The Olimpo balloon project will use a 120 bolometer camera to observe the sky
at $4$ frequencies ($143$, $217$, $385$ and $600\\;GHz$) with a
resolution of $3$ to $2$ arc-minute.
This paper presents the sub-millimeter calibration \"lamp\" developed
for ground testing and in-flight secondary calibration of bolometric detectors.
By design, main features of the device are reproductibility and stability
of light flux and millisecond rise time. The radiative device will be placed
inside the bolometer camera and will illuminate
the bolometer array through a hole in the last $2\\;K$ mirror.
Operation, readout, and monitoring of the device is ensured by warm electronics.
Light output flux and duration is programmable, triggered and monitored
from a simple computer $RS232$ interface. It was tested to be reliable
in ballooning temperature conditions: from $-80^\\circ C$ to $50^\\circ C$.
Design and test\'s results are explained.
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