Light

Directional

Just like sun light, light position means nothing,

the only thing matters in directional is drection

Point

Just like candle light, it has no direction, it illuminats every direction

It has attenuation, so does spot light.

attenuation = 1 / (constant + liner * d + quadratic * d ^2 )

d is distance between object  and light position in 3d space

Spot Light

Just like flashlight

if  cosα   <= cos(φ/2), no light received

if  cosα   >= cos(θ/2), max light received

if  cos(φ/2) <  cosα < cos(θ/2) 

    Intensity = ( (cosα - cos(φ/2)) / (cos(θ/2) - cos(φ/2)) ) ^ falloff