Incandescent Lamps react in a Linear fashion to changes in the applied Voltage.
In fact, their reactions to Voltage Fluctuations is very noticable to the Human Eye.
Case in point: The way an Incandescent Lamp will "Dim and Flicker" when a Refrigerator's Compressor Motor gets connected across the Line (Motor starting).
Their "Linear" light output vs. applied Voltage works in both directions; when the applied Voltage increases, this results in a corresponding Increased Wattage draw - and an increased light output.
If the applied Voltage decreases, the Wattage drawn also decreases, and results in a decreased light output - hence the term "Linear".
If the applied Voltage suddenly drops by like 5 to 6 Volts, the Lamp Filament draws less Current - and consequently, a lower True Power (Wattage) is drawn from the Power System.
This reduces the output light intensity, and ends up with a dimmer lamp that has more orange than white light output.
If the applied Voltage suddenly increases 5 to 6 Volts, the Lamp Filament draws more Current - and consequently, a higher True Power (Wattage) is drawn from the Power System.
This increases the output light intensity and ends up with a much more intense white light output.
While driving an Incandescent Lamp with a lower than rated Voltage reduces its efficiency - and resultant output light is more orange than white, the Lamp will likely never fail ("Burn Out"). It depends on how much lower the applied Voltage is per the Lamp's rated Voltage.
There's also an energy savings, since the Lamp is now drawing less True Power (Wattage) than rated.
On the flip side, driving the Lamp with a Higher Voltage inproves its efficiency and light output characteristics (efficacy) - BUT - the Lamp's life is dramatically reduced.
Also, the energy consumed is greater than its rating, so you pay more $$$ for drawing more kWhs / making the kWh Meter spin faster.
As far as Fluorescent Lamps, they react very transiently when the applied Voltage suddenly drops or increases. Normally the rapid "Flicker" goes un noticed, but when there is a very heavy and long time Current draw on the system (like an Air Conditioner with high head pressure on the pump is started), the Lamp can be noticably flickering and slightly dimming.
Flicker and slight light output increases may sometimes be noticed during prolonged Voltage Surges. T12 Hot Cathode Operation Rapid Start Lamps driven at 60 Hz are more noticable than T8 Cold Cathode Operation Instant Start Lamps driven at >10kHz.
Most of the "Voltage Fluctuation Problem" is taken care of by the Ballast.
Linear Reactor / Autotransformer type Ballasts simply are looking at the input for an Apparent Power value (Volt-Amps). So if the Voltage drops by a few Volts, the Ballast tends to draw increased Amperage, so that the input Volt-Amps figure remains somewhat steady.
If the applied Voltage is within a certain tolerance (5% +/- Ballast's rating), there will be almost no noticable light decrease or increase.
Most of the normally used "Electronic" Ballasts (Non-Reactor/Autotransformer and High Hz type Ballasts) compensate for the applied voltage - either by a range line input rating (like 100 to 277 volts), or via the first two input circuit components (Voltage Regulation circuitry).
In either case (Magnetic or Non-Magnetic Ballast), the Ballast's main function is to limit the level of Current which flows through the Lamp(s) it is connected to.
Input Voltage correction is an "Inherited Effect"
To sum this up...
Incandescent Lamps are very noticable when Voltage fluctuates.
Fluorescent (and nearly all discharge lighting) is less noticable during "slight" Voltage fluctuations.
Scott35
