A new superbright LED stimulator: photodiode-feedback design for linearizing and stabilizing emitted light

A new, reliable LED photic generator is described for analog stimulus presentation in vision research. A "superbright" red-emitting diode is controlled via optical feedback using a PIN-photodiode. A Maxwellian-view stimulator developed this way has been proven capable of covering intensities of retinal illuminance of over 26,000 td with a linear dynamic range of 3.7 log units. The device also has outstanding properties in linearity (distortion less than 0.12% at 100 Hz), frequency characteristics (d.c. to 2 kHz full-modulation bandwidth), stability (0.0002% fluctuation), and noise (S/N ratio greater than 76 dB).