The wheel has
40 holes, each 5.1 cm diameter,
over which custom flatbottomed
quartz dishes (30 ml capacity, and approximately
18 mm deep) are placed.
Each dish is surrounded by a 2.5
cm high black collar of PVC to minimize exposure to stray
radiation among dishes. Ten specimens are placed in each
dish for exposure.
The dishes are covered with quartz lids,
and Schottt long wave pass cutoff filters (50 mm diameter,
50% transmittance at 305 6 1 nm) were placed on the lids.
Damaging UV-B radiation was provided from above the
dishes by a Spectronics XX15B UV-B lamp (with two
bulbs).
We generally cover the UV-B lamp with cellulose
acetate to eliminate the shortest wavelength UV-B and UVC
radiation that is not present in incident solar radiation
(Williamson et al. in press).
However, owing to the different
exposure times used in these reciprocity experiments, we
used Shottt glass filters here, which are more optically stable.
Lamps located in the box below the experimental organisms
provided photorepair radiation (PRR, visible, UVA,
and a small amount of UV-B from a combination of two
48 inch cool white bulbs and two 48 inch Q-Panel 340
bulbs).
The box was ventilated with a high rpm thermostatically
controlled fan.
The wheel rotated the experimental
dishes horizontally at 2 revolutions per minute to provide
uniform exposure among dishes and simulate the mixing in
the surface waters of a lake.
Black metal disks were placed
below the dishes to remove exposure to PRR. The entire
apparatus was placed inside a growth chamber with constant
temperature of 208 C.
The details of this UV lamp phototron
method approach are described in Williamson et al. (in
press).