New light sensor for the CloudWatcher

Filter selection

A standard astrophotography dichroic UV/IR filter has been chosen to reject wavelengths outside the visible spectrum. These custom-made filters serve a dual purpose: they filter the incoming light and act as weather protection windows for the sensor.

We considered photometry filters but decided against them. Broad-spectrum LED lighting is becoming increasingly common in outdoor environments, and a photometry filter tuned for a specific spectral range would give inconsistent results across different lighting conditions. The UV/IR cut filter provides a better match to the visual sky brightness that astronomers care about.

Field of view

The new sensor has a wide field of view: 100% sensitivity directly above the sensor, dropping to approximately 20% at nearly 120° from zenith. This wide acceptance angle means the sensor captures a representative sample of the sky rather than just a narrow cone — more useful for assessing overall sky darkness at an observatory.

Calibration

The sensor ships with factory calibration. Users who need greater accuracy can perform an on-site calibration — a full calibration guide is available on the calibration page.