  Absolute spectrophotometric measurements of diffuse radiation at 1 \mu m to 2
\mu m are crucial to our understanding of the radiative content of the Universe
from nucleosynthesis since the epoch of reionization, the composition and
structure of the Zodiacal dust cloud in our solar system, and the diffuse
galactic light arising from starlight scattered by interstellar dust. The Low
Resolution Spectrometer (LRS) on the rocket-borne Cosmic Infrared Background
Experiment (CIBER) is a \lambda / \Delta \lambda \sim 15-30 absolute
spectrophotometer designed to make precision measurements of the absolute
near-infrared sky brightness between 0.75 \mu m < \lambda < 2.1 \mu m. This
paper presents the optical, mechanical and electronic design of the LRS, as
well as the ground testing, characterization and calibration measurements
undertaken before flight to verify its performance. The LRS is shown to work to
specifications, achieving the necessary optical and sensitivity performance. We
describe our understanding and control of sources of systematic error for
absolute photometry of the near-infrared extragalactic background light.
