  We show experimentally that the effects of "slow and fast light" that are
considered to be caused by spectral hole-burning under conditions of coherent
population oscillations (CPO) can be universally observed with incoherent light
fields on objects with the pure-intensity nonlinearity, when such an
interpretation is inapplicable. As a light source, we used an incandescent lamp
and as objects for study, a photochromic glass and a thermochromic coating. The
response of the objects to intensity modulation of the incident light
reproduced in all details the commonly accepted experimental evidences of the
"light with a negative group velocity" and "ultraslow light". We come to
conclusion that so far there are no experimental works providing evidence for
real observation of the "CPO-based slow or fast light".
