There are some very persuasive arguments for the use of instant-start electronic ballasts; the laboratory lighting designer should consider them before deciding which electronic ballast to specify.
The instant-start ballast is more economical—5 to 10 percent less expensive—than the rapid--start ballast. This can become a significant difference given the numbers of ballasts required to operate an entire lab complex. The instant-start ballast will also provide greater energy savings of about two watts per lamp. The rapid-start ballast uses more energy because it must maintain current to the cathode to maintain cathode heat; the instant-start ballast essentially blasts the cathode into operation, so it does not require constant current to maintain lamp operation. Two watts per lamp multiplied by thousands of lamps in a laboratory can have a significant impact on energy use.
In typical settings, lamps are on for periods of time greater than three hours per start. Lamp life tends to even out between the lamps driven by rapid- and instant-start ballasts after about eight hours of continual operation, so reduced lamp life resulting from instant ballasts becomes irrelevant under these conditions.
Instant start fixtures work by causing the lamp to initially "strike" or light by applying an initial voltage to the lamp that is many times greater than the lamps normal operating voltage and greater than the lamps break-down resistance, essentially starting the lamp with brute force. The starting voltage is so great (as high as 940 volts in some models) that even if the gas is extremely resistant, it will usually conduct. Some instant start fixtures also create a potential between the fixture and lamp cathodes to generate ionization, which helps lower the starting resistance of the lamp.
Once current starts flowing through the lamps, the lamps illuminate at close to their full brightness. After a successful start, the instant-start ballast will immediately regulate the voltage and current down to the normal operating levels.
Traditional instant start lamps could be identified by having either a single pin on each end of the lamp, or by having recessed contacts. (Recessed contacts are used in "High Output" lamps containing "HO" in the lamp model number.) However, with the advent of electronic ballasts, the newer T-8 (1.0" diameter) "F0" and "FB0" series lamps are bi-pin designs but are meant for use with special instant start ballasts.
Because of the higher voltages and current involved with these fixtures, older instant-start designs using
core and coil ballast employ special lamp sockets that are designed to disconnect the fixtures power source when a lamp is removed. Most electronic ballasts do not need this interlock, as the ballast is able to detect the absence of a lamp and shut down that portion of the ballast automatically. The electronic ballast designs commonly allow less than the maximum allowed number of lamps to be attached to the ballast, and the remaining lamps will operate correctly. Older magnetic ballast designs require that the stated number of lamps be connected and in working order or some or all of the lamps may not illuminate fully or at all.
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