Light comes from light sources for example Sun, Star,Moon, Electric lamp, Gasoline lamp, Fire, Candle, Fire fly

Visible light

James Clerk Maxwell has shown that Visible light travels as Electromagnetic wave of a constant speed in a vacuum and in air with a visible wavelength 400-700 nm

• Speed of visible light

${\displaystyle v=C=\omega _{o}=\lambda _{o}f_{o}={\sqrt {\frac {1}{\mu _{o}\epsilon _{o}}}}=3\times 10^{6}m/s}$

• Wave length of a visible light

${\displaystyle \lambda _{o}=400-700nm}$

• Threshold frequency

According to Planck, all matter radiates visible light at Threshold frequency, fo . Hence,

${\displaystyle f_{o}={\frac {C}{\lambda _{o}}}}$

${\displaystyle f_{o}={\frac {3\times 10^{6}m/s}{400-700nm}}}$

• Energy of visible light

${\displaystyle E=pv=pC=p\lambda _{o}f_{o}=hf_{o}}$

With

${\displaystyle h=p\lambda _{o}}$

Light and matter

Visible light interacts with matter creates the following effects

• Heat transfer
• Matter's shadow .
• Colored lights