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An architectural and engineering feat in the Great Nef desert, desighned and built by Goldeneyes Silverhand Dactylos.

While not described in the text, it would appear from context that these are otherwise conventional dams, strategically located in the Nef desert to trap and channel the sluggish Discworld light, so that it can be exported and/or sold on to other parts of the Disc that need it more than a desert does. The further details of the technology/technomancy involved have so far not been disclosed to us. The Light Dams and their devisor make an appearance in The Colour of Magic.