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Real object radiance

Introduction

The amount of EM radiation emitted by a real object of temperature T at wavelngth \lambda is

L_%7B%5Cmathrm%7Breal%7D%7D(%5Clambda%2C%20T)%3D%5Cepsilon(%5Clambda)%20%5Ccdot%20L_%5Cmathrm%7BBB%7D(%5Clambda%2C%20T)%2C
 

where \epsilon is the emissivity and \L_\mathrm{BB}(\lambda,T) is the amount of EM radiation emitted by a black-body.

A black body has emissivity of 1, at every wavelength. It absorbs 100% of incident EM radiation; it does not reflect anything and thus appears perfectly black (assuming only reflected radiation). All absorbed radiation is emitted to maintain neutral energy balance (equlibrium).

Real objects absorb less than a black body and therefore can re-emit less (typically some 80 to 98%) of the radiation received. The emitting ability of real objects is defined by the emissivity.

Prior knowledge

Outgoing relations

Incoming relations

Learning paths