1. The Properties of Light
Rectilinear Propagation: Light travels in straight lines.
The Pinhole Camera:

4. Diffraction: The spreading of waves as they pass through a slit.

7. Illumination, intensity and luminous flux
Intensity is the constant brightness of the light source.
Measured in candelas
40watt=35 cd 60watt= 70 cd watt =130 cd
15 watt flor = 70 cd

8. Luminous Flux Luminous flux is a measure of the power of visible light
P= 4  *I (cd)= lumens

9. Illuminance is a measure of photometric flux per unit area, or visible flux density. Illuminance is typically expressed in lux (lumens per square meter) or foot-candles (lumens per square foot).

11. The Inverse Square Law
The inverse square law defines the relationship between the irradiance from a point source and distance. It states that the intensity per unit area varies in inverse proportion to the square of the distance.
E = I / d2
In other words, if you measure 16 W/cm2 at 1 meter, you will measure 4 W/cm2 at 2 meters, and can calculate the irradiance at any other distance. An alternate form is often more convenient:
E1 d12 = E2 d22
Distance is measured to the first luminating surface - the filament of a clear bulb, or the glass envelope of a frosted bulb.

12. Example:
You measure 10.0 lm/m2 from a light bulb at 1.0 meter. What will the flux density be at half the distance?
Solution:
E1 = (d2 / d1)2 * E2
E0.5 m = (1.0 / 0.5)2 * 10.0 = 40 lm/m2

14. The Spectral Lines in the stars show the Doppler Shift due to relative motion with the earth.
v = c x (wavelength shift) / (wavelength)