Fig. 8.

LED stimuli were comparably strong over the projected illumination areas. (A) Each wand was held in a plastic bar with a hole drilled through it and pointed downward, 2–3 cm above the test surface to photograph the emission spots. The spots were saturated in the digital image so a perpendicular plastic surface was placed behind the projected spots to simultaneously view the reflected images of each spot, but at a greatly reduced luminance. (B) To examine relative stimulus strength and confirm that no LED was exceptionally strong or weak compared to the others, each was pointed directly at the 2 mm diameter fiber optic face of a transducer coupled to the output of a general IR phototransistor (Jellies and Kueh, 2012). Each spot was then moved away from the transducer by a fixed amount. All wavelengths produced saturating responses out to 12 cm. At 14 cm, the responses to red and green wavelengths began to fall off, then at 18 cm the responses to UV, blue and white light began to fall off.