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Peter A. Smith, John Taboada; A white-LED based dual-channel Maxwellian view stimulator for vision research. Journal of Vision 2004;4(8):311. doi: 10.1167/4.8.311.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The arrival of extremely high intensity white light-emitting diodes (LEDs) on the market presents the opportunity to modernize an old research instrument with new technology. The instrument in this case is the Maxwellian view light stimulator, which has been used extensively in vision research. Methods: We have developed a two-channel Maxwellian view light stimulator to support psychophysical studies of light adaptation using a “pulse-probe” technique, similar to the chromatic probe-sine wave observations previously described by other workers (Swanson et al, J.O.S.A., 4, 1992, Hood et al, Vision Research, 37, 1177–1191, 1997). The light stimulator utilizes state-of-the-art extremely high intensity white light emitting diodes as light sources and incorporates two channels of visual stimulation: one channel is used to provide an adaptation (pulse) field, the other the superimposed stimulus (probe) field. Both channels are presented in Maxwellian view along the same optical axis, and have variable field sizes from around 0.5 to 10°. The stimulator includes a photo-feedback control to monitor diode performance and linearity. Results: The stimulator provides for a retinal illumination over six log-trolands from each channel. Rapid and precise control of the retinal illumination over a dynamic range of around five log units could be achieved by a combination of pulse density modulation, and adjusting the LED drive current. Measurements have shown that the LED spectral output is extremely stable throughout this range. Conclusions: The utilization of high intensity white LEDs in a Maxwellian view light stimulator presents the opportunity to study retinal light adaptation up to very high levels of retinal illumination, in a highly controlled, yet versatile, instrument.
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