Equal first: this is not a dimmer ...

... But "only" a twilight switch, because of this very misleading Product name a star less. A dimmer would via a variable resistor consumers (mostly lamps) continuously adjusted brighter or darker. This twilight switch is preset to a fixed light value at which it switches on and off, and you can not change, at most, by so choosing the location (light or dark) that it switches as desired, so try. I use it to switch my aquarium lighting and after some trial and error I have now found the optimal location. Note is still the switching capacity 40-300 watts, so beisplsw unsuitable. for individual energy-saving lamps or similar devices with lower power.