a Secondary Color are mixed, White light will be produced Blue + Yellow = White Red + Cyan = White Green + Magenta = White

21. Color Subtraction Paint or Dye absorbs a primary light color and reflects a secondary light color. If all three colors are added, the object will appear to be Black ( it absorbs all the primary light colors)

22. Color Subtraction Yellow, Cyan, and Magenta are the primary pigment colors. Yellow – absorbs blue, reflects red + green (yellow light) Cyan - absorbs red, reflects blue + green (cyan Light) Magenta – absorbs green, reflects blue + red (magenta light)

23. Color Subtraction The Blue object, absorbs the red and green light in the white light and reflects the blue light.

24. Color Subtraction What would the color of the object appear to be if only Red light was used? Green light? Blue Light?

25. Color Subtraction What would the color of the object appear to be if a Yellow light was used? Cyan light? Magenta Light?