[gego]

Back in the 1960's or 1970's there was a researcher who did experiments on the effect of different indoor lighting on plants and animals.

Florescent lights can be made with different gasses or combinations of gasses. Each gas vibrates at a characteristic frequency, which is why some of the bulbs look red, some blue and some white.

The researcher reached the conclusion that, unless the light from florescent bulbs was full spectrum, i.e., it duplicated the frequencies received in sunlight, that the florescent bulbs had a deleterious effect on life. These were serious health effects.

The saving of a little energy at the expense of your health may well be an unwise move. I do not believe that the majority of the bulbs that are available are full specturm. Additionally, since different gasses burn out at different rates, you cannot put different gasses in the same bulb without eventually having only a partial spectrum bulb toward the end of the bulb's life. True full spectrum florescent bulbs would need to be in two separate tubes so that when the short lived gas burns out you can change that tube.

I personally do not use florescent bulbs for the simple reason that I think they are dangerous.

[Zentric]

I've been researching the compact fluorescents bulbs that are coated with the special phosphors for full color spectrum lighting.

Advantages, compared with standard fluorescents, are:

* Distribution of light is centered on a more daylight-type wavelength - hence looking directly at the bulb, it appears blue (mid-day sky) instead of the standard yellow (morning sky). A technical way of saying this is that the bulb has a high color temperature (e.g., 5000 degrees Kelvin instead of the more standard 2800 degrees Kelvin).

* Full color spectrum also implies a high-percentage CRI -or Color Rendering Index - meaning that even though the continuum of colors is not flat (where, for example, there'd be equal intensities of blue, red and yellow light), it is much closer to being flat than with standard fluorescent bulbs - thus subtly-colored artwork on your wall will look good under this fluorescent light, much the same as it would look in broad daylight.

* If it is the winter and you're jonesing for sunlight, full color spectrum lighting supposedly makes you feel bright inside. The evidence of this is anecdotal from what I can tell.

Disadvantages:

* Significantly more expensive.

* Hard to locate, other than at lighting stores or by special order.

* Reduced luminosity per watt, versus standard fluorescents.

[FoxV]

btw, I haven't seen it mentioned yet but CFL's are also last around 5 - 10 times as long as incandecents (and I would bet around 20X as those $.60/pack of 4 crap)

And their actual usuable life is about double that as they don't burn out in a flash like incandescents. Their rated life span is suppose to be their half-life (burns at half brightness by X hours)

as for price and avaliablilty, we have them everywhere up hear (Big BoxMart sells them $7cnd for 3 which is a typical price)

[WisJim]

One of the reasons for bad side affects from flourescent lights is the pulsation of the light at the frequency of the AC power driving them. In the USA, this is 60 cycles per second, and this has a bad effect on people. Incandescent lights don't pulsate noticably because the hot filament doesn't cool enough to affect the lighting in 1/60 of a second. New flourescent ballasts that are electronic can have a faster rate of oscilllation and then the pulsation is at a higher frequency and has less effect on people.

I don't like the tube-type (older style) flourescents, but I use a lot of the smaller spiral style compact flourescents, and don't have problems with them. Of course, who knows what the long term side effects may be. We haven't been using electricity for long enough to know all of its problems.

[bruin]

So we have a big light in our kitchen. It has 4 60 watt bulbs in it.

However, it is on a dimmer switch.

So the question is, if you dim the lights, do you save electricity? (In other words, does the light switch itself burn the energy instead?)


I suppose the dimmer works by adding resistance to the light circuit in order to reduce the amount of current flowing into the light bulb. So lets say we have a 120V source on a 60 Watt Bulb (V*I = power) so we would have 0.5 amps of current. To get a 120V drop, our resistance would be 240 ohms.

Turn on the dimmer to 240 ohms.

We now have a 480 ohm path (lightbulb + dimmer). Our current drops to 0.25 amp (480ohms * 0.25 amps = 120V). Our light bulb is now seeing 0.25 amps of current for a 60 volt drop (.25amps * 240 ohms). Our dimmer is seeing 0.25 amps of current for a 60 vold drop too.

However, our power is now , V*I, 120V * 0.25amps = 30 Watts!

So, if this is correct, dimmers do save power!

[meekoil]

bruin,

This is how dimmer switches worked in the past.

They weren't very efficent, in your example below, the dimmer switch
would eat 15 watts that would need to be thrown off as heat.

Explaining how modern dimmers work is involved, so I looked up a link instead:

http://home.howstuffworks.com/dimmer-switch.htm

[GreyZone]

May I suggest that you replace the 4 each 60 watt incandescent bulbs with 4 each 15 watt compact flourescent bulbs? You will get the same light for 1/4th the energy cost. Or heck, install 4 each 20 watt compact flourescent bulbs (equivalent to 100 watt incandescents) and you will get far more light at 1/3rd the total energy cost.

[hanrahan]

The last time any of us saw a resistive light dimmer would probably have been decades ago at the movies. They called it a rheostat. Even that would have reduced actual current, ergo power used.

A few less years ago than that they reduced motor speed with variable inductors. We have all met these on our fans.

Assuming the dimmer you are using is one that fits behind your light switch it uses a third technology which "clips" the alternating current in a way that does not need to "burn off" excess power. More efficient again.

As an aside, the greatest advance Jobs and his mates made with the first Apple was with the power supply. Till then, to get a regulated 5V supply for the processor they designed a 7V supply and "washed off" the extra 2V with a series regulator transistor. That heat (2v*5A=10W) could not be dissapated within the small plastic case everyone loved. They devised the Switch Mode Power Supply which can regulate the 5V rail without dissapating heat. Not only that but it did not require a "large/expensive" mains transformer.

Bill

[Devil]

Switching power supplies are a LOT older than Apple. I was using a switching power supply to a DC motor in professional tape recorders in the mid-1960s. It's mark/space ratio was determined by the frequency error from a tachymetric sensor, compared to a quartz crystal divider. This meant that the tape speed was constant no matter what the instantaneous load or even movements of the recorder case (quasi-zero wow and flutter). I also designed one to control cooling fans on a 5 kW amplifier (used for vibration testing), so that the multiple output transistors were kept at a constant and uniform temperature.

Modern light dimmers simply cut in the part of each half-cycle of AC that is required. It means that, at half-power, the light bulb receives electricity for the second half of each half-cycle, the first half of each half-cycle being switched off (first approximation as the average is not RMS). There is therefore almost no power dissipated in the dimmer itself. Does not work with most fluorescent tubes, though.

[ChumpusRex]

Very little energy is used in the dimmer itself. It does waste a finite amount as heat, which is why you must be careful not to overload it.

However, the efficiency of filament lightbulbs depends very strongly on filament temperature - the hotter the filament, the better.

Halogen bulbs are more efficient (you get more light for the same electricity) because the filament burns at a higher temperature (A halogen bulb gets its name because it contains a special gas mix, including a mixture of halogens, that stops the filament evaporating at this higher temperature).

So yes, a dimmer will save energy - however, if you dim the lights to 50% brightness, you'll probably still be using 60-65% of the energy.

[oil4u]

May I suggest that you replace the 4 each 60 watt incandescent bulbs with 4 each 15 watt compact flourescent bulbs? You will get the same light for 1/4th the energy cost. Or heck, install 4 each 20 watt compact flourescent bulbs (equivalent to 100 watt incandescents) and you will get far more light at 1/3rd the total energy cost.

A great idea!! BUT compact flourescent bulbs do not work well with dimmers. Is it possible to buy CF bulbs tat are compatible with dimmers?

[Devil]

Halogen bulbs are more efficient (you get more light for the same electricity) because the filament burns at a higher temperature (A halogen bulb gets its name because it contains a special gas mix, including a mixture of halogens, that stops the filament evaporating at this higher temperature).

It is not advisable to run halogen bulbs with a dimmer. They'll work OK, but their life will be severely reduced. Why? They consist of a tungsten filament in a quartz envelope with a halogen gas inside. The tungsten evaporates as in every bulb but the atoms react with the halogen to form a tungsten halide. The heat from the filament heats the quartz so that any halide reaching it sublimes instantaneously back into a vapour form. At the filament temperature, the halide decomposes again into metal and halogen: the metal is deposited back on the filament at the hottest spot, building up its weakest point, while the halogen remains gaseous. For this cycle to occur, it requires to run at full operating temperature, otherwise the quartz will not sublime deposited tungsten halide and the filament will not be hot enough to decompose the halide. Result: shorter life.

[dbarberic]

May I suggest that you replace the 4 each 60 watt incandescent bulbs with 4 each 15 watt compact flourescent bulbs? You will get the same light for 1/4th the energy cost. Or heck, install 4 each 20 watt compact flourescent bulbs (equivalent to 100 watt incandescents) and you will get far more light at 1/3rd the total energy cost.

A great idea!! BUT compact flourescent bulbs do not work well with dimmers. Is it possible to buy CF bulbs tat are compatible with dimmers?

I have a large number of dimmer switches in my house and they DO NOT work with CF bulbs. My understanding is the dimmer switches work by cycling the lights on and off very fast. When you dim, you are actually slowing down cycling, thus lowering the light. This is why with some light bulbs, dimmer switches will make a humming or buzzing noise. That is the vibration of the filiment as it cycles on and off. CF bulbs need constant electricity to work and will not work being cycled on and off to dim them.

[ChumpusRex]

It is not advisable to run halogen bulbs with a dimmer.

You should also use a special halogen dimmer, or you need to choose a significantly more powerful dimmer (e.g. 200 W of halogen lighting will need a 500 W rated dimmer).

The amount of electricity used by a lightbulb depends on the filament temperature (the hotter the filament, the less electricity is taken). Because halogens are designed to run hotter than normal bulbs, when cold they take considerably more power than a normal bulb would - putting extra stress on the dimmer.

[Caoimhan]

There are dimmable CF bulbs, but they have to be specifically designed for it. I believe the secret is in the ballast technology used.

See HERE.

[bobbyald]

Would you say George bush has a built in dimmer switch and if so is it on full dim?

[SolarDave]

Halogen bulbs are more efficient (you get more light for the same electricity) because the filament burns at a higher temperature (A halogen bulb gets its name because it contains a special gas mix, including a mixture of halogens, that stops the filament evaporating at this higher temperature).

It is not advisable to run halogen bulbs with a dimmer. They'll work OK, but their life will be severely reduced. Why? They consist of a tungsten filament in a quartz envelope with a halogen gas inside. The tungsten evaporates as in every bulb but the atoms react with the halogen to form a tungsten halide. The heat from the filament heats the quartz so that any halide reaching it sublimes instantaneously back into a vapour form. At the filament temperature, the halide decomposes again into metal and halogen: the metal is deposited back on the filament at the hottest spot, building up its weakest point, while the halogen remains gaseous. For this cycle to occur, it requires to run at full operating temperature, otherwise the quartz will not sublime deposited tungsten halide and the filament will not be hot enough to decompose the halide. Result: shorter life.

[QUOTE]

At some point the bulb becomes dim enough (the filament becomes cool enough) that the rate of tungsten"boil off" probably becomes insignificant. I don't claim to know what that level of "dim" is, but I would expect there is a "U" shaped lifetime curve for halogen bulbs on dimmers. The "left" peak - where the bulb is so dim that the filament is barely glowing - may be higher (longer life) than the right peak, where the bulb is at full brightness. But as Devil says, somewhere in the middle is the likely to be the shortest life.

That said, it can't be too dramatically bad, as many lamps are sold with both halogen bulbs AND dimmers. We have 4 in our house of various designs.

Here is the power use of one of them measured with a "Watt's Up?":

ADAP (As Dim As Possible): 6 watts
CL (Candle Light): 11 watts
F (Feeble): 20 watts
IC (Incandescent Clone - Yellow Light): 35 watts
SHW (Still Halogen White): 65 watts
LBL (Little Bit Less than full): 90 watts
FB (Full Brightness): 104 watts

[SolarDave]

Would you say George bush has a built in dimmer switch and if so is it on full dim?

ADAP

[WisJim]

Here is the power use of one of them measured with a "Watt's Up?":

ADAP (As Dim As Possible): 6 watts
CL (Candle Light): 11 watts
F (Feeble): 20 watts
IC (Incandescent Clone - Yellow Light): 35 watts
SHW (Still Halogen White): 65 watts
LBL (Little Bit Less than full): 90 watts
FB (Full Brightness): 104 watts

Dave, have you measured the power use of the bulb in a fixture without a dimmer? I'm curious if the dimmer uses any power at full brightness. I'd check myself, but we don't have any lights with dimmers in our place.

[SolarDave]

Dave, have you measured the power use of the bulb in a fixture without a dimmer? I'm curious if the dimmer uses any power at full brightness. I'd check myself, but we don't have any lights with dimmers in our place.

All the fixtures I could test have the dimmers "built-in" except one - and the bulb is burned out in that one!

Modern dimmers probably run the power through a triac and then control the duty cycle on the AC waveform to control power. In such an arrangement, whatever the amps are for the bulb multiplied by the voltage drop across the triac is the minimum amount of power "wasted" at full brightness. For my "100 watt" lamp above, that's a watt or two.

Dimmers get warm. That's the power they use turned into heat. It's not a lot, but it is defnitely something. So yes, running a bulb at full brightness through a dimmer is slightly less efficient than not using the dimmer. "Dimming" to 97-98% or so may be a break-even. Dimming below that actually reduces energy use.