Spontaneous and induced ultraweak luminescence (biological chemiluminescence, low level luminescence, photon emission) emitted by living systems in the spectral range 0.2-1 μm strongly depends on the character and rate of physiological processes and the state of organism. Therefore such characteristics of this luminescence as intensity I, kinetics I=f(t), spectral distribution I=f(λ) and statistical photocount distribution p(n, Δt) reflect the state of biohomeostasis. A stress-induced transition from one level of homeostasis to another one is accompanied by changes in the above characteristics. Analysis of the luminescence response of organisms to detrimental stress factors provides evidence that: (i) any stress factor causesa considerable change, usually an increase, in the total intensity I, (ii) in a reversibly perturbed biohomeostasis induced by a weak stress the biological system under study may become very sensitive to external stimuli. This synergetic behavior is reflected in characteristics of luminescence, and (iii) in the case of a deleterious stress causing an irreversible perturbation and the death of an organisms, an enhanced emission, the so-called necrotic or degradative radiation is messured. Models relating luminescence with a stress-induced perturbations in membranes oxidative metabolism or with the Q-factor of a resonant photon storage system are proposed. Also, a cybernetic or systemic approach based on the analysis of photon count time series leads to the linear stochastic model that reveals a common luminescent behavior of different organisms with a stress-perturbed homeostasis.