Figure 3.

Optical properties of the LED array system. (A) The LED is positioned along the optical axis (perpendicular to the surface of cell growth). It has a spatial distribution of output determined by the half-angle or the FWHM. In the absence of an intermediate lens, spot size is solely determined by the half-angle of emission and the distance of the cellular array from the LED output lens. In the presence of a ball lens, the output of the LED is constrained into a tighter spot at the cellular array. (B) Images of an intermediate open spacer array and a spacer array loaded with acrylic ball lenses (6.35 mm diameter). (C) Spot sizes of the LED output in the cellular specimen plane in the absence and presence of the ball lenses for different arrays (502, 470, 575, and 625 nm) (all shown in grayscale). The top spot shows the size of the stimulus without ball lenses, which approximates the size of a well (7 mm) in a 96-well tissue culture dish. The smaller spots result from use of the ball lens array. See Table 2 for spot size dimensions. The speckled appearance of the larger spots is due to the illumination of nonuniformities in the paper used to image the spot sizes. (D) The optical transmission of the cell culture 96-well bottom material, either a glass or polystyrene coverslip, was measured relative to air. Glass had slightly better transmission properties below 400 nm, but both types of coverslips provided 80% transmission above 400 nm in the visible light range.