A gas-discharge lamp includes a discharge vessel, two electrodes, a cap, an outer envelope, and a filling of a metal halide. A slurry solution is doped with a light absorbing dye having an absorptivity sensitive to a physical parameter such as acidity, temperature or pressure. A waste-heat member is situated in a non-contacting manner with the movable body. Sets of anchoring stakes tighten the tubular assembly, having an upper segment fixing guys for tightening the tubular assembly, suspended strings to detect any player who attempts to or does trespass the limits of the forbidden zone of the court, and a lower segment which is also lodged into the ground in a removable way.