When a fluorescent tube is lit, it is emitting rays of light, from all points around its circumference.
When the tube in question is over a vivarium, any rays emitted from the top half of the tube are directed away from the vivarium, and are wasted.
By using a suitable reflector behind the tube, it is possible to obtain the maximum efficiency from the tube, because this otherwise lost light energy is re-directed to where it is required - into the vivarium.
All Arcadia reflectors are manufactured from sturdy corrosion resistant aluminium, and the design is such that they can easily be mounted to the vivarium inserting the lamp clips through slots in the reflector.
The reflector can then be angled to direct the light.