Irregular variables of type Lb. New JHKL'M-photometry for 160 stars

This paper presents new near infrared observations of 160 Irregular variables of type Lb in the JHKL'M filter bands. These measurements are supplemented by data for additional 56 stars taken from the literature. In total 220 datasets are available because of some multiple observations. From our sample, 216 stars have near infrared (NIR) photometry now. Our sample of visually bright Lb-variables displays very similar infrared properties when compared with SRa- and SRb-variables. Derived from NIR-two colour diagrams the oxygen-rich Lbs seem to have intermediate atmospheric conditions between Miras and normal giants. There may be a sligthly larger "contamination" with non AGB-giants than in the case of the semiregulars. Using only our IR-colours the S- and the Carbon-stars among the Lbs again are undistinguishable from SR-variables of the same chemistry.