What does high background mean?
A high background implies that impurities, such as cell debris and salts, are binding to the probe array in a nonspecific manner and that these substances are fluorescing at 570 nm (the scanning wavelength). This nonspecific binding causes a low signal to noise ratio (SNR), meaning that genes for transcripts present at very low levels in the sample may incorrectly be called Absent. High background creates an overall loss of sensitivity in the experiment.