This is a very important magnitude to determine the threshold of detectability in near-infrared wavelengths. Sky brightness can be determine as follows,

SKYB = ZP - 2.5log(SK/scale2)

where ZP is the Zero Point, SK are the counts/sec/pixel from the sky and scale is the angular scale at the detector. The sky brightness is measured in magnitudes per arcsec2.
 
 

Band	Sky Brightness
J	15.40
H	13.35
K	11.90

These values were obtained on 25 August 2001.