The pressure- and light-induced emissions of four aldehydes-benzaldehyde (BA), 4-(dimethylamino)-benzaldehyde (DMABA), 4-(dibutylamino)-benzaldehyde (DBABA), and 4-(dimethylamino)-1-naphthaldehyde (DMANA)--dissolved in solid polymers have been investigated. All compounds studied exhibit under pressure as well as under continuous irradiation a significant enhancement of the luminescence emission. In the case of substituted aldehydes, both the fluorescence and phosphorescence increase markedly when pressure increases. For BA only increasing phosphorescene is observed. These changes are explained in terms of a model which takes a mixing of the lowest triplet state character as a controlling factor of the pressure effect. Thus, the pressure-induced emission arises from a decrease of the n,pi* character of the lowest triplet state and as a result an increase of its radiative rate and decrease of the intersystem crossing. The lowest triplet state is also assumed to be a precursor for the Light-induced effect. In this case, the emission is proposed to occur as a result of the tripler reactivity and consequently the creation of a light-emitting species.