We present a detailed analysis of the behaviour of the Red Clump K -band absolute magnitude ( M _ { K } ^ { RC } ) in simple and composite stellar populations , in light of its use as standard candle for distance determinations .
The advantage of using M _ { K } ^ { RC } , following recent empirical calibrations of its value for the solar neighbourhood , arises from its very low sensitivity to the extinction by interstellar dust .
We show that , as in the case of the V - and I -band results , M _ { K } ^ { RC } is a complicated function of the stellar metallicity Z and age t .
In general , M _ { K } ^ { RC } is more sensitive to t and Z than M _ { I } ^ { RC } , for high t and low Z .
Morever , for ages above \sim 1.5 Gyr , M _ { K } ^ { RC } decreases with increasing Z , the opposite behaviour with respect to M _ { V } ^ { RC } and M _ { I } ^ { RC } .

We provide data and equations which allow the determination of the K -band population correction \Delta M _ { K } ^ { RC } ( difference between the Red Clump brightness in the solar neighbourhood and in the population under scrutiny ) for any generic stellar population .
These data complement the results presented in Girardi & Salaris ( 2001 ) for the V - and I -band .
We show how data from galactic open clusters consistently support our predicted \Delta M _ { V } ^ { RC } , \Delta M _ { I } ^ { RC } and \Delta M _ { K } ^ { RC } values .

Multiband VIK population corrections for various galaxy systems are provided .
They can be used in conjunction with the method devised by Alves et al .
( 2002 ) , in order to derive simultaneously reddening and distance from the use of VIK observations of Red Clump stars .
We have positively tested this technique on the Galactic globular cluster 47 Tuc , for which both an empirical parallax-based main sequence fitting distance and reddening estimates exist .
We have also studied the case of using only V and I photometry , recovering consistent results for both reddening and distance .
Application of this method to an OGLE-II field , and the results by Alves et al .
( 2002 ) , confirm a LMC distance modulus of about 18.50 , in agreement with the HST extragalactic distance scale zero-point .