Hi,
The LAMP 5G R16 brochure states the dimensions with mount are 276 x 267 x 133 mm. I'm assuming most of this (big) size is due to the mount rather than the device.
What are the dimensions of the unit itself (without the mount)?
I quickly measured the picture, parametrating to the known measures.
I would say that the body is square so (viewed from top) 133x133 (but there is the cable gland protruding from the back, that will be around 40-50 mm).
Height seems to be 190-210 mm.