Download Will Reducing The Line Voltage Save Energy?

Frequently Asked Questions
Miscellaneous Topics
Will reducing the line voltage save energy?
Filament Light Sources:
Incandescent and Halogen Lamps – Reduced line voltage will save energy. How much? The answer is related
roughly to the square of the reduced line voltage. For example, a 10% reduction yields 90% (0.90) of the
original line voltage and 90%2 = 81%. Therefore, the energy savings is approximately 19% (100% - 81%) for
a 10% line reduction.
Discharge Light Sources:
Fluorescent Lamps – Some electronic ballasts with passive front ends will save some energy if the line voltage is
reduced. While this relationship between energy savings and light voltage is not exactly a 1-to-1 ratio, it is
close. A 5% line voltage reduction will produce about a 5% reduction in the system input power. However,
electronic ballasts with active front ends (like older Motorola or the newer SYLVANIA Universal Voltage)
have regulating power supplies, which means they compensate for lower line voltage by drawing more
current, thereby keeping the input power constant. With these ballasts, there is no power reduction and no
energy savings.
HID Lamps – Energy savings for HID lamps also depends on the ballast.
•
For HID lamps using a standard high reactance magnetic ballasts (usually labeled HX), the line voltage
regulation of the ballast is poor, meaning you actually get more power reduction than line voltage reduction.
For example, a 5% line voltage reduction causes a 10% reduction in lamp power. Applying this 5% line
voltage reduction at the system level, a system that was drawing 450W will now draw about 410W (assuming
an HID lamp at 400W X 0.9 = 360W; add back the ballast losses of 50W, and the result is 410W for the
system). This 40W savings represents 10% of the lamp power or 9% of the system power.
•
For HID lamps using a Constant Wattage Autotransformer (CWA) ballast, the relationship between line
voltage and power reduction is about 1-to-1. A 5% line voltage reduction will produce a 5% reduction in the
lamp power. At the system level (using the same example as above), the power would be reduced 20W
(from 450W to 430W).
•
For HID lamps using a Constant Wattage (CW) ballast, also known as a "three winding" or "three coil"
ballast, the line voltage regulation is very good. A 5% line voltage reduction will produce about a 2½%
reduction in lamp power. Again using the same 5% line voltage reduction, the power would be reduced 10W
(from 450W to 440W).
Motor Loads: For most types of HVAC motors, pump motors, refrigerators, etc., there is little or no savings since
induction motors, by nature, regulate themselves by drawing more current when the line voltage drops. A 10%
FAQ0067-0605
OSRAM SYLVANIA
Visit our website: www.sylvania.com
1-800-LIGHTBULB
© 2005 OSRAM SYLVANIA
line voltage reduction would not cause any reduction in input power to the motor, and therefore, no energy
savings. To save energy with motors, devices called Variable Frequency Drives (VFD), which adjust input power
based on actual motor loads, are usually used.
Electronic Devices: Personal computers, printers, copy machines, etc. also have regulating power supplies, so there
is little if any energy savings with a line voltage reduction.
FAQ0067-0605
Visit our website: www.sylvania.com
1-800-LIGHTBULB
-2-
© 2005 OSRAM SYLVANIA