Download Light`s Interaction with Objects in the Universe

PRE-LAB

Luminous bodies emit light (i.e. – stars)

Luminous Flux (P) is the rate at which visible light is
emitted from a source
 Units: Lumen (lm)
 A typical 100 W light bulb emits ~1750 lm
PRE-LAB

Illuminated bodies are actually reflecting light
from another source (i.e. – the Moon)

Illuminance (E) is the rate at which light falls on a
surface
 Units: Lumens per square meter (lm/m2) = Lux (lx)
 Area used is that of a sphere 4πr2

Luminous Intensity (I) is the luminous flux that
falls on 1 m2 area 1 meter from a source

Units: Candela (cd) – “candle power”
PRE-LAB

Albedo is the reflecting power of a surface.



It is the ratio of reflected radiation from the surface to incident
radiation upon it.
Albedo depends on the frequency of the radiation.
Since it’s a ratio, albedo is expressed as a percentage
decimal:



0 = no reflection of a perfectly black surface
1 = perfect reflection of a white surface
The average overall albedo of Earth, its planetary albedo, is 30 to
35% because of cloud cover, but widely varies locally across the
surface because of different geological and environmental
features.
POST-LAB


The further away a luminous or illuminated body is, it
appears to be less bright
This pattern follows an inverse square law:
𝐼1 𝑑2 2
= 2
𝐼2 𝑑1