The device should be connected to 5V power via an USB. The new version of TESS-W has a USB connector at the end of the cable. You need an extra (not supplied) USB charger as those used to charge your smartphone. Do not use a cheap one, please refer to power consumption question. Remember to place the charger in a covered outlet protected from the elements.
You can also power the TESS-W photometer using a smartphone external battery or the USB plug of your car.
A DC power source of 5V is needed. The intensity of the current ranges from 50 to 100 mA (for different WiFi signal) when the ambient temperature is over 10ºC. For lower temperatures, T < 10ºC, the resistance is activated to increase the internal temperature of the photometer in order to prevent fog in the window and also to melt frost. In this situation the current ranges from 500 to 600mA. The the power consumption varies from 0.25W and 3W depending on the external temperature
If you wish to measure sky brightness during one night while observing on the field, you can power the TESS-W with batteries (DC 5V) and record the data with the software for PC or (better option) with the smartphone app (download from the software page).
For a permanent monitoring station you could use a simple solar power kit to provide electricity. The internet connection could be provided by a 3G router. A small travel router should be enough.
The graph shows the spectral response of TESS compared with the Sky Quality Photometer (SQM) and the astronomical Johnson filters (B, V and R). The spectra of some common lamps used in street illumination are also displayed. TESS response has been extended to the red region to fully cover the High Pressure Sodium (HPS) spectrum.