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Emergency lighting system

  • US 4,056,757 A
  • Filed: 03/02/1972
  • Issued: 11/01/1977
  • Est. Priority Date: 03/02/1972
  • Status: Expired due to Term
First Claim
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1. In combination with a lighting system comprising an alternating current utility power source, an "on-off" switch and a plurality of fluorescent lights coupled to said utility power source through said "on-off" switch, each one of said plurality of fluorescent lights being provided with a ballast, an emergency system comprising:

  • an emergency power supply having a frequency higher than the frequency of said utility power source;

    a transfer switch having a first contact directly connected to said utility power source, a second contact connected to said emergency power supply and a switch arm connected to said "on-off" switch, said transfer switch being so arranged that said switch arm is closed on said first contact when power is available from said utility power source and is automatically transferred from said first contact to said second contact when power is not available from said utility power source whereby power for illuminating said plurality of fluorescent lights is provided by said emergency power supply through said "on-off" switch when power is not available from said utility power source; and

    means for illuminating one or more but not all of said plurality of fluorescent lights when power for illuminating said plurality of fluorescent lights is provided by said emergency power supply, said ballast provided with each one of said plurality of fluorescent lights presenting such a high impedance to said higher frequency power from said emergency power supply that each one of said plurality of fluorescent lights cannot be effectively illuminated from said higher frequency emergency power supply through its respective said ballast.

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