A problem about blackbody radiation

[VHAHAHA]

The Stefan–Boltzmann law :
J = kT^4 where k is Stefan–Boltzmann constant.

but for non black body ( or grey body)
the equ becomes
J = εkT^4
where 0<ε<1

can anyone explain y a grey body emit less radiation when compare to the black body at same T? It can found the ans in wiki or the reference book "modern physics"

thank you

 

[Simon Bridge]

What is the condition it has to meet to be considered a blackbody? (Why is a blackbody "black"?)

Compare with grey.

 

[VHAHAHA]

Black body absorb all incident em wave while grey body absorbs a part of it and reflects the remains

 

[Simon Bridge]

Black-body also radiates at the same rate as it absorbs.
A grey body is just the same as a black-body but it absorbs less energy - therefore it has less energy to radiate.