Rheostats and comparitive usage while on holidays

[redsquash]

1 Going on holidays
Will the amount of electricity for 10 lights turned on be the same if , if,a Rheostat is used at half the brightness with 20 lights turned on over 2months?


2
If not how would the two compare?


3
Does a Rheostat consume the same amount of electricity for a set of lights but only allow a certain amount to be used with the rest being lost in heat generated?

 

[Scott No Mates]

If you are going away, why leave lights on? Anyone watching the house will know your lack of comings and goings.

A rheostat will generate heat and use about as much power as not having one. The rheostat will state how much power it uses to dissipate the energy used by the lights. Change globes to lower wattage compact fluoros.

Buy a couple of cheap timers if you must have light for the rodents and motgs but they aren't scared of the dark.

 

[redsquash]

If you are going away, why leave lights on? Anyone watching the house will know your lack of comings and goings.

A rheostat will generate heat and use about as much power as not having one. The rheostat will state how much power it uses to dissipate the energy used by the lights. Change globes to lower wattage compact fluoros.

Buy a couple of cheap timers if you must have light for the rodents and motgs but they aren't scared of the dark.

Hi Scott,
I am not going away on holidays but put it in so I dont have people hijacking the thread .When people reply they always seem to try to answer other questions , or say its not expensive so dont bother, or get a timer or something not really related.
Thanks fro your answer . I have LEDs and no facility for a timer btw

 

[Scott No Mates]

Is a timer in the fuse box on the lighting circuit an option?

 

[vaughan]

Install 5 watt LED bulbs. Very efficient.

If by "rheostat" you mean a dimmer: most of the modern fluro and LED bulbs cannot work with dimmers. If you have dimmers, check your bulbs are compatible (and the dimmers are the right type -- leading or trailing edge -- not all can be compatible).

 

[Morbius]

1 Going on holidays
Will the amount of electricity for 10 lights turned on be the same if , if,a Rheostat is used at half the brightness with 20 lights turned on over 2months?

2
If not how would the two compare?

3
Does a Rheostat consume the same amount of electricity for a set of lights but only allow a certain amount to be used with the rest being lost in heat generated?

I guess the answer depends on whether the device you are putting in the circuit is actually a rheostat or not.

A rheostat is a variable resistor and as such will dissipate heat. If you have a resistive load like an incandescent bulb and you vary the rheostat such that half the energy is being given off by the bulb, then the current has been reduced to (1/sqrt(2))*(original current). This means that the total resistance is now sqrt(2) times the original total resistance - i.e. the rheostat resistance is (sqrt(2) -1) times the resistance of the bulb. Dissipation in the rheostat is hence (1/sqrt(2))*(sqrt(2)-1)*(original energy dissipated) = .29 times. In other words, if you have a 100W bulb and then insert a rheostat and turn it so the bulb is dissipating 50W, the rheostat will a be dissipating another 29 watts.

I am not certain if, under these conditions, the incandescent bulb will be half as bright. You are reducing the current by reducing the voltage across the filament so it might well not be giving out much light at all. (i.e. all heat) You might find that at all brightness the bulb is dissipating 75W, for example. At this setting, the rheostat will probably only be dissipating 10W or so.

But since you have LEDs, I doubt very much whether a rheostat will give you the result you desire - LEDs just aren't dimmed that way. If you have dimmable LEDS, then the LED driver will have some kind of pulse-width dimmer in it and that will be much more efficient and dissipate hardly any heat at all.

 

[HomePage]

And before you go to the additional expense of dimmable LEDs and a suitable dimmer controller, the miniscule amount of power LEDs draw at full power means it would take years, if not decades, before a dimmable LED solution would pay back its acquisition costs in power savings during holiday use only.

The simplest solutions are to either not have the lights on, have only some of the lights on, or have them all on and not worry about the 1.2kw (10 lights x 5 watts x 24 hours) daily consumption.

 

[Morbius]

And before you go to the additional expense of dimmable LEDs and a suitable dimmer controller, the miniscule amount of power LEDs draw at full power means it would take years, if not decades, before a dimmable LED solution would pay back its acquisition costs in power savings during holiday use only.

Yeah. I have some dimmable LEDs because I like to be able to dim the lights, not because I want to save on electricity. In fact I have a houseful of LEDs and could pretty-much get by with a 1A breaker on the lights. In my experience a 4W-rated LED bulb seems to use less than 80% of the power of a 5W-rated CFL.

 

[HiEquity]

Yeah. I have some dimmable LEDs because I like to be able to dim the lights, not because I want to save on electricity. In fact I have a houseful of LEDs and could pretty-much get by with a 1A breaker on the lights. In my experience a 4W-rated LED bulb seems to use less than 80% of the power of a 5W-rated CFL.

A 4W anything uses the same amount of power as 80% of a 5W anything else, by definition. The question is which produces more light for the same power consumption?

In this respect, CFLs and LEDs are much the same. It's just the point source of an LED versus the distributed source of a CFL that confuses people. Along with warmup time etc. A good quality CFL or LED and driver will likely outperform a poor quality version of the other technology.

 

[Morbius]

A 4W anything uses the same amount of power as 80% of a 5W anything else, by definition. The question is which produces more light for the same power consumption?

In this respect, CFLs and LEDs are much the same. It's just the point source of an LED versus the distributed source of a CFL that confuses people. Along with warmup time etc. A good quality CFL or LED and driver will likely outperform a poor quality version of the other technology.

Not in my experience. Either because the 5W-rated CFLs were using more than 5W, or because the 4W-rated LEDs I am using are using less than 4W. I find the 4W LED bulbs I have just slightly brighter than the 5W CFLs I replaced.

This may be simply because the CFLs were old and had degraded somewhat. I have not done the comparison with two new bulbs. People have also complained in the past that LED brightness drops off with age.

 

[wylie]

Is a timer in the fuse box on the lighting circuit an option?

I'm not sure what any of these posts really mean, but if you are looking for something to make your house look lived in whilst you are away, then the timer in the fuse box is a good option. We've had that before. Turn on the kitchen, bathroom and other lights that are normally on at night, flick one switch on the fusebox timer, and they come on at night at times that you choose.

Anybody watching the house is not going to be fooled, but a dark house at 8pm is a "look at me, nobody is home" invitation, so this is a good option (especially if you cannot use portable timers).