Emergency lighting system

#This invention relates generally to power supplies for lighting systems; and, more particularly, to a system that will provide emergency operation of a lighting system when power is not available from the normal power supply. Emergency power lighting systems are well known in the art. These prior art systems utilize, for emergency power, various combinations of primary batteries, secondary batteries, electric generators and/or other comon sources of power. Some systems use one source exclusively, while others use various combinations of several power sources. However, common to a majority of these systems is the fact that the form in which the emergency power is available from the source is not the form which is suitable for the end use (i.e., batteries supply low voltage D.C., fluorescent lamps prefer high voltage A.C.). For this reason nearly all emergency lighting systems employ some type of inverter (usually a solid state inverter) to convert the available power to the preferred form.

#In the prior art systems two basic approaches have been utilized. In one of these basic approaches, all components of the system, including the batteries, are located in or near the light fixture. In these systems the components are operating in a hostile environment. The most significant degrading factor being the well known sensitivity of batteries to heat.

#In addition to the heat problem, other problems are encountered with these systems. Additional wiring other than that needed to operate from the utility power is required. This additional wiring is expensive and may be inconvenient to provide. The components of the system are generally inaccessible for servicing. The inaccessibility for service contributes to reducing the life expectancy and reliability. Also, during emergency operation the lamps are not controlled by the normal "on-off" switch and if the system is not properly installed, localized failures can cause the lights to be out in one part of the building without the emergency system recognizing that a failure has occurred. This inability to recoginze a power failure can occur if the battery charging supply is not connected to the same branch circuit as the normal supply for the fixture; the branch circuit may fail, thus cutting off the lights while the emergency apparatus is still receiving power from a different branch circuit. Under these circumstances, emergency power will not be supplied to the branch that has lost normal power.

#A complete understanding of the invention can be obtained from the following detailed description when read in conjunction with the annexed drawing in which the single FIGURE shows a block diagram of an emergency lighting system embodying the principles of this invention.

#Referring to the drawing, the single Figure shows a generalized form of the lighting system constructed in accordance with this invention. In the Figure, block 3 represents the normal utility power source. As utilized for lighting, source 3 is generally a 110 volt, 60 cycle source. The dotted box 6 represents the emergency power supply. A transfer switch 4 is shown closed on utility power source 3. Transfer switch 4 also has a contact connected to emergency power supply 6. The switch arm of transfer switch 4 is connected to an "on-off" switch 5 by means of line 7.

#The lighting system shown in the FIGURE, comprises a plurality of fluorescent lamps represented by the blocks 21, 22 and 23. While only three such lights are specifically shown, anynumber of lights could be provided as indicated in the FIGURE. In addition to the fluorescent lights, the system also includes incandescent lights as represented by the blocks 61, 62 and 63. As was the case with the fluorescent lights, the system may include more than the three incandescent lamps 61, 62 and 63 specifically shown as is indicated in the FIGURE.

#Each of the fluorescent lights 21, 22 and 23 is provided with a conventional ballast as is indicated by the blocks 41, 42 and 43, respectively. The block 44 also represents a ballast which would be provided for a fourth fluorescent light not shown. Of course, any additional fluorescent light would also be provided with such a ballast.