The Unihedron "Sky Quality Meter" is a small calibrated light meter that can accurately measure sky brightness. Please refer to the Light Pollution page to see the definition of sky brightness measures. The Unihedron measures in units of "magnitudes per arc-second squared". This can be related to the "Bortle" scale of sky brightness, and is also a measure of artificial-to-natural brightness. The brightness is on a log scale, so tremendous differences in brightness make ony a small difference in the Unihedron measurement. Most of the "dark" nights in El Dorado Hills (on the edge of the light dome of Sacramento, but usually facing to the East, toward "Sierra Skies" (hence the name of our observatory), is in the range of 19.5-20.0 mag/arc-sec^2.

This version of the Unihedron is called the SQM-L, which has a lens that limits the FWHM (field-of-view) of the meter to about 20 degrees, in contrst to the SQM (without lens), which has a FOV of about 40 degrees. Also available is the SQM-LE, which is ethernet-connected, so that the sky brightness can be readout remotely (which is what we should now have, mounted on the observatory).