  Among highly irradiated exoplanets, some have been found to undergo
significant hydrodynamic expansion traced by atmospheric escape. To better
understand these processes in the context of planetary evolution, we propose
NIGHT (the Near-Infrared Gatherer of Helium Transits). NIGHT is a
high-resolution spectrograph dedicated to surveying and temporally monitoring
He I triplet absorption at 1083nm in stellar and planetary atmospheres. In this
paper, we outline our scientific objectives, requirements, and cost-efficient
design. Our simulations, based on previous detections and modelling using the
current exoplanet population, determine our requirements and survey targets.
With a spectral resolution of 70,000 on a 2-meter telescope, NIGHT can
accurately resolve the helium triplet and detect 1% peak absorption in 118
known exoplanets in a single transit. Additionally, it can search for
three-sigma temporal variations of 0.4% in 66 exoplanets in-between two
transits. These are conservative estimates considering the ongoing detections
of transiting planets amenable to atmospheric characterisation. We find that
instrumental stability at 40m/s, less stringent than for radial velocity
monitoring, is sufficient for transmission spectroscopy in He I. As such, NIGHT
can utilize mostly off-the-shelf components, ensuring cost-efficiency. A
fibre-fed system allows for flexibility as a visitor instrument on a variety of
telescopes, making it ideal for follow-up observations after JWST or
ground-based detections. Over a few years of surveying, NIGHT could offer
detailed insights into the mechanisms shaping the hot Neptune desert and
close-in planet population by significantly expanding the statistical sample of
planets with known evaporating atmospheres. First light is expected in 2024.
