title: Pulse-modulated light source for psychometric and vision experiments.
abstract: Light-emitting diodes (LED) of various colours were used to produce accurately controllable light sources. Variable light intensity was obtained by applying 800-ns current pulses to the LEDs at frequencies 1-1000 kHz using a single potentiometer. These current pulses were generated from an oscillator which was voltage-controlled from a potentiometer and an antilogarithmic amplifier. Its output was gated to produce an optional flicker of 1-100 Hz. The light intensity was indicated by a frequency meter connected to the oscillator. The reading of this was found to linearly indicate light intensity.
mesh_terms: D003119:Color Perception Tests / Q000295:instrumentation; D003623:Dark Adaptation; D005425:Flicker Fusion; D006801:Humans; D010775:Photic Stimulation / Q000295:instrumentation*; D011594:Psychometrics; D012684:Sensory Thresholds; D014787:Vision Tests / Q000295:instrumentation*; D014785:Vision, Ocular / Q000502:physiology