Solid-state hid lamp dimmer

A lighting control apparatus which is responsive to a variable and controllable demand signal to control the power input to a high-pressure-discharge lamp means and thus vary the light output therefrom while preventing the lamp means from extinguishing because of a too-rapid reduction in power input thereto, said lamp means under normal full-power operating conditions displaying a predetermined voltage drop thereacross, said apparatus comprising:

• a. ballasting means connectable in series with said lamp means and an AC power source, said ballasting means comprising a reactance means variable between a minimum value which causes said lamp means to operate at a maximum light output and a maximum value which causes said lamp means to operate at a minimum light output;
• b. solid-state switching means connected to said ballasting means to controllably vary the reactance of said ballasting means in response to a timed control signal to vary in a controlled fashion the power input to said lamp means and thus vary the light output therefrom;
• c. signal generating means responsive to said demand signal to generate a control signal timed to occur at a variable and controllable point in each half cycle of said AC power source, the output of said signal generating means connected to the input of said solid-state switching means, and said generated timed control signal rendering said solid-state switching means conductive for a variable and controllable portion of each half cycle of said AC power source;
• d. lamp voltage sensing means for developing a feedback signal which varies in accordance with the voltage drop across said lamp means;
• and
• e. signal sensing and overriding means for sensing the magnitude of said feedback signal when said lamp means is operating with less than substantially maximum power input and with a voltage drop thereacross which is greater than the normal predetermined rated operating voltage therefor and for causing said sensed feedback signal to override said control signal and increase the power input to said operating lamp means and thus decrease the voltage drop thereacross, whereby the tendency for said lamp means to extinguish during dimming thereof is compensated for.