The assessment of light intensity preference in psychiatric patients: a questionnaire

The assessment of abnormal light-related behaviour is important for methodological reasons, and has a prophylactic and heuristic value. Since no operationalization of these behaviour patterns has been published until now, we constructed a questionnaire to identify abnormal light intensity preference based on a systematic study and previous case reports. We administered the questionnaire to patients with schizophrenia (n = 46) or major depression (n = 55), and to healthy control subjects (n = 70). Photophilia was more frequently diagnosed in schizophrenia than in depression (P < 0.001). Photophobia was more frequently observed in depression than in schizophrenia; however, this difference was not statistically significant. None of the healthy subjects showed these phenomena. The kappa value was 0.66 for photophilia and 0.65 for photophobia. Patients with schizophrenia had a higher mean photophilia score than depressive patients (P < 0.001) and healthy subjects (P < 0.05). Depressed patients had higher photophobia scores than schizophrenics (P < 0.05) and healthy subjects (P < 0.001). The photophilia score was positively correlated and the photophobia score was negatively correlated with the light intensity preference (measured by means of a photometer) (P < 0.001). A significant positive correlation between the photophilia score and the percentage of time spent in bright and very bright areas was observed (P < 0.05). Scores were not related to age or gender. These results represent initial data in support of the validity and reliability of our questionnaire for distinguishing between patients with and without abnormal light-exposure behaviour patterns.