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Science Manual – Using Video Images for Fisheries Monitoring 15

For smaller sites, a less powerful LED lamp (Table 3.1) supplied by RF Concepts

(Table 3.4) would provide sufficient light to enable fish counting. This lamp is

waterproof but cannot be immersed. When positioning lighting, remember that a lot

of light will be absorbed at the water surface and that infrared light is rapidly

attenuated in water.

3.3.3 Floodlights

Security floodlights can be deployed in air to illuminate the area. Red filters can be

attached to reduce any potential impact on fish movements. Floodlights will not be

suitable for a stand-alone battery-powered site, due to the high power requirements.

3.3.4 Fluorescent tube lighting

Fluorescent tubes are used for overhead lighting above some resistivity weirs where

suitable covering or housing exists. This is generally restricted to the non-spate rivers

like the Test and Itchen, but is effective in providing good quality images for analysis

and motion detection.

An underwater light box using fluorescent tubes as its light source was fitted to the

bottom of a fish pass on the Cardiff Bay Barrage. The subsequent poor reliability,

high maintenance and overall cost of this deployment, together with the recent

technological advances of LED lighting, means that this method is not a viable

option.

Figure 3.5: A covered resistively weir lit by fluorescent tubes, River Test

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