A logic circuit includes a logic unit, a driving unit, and a voltage level adjuster. In accordance with the present invention, the temperature forming the lower switch-on threshold of the heater and the temperature forming the upper switch-off threshold of the heater vary. In an example embodiment, the light apparatus is a lamp. The masking agent can have a grain size comprised between 10 and 100 m, with a Gaussian distribution. The desktop is restricted in the common environments to a predetermined set of resolutions as defined by VGA and SVGA standards.