Knowledge of the glass-substrate temperature and its control is often very important in the vacuum deposition of nickel-iron thin films. Discrepancies in vacuum-component-temperature measurements and control prompted a study on the subject. A theoretical investigation showed that a large-area low-temperature radiation source would be most desirable for glass-substrate heating. Experimentation with various heating techniques resulted in two acceptable methods. A temperature variation of less than two degrees at 250 °C was achieved over a large volume.