Emergency lighting system

An electrical lighting circuit for powering a gas discharge light from a DC power source, said lighting circuit comprising:

• a DC/AC inverter for converting DC power from said source into AC power, said DC/AC inverter generating AC power at a first frequency when powering said light and at a second frequency when said light is disconnected from said lighting circuit;
• means for applying said AC power to said light;
• and
• frequency-sensitive means connected in parallel with said light, said frequency-sensitive means having a sufficiently high first impedance at said first frequency so that little power is dissipated in said frequency-sensitive means and said frequency-sensitive means having a second impedance at said second frequency so that said frequency-sensitive means provides a load to said AC power at said second frequency for preventing damage to said DC/AC inverter if said light is removed from lighting circuit.

An electrical lighting circuit in which a gas discharge light is powered by an AC power source operating at a first frequency and by a DC power source int he absence of AC power, said lighting circuit comprising:

• a ballast connected in series with said AC power source and said light, said ballast generating electrical noise;
• a DC/AC inverter for converting DC power from said DC power source into AC power at a second frequency which is substantially higher than said first frequency, said DC/AC inverter being directly connected in parallel with said light;
• and
• frequency-sensitive means connected in series with said light and said DC/AC inverter, said frequency-sensitive means having a first impedance at said first frequency so that said frequency-sensitive means tends to block said noise and said first frequency signals and to prevent said noise and said first frequency signals from being applied to said DC/AC inverter and said frequency-sensitive means having a second impedance at said second frequency so that the loss caused by said frequency-sensitive means in series with said light is reduced at said second frequency.

An electrical lighting circuit in which a first gas discharge light is powered by an AC power source and a second gas discharge light is powered by a DC power source, said lighting circuit comprising:

• means connecting said first light to said AC power source to operate said first light from said AC source;
• switch means connected in series with said AC power source and said first light to turn said first light on and off;
• a DC/AC inverter for converting DC power from said DC power source into AC power, said DC/AC inverter comprising a free-running oscillator controlled by a feedback loop;
• means for connecting said DC/AC inverter to said second light to operate said second light from said DC/AC inverter;
• means connected in said feedback loop and responsive to the presence of AC power at said first light for controlling said oscillator to operate and generate AC power to operate said second light.