Ks number counts in the Groth and Coppi fields

We have used William Herschel Telescope/INGRID K-s images on two high-latitude fields, the Coppi and Groth strips, to obtain galaxy number counts over similar to 180 arcmin(2), to a depth of K-s similar to 21.0. Detection efficiency corrections as a function of object size have been calculated on each pointing. We have used a signal-to-noise threshold in two complementary half-exposure images to remove spurious detections. Our data cover the range from K-s = 14.5 to K-s = 21.0, so they are useful for investigating a previously reported change in the number count slope (d log N/dm) at K similar to 17. We find a slope gamma(b) = 0.54 0.63 for K < 17.5 and a slope γ(f) = 0.25 0.29 for K > 17.5. A total contribution from galaxies to the extragalactic background light (EBL) in the K band of nuI(nu) = 10.5 nW m(-2) sr(-1) has been calculated. This K-band EBL coming from galaxies accounts for only similar to 50% of the recent measurements of the diffuse EBL. Standard number count models fail to reproduce the observed slope change at K similar to 17.5 unless elliptical and spiral formation is pushed to z less than or similar to 2.