120V vs. 240V - is it Cheaper to Run One or the Other?
"If I run my lights at 240 Volts instead of 120 Volts, will I use less electricity?" Here at Black Dog LED headquarters in Boulder, Colorado, we are asked this question quite often, and the simple answer is yes, but only by a little. All electrically powered devices consume watts, and wattage is what you are paying for. Volts and amps are not an important factor related to electrical expenditures in an existing wired garden, although when building a new area or adding additional power to an existing area there is a possible savings in material costs and labor. To understand why there is no large electrical savings, a brief review of these electrical terms is helpful. Below we discuss Volts, Watts, and Amps, including some advantages and disadvantages of running LED lights and other indoor garden equipment at different voltages.
What are Volts, Amps, and Watts?
Voltage, wattage, and amperage; or volts (v), watts (w), and amps (a) are terms commonly used to describe and measure electricity.- Voltage or Electric Potential is the amount of electrical energy available at a source such as a plug, breaker, or extension cord—essentially how hard electricity is "pushed" through a wire. Thinking in terms of a water hose, voltage would represent the pressure of the water flowing through it.
- Amperage or Electrical Current is the amount of electricity transferred or moved through a wire or circuit. In a water hose, it would be the volume of the water flowing through it.
- Wattage or Electrical Power is how much "work" the electricity does, such as energizing the diodes in a LED grow Light. Continuing the water hose analogy, if the water exiting the hose hits a paddle wheel, the resulting rotation (work) of the wheel represents the wattage.
Watts ($) = Volts x AmpsReviewing the formula, we see that watts are determined purely by voltage and electrical amperage, so for a device requiring a particular number of watts, as voltage increases, amperage decreases. While there are some allowances made outside the scope of this article, this tip holds true for most electrical devices designed to operate at variable voltages. The only reason you can sometimes save electricity at higher voltages is that most power converters (such as AC/DC converters) get a little more efficient when run at higher voltages.
Advantages and Disadvantages
While you will not save much electricity, using higher voltage power to operate equipment in some situations makes a lot of sense. One of the main reasons people add or use 240 volt power in their garden is that there is simply not enough electrical amperage available to operate all the equipment at 120 volts. 
Power circuits are usually limited by circuit breakers in the electrical panel to prevent wires from overheating and starting fires. These circuit breakers regulate the number of amps that can flow through the circuit, regardless of the voltage.
By installing a 240V power circuit, much more electrical power is potentially available to draw from. For example if your garden had two 15 amp, 120 volt lines supplying power to the room, you would have a total of 30 amps of power available at 120 volts. Using the calculations above for the Black Dog Platinum XL-U, we can see that each light, running at 120 volts, will require 6.25 amp of available electricity. With that amperage draw, no more than 4 Platinums could be turned on before blowing a breaker. However, with just one 30amp, 240 volt line, again using the calculation above, we can see that there would be enough electricity available to run as many as nine (9) Platinum XL-U's. Since the Platinum XL-U only requires 3.12 amps when run at 240V, there would still be power available for other equipment.
Operating motors and non-digital ballasts at 240 volts does make the "start-up" process gentler, potentially increasing their lifespan. However, they are also the most common form of wasted electricity (power losses) in a garden. The power loss or lost energy is given off as unwanted heat such as that from a hot standard HID ballast. As the ballast converts or "transforms" the input power into the desired output, there is a power loss, wasting roughly 10% of the total electricity consumed. This wasted energy turns into heat, which is why ballasts are hot.