# Is power still consumed when we switch off the lights?

I was having heated discussion with one of my friends. We were discussing Earth Hour and its role in saving electricity, and creating awareness.

He stated that even if you turn off the lights, the load from the transmission lines is there at you home, so power is still being consumed.

But then I replied that, Power P $= I^2R$. and since there is no current flowing in the household equipments( whose R is much higher than that of the transmission lines), so there is no(or negligible) power loss.

Please tell which logic is correct, and whether switching off the unused electric/electronic equipments helps to save power or not?

• Oh, my bad. Apology. – ABcDexter Apr 19 '16 at 19:30
• I still do not get the point of the question. Indeed switching off the electric equipment helps. Your friend is however partially right - there are some small losses (and other expenses) in the electricity distribution network on its own, and you probably pay your little share for these in some constant fee on your bill. – dominecf Apr 19 '16 at 19:33
• @dominecf The main question is related to the futility of something like Earth Hour. Does switching off lights on a massive scale help for sustainable development/saving resources or not? – ABcDexter Apr 19 '16 at 19:39
• (comment moved to an answer) – dominecf Apr 19 '16 at 19:51
• Yes, exactly. Also, please write this as an answer :-) – ABcDexter Apr 19 '16 at 19:53

First answer this: does it take more power to run one light bulb or two?

Transmission lines are designed to be low loss, but they run a long way. Lightbulbs are designed to be "lossy" because that's how they work. Let's say for the sake of argument that the whole transmission circuit loses 100 watts and you're talking about a 100 watt bulb: those numbers are likely not anywhere close to accurate, but that's conceptually irrelevant. With the light on, the circuit uses 200 watts; with the light off, it only uses 100 watts. Then if we assume that the realistic scenario is that transmission losses are close to negligible, the extrapolation is that removing the household load saves a lot of energy.

As devil's advocate though, I'd like to point out that lights really don't account for much energy usage in the average home. Major appliances such as the refrigerator, air conditioners and electric ranges or water heaters pull much higher wattages, and tend to run often during the day, while lights are only useful in interior rooms or at night. So perhaps the better option for "Earth Hour" is to improve our overall energy efficiency to reduce usage.

I believe the main effect of Earth Hour is in attracting public attention to sustainability. But besides of it, without doubt it saves energy (... and natural resources as well as one's wallet) if one turns off their unused light.

The scale of one hour savings on turning off dispensable lighting for one hour is however rather small compared to other means how our civilisation wastes energy.

• Will the power plant supplying my city burn less fuel if I put off the lamps? If not, then we aren't saving any energy and I don't know where it will go. – Tofi Apr 19 '16 at 20:38
• Yes, I believe at least a soup spoon of coal will be saved if one turns off a 50 W bulb for an hour. – dominecf Apr 19 '16 at 20:42
• @VIP If the power grid operators are smart, they can store the extra energy in various ways. For example, hydroelectric generators are reversed and used to pump water back uphill to store excess output of other power plants whose output cannot be varied quickly. So yes, if the grid is well run, it will overall burn less fuel. The main potential effect is economic: ultimately if people use significantly less power, the power generators are simply not going make something they can't sell. – WetSavannaAnimal Jun 23 '16 at 10:55