Cost of electricity for light dimmer

Hardly ever true - more like 1-2% of the line voltage times load current becomes heat.

Usually the heatsinks are for dissipation of heat amounting to only 1-2% of full load power!

Please consider that a 40 watt soldering iron, maybe as little as a 15 watt one, can get the heatsinks much hotter than any normal operation would!

A 100 watt bulb dimmed to half output consumes about 74 watts. With losses in the usual dimmers, this amounts to about 75 watts.

Most likely:

1. The dimmers were not addequately conservatively designed
2. Dimmers were placed close to each other or in the same box as each other so that they added heat to each other.

However, lower wattage bulbs dimmed less do indeed give the same light for less power consumption and less dimmer heating than you get with higher wattage bulbs dimmed more.

- Don Klipstein ( snipped-for-privacy@misty.com)

This in particular is why you shouldn't use dimmers with lamps that are mounted so that the filament is above the socket. When such lamps burn out it is not uncommon for a broken piece of filament to fall and briefly short across the two thick wires that feed the ends of the filament.

Sylvia.

| You're wrong both-sorry but that's it.A dimmer is *not* a potentiometer, so | there's no energy consumed on it.Usually it has a triac (which is a simple | power electronic device, like two thyristors in anti-parallel connection).

There is SOME energy consumed there. They do get hot (some get very hot). Certainly less than a potentiometer (unless something has gone wrong), but the consumptions not zero.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

| The illumination output of a standard light bulb varies approximately by the | square of the applied power. Cut the power in half and you get about one | fourth the lumens. That is only approximate and varies somewhat with the | type of filament.

Assuming a constant filament. If you get a lower wattage filament, then you save power, lower cost, and have proportionally less light. But one factor to consider is the human sensitivity and perception of light. And that's non-linear.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

| And, as an additional issue, it's generally a bad idea to use a dimmer | with quartz-halogen lamps. When dimmed, the bulbs run a good deal | cooler, the halogen-sequestering-and-redeposition of the tungsten | doesn't work as well, the tungsten tends to plate out on the inside of | the tube and dim the bulb, and the bulb lifetime is greatly decreased.

And this is a frequent problem with those torchiere floor lamps which usually have a dimmer and a 300 (more than you need most of the time) watt QH bulb. So people dim them, usually. Unfortunately, getting a lower wattage bulb is more expensive, if they can even be found in the same size.

| All in all, as others have said, it makes more economic sense to use | smaller bulbs at full power rather than dimming a high-wattage bulb.

Agreed. Getting variability should be done in the form of turning more or fewer bulbs on. A lamp with 8 small 40 watt QH bulbs and a switch to control how many are on would be nice ... and expensive.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

| This in particular is why you shouldn't use dimmers with lamps that are | mounted so that the filament is above the socket. When such lamps burn | out it is not uncommon for a broken piece of filament to fall and | briefly short across the two thick wires that feed the ends of the filament.

I had one bulb do that in a non-brief way, once. The filament shorted in such a way that it had about 75% if it's length still working. It got brighter (in theory, from 60 watts to 80 watts if that estimate of filament length was correct. The nice thing was the light now looked a lot more "white". Unfortunately it gave out about a week later.

Someone once suggested getting 100 volt (because that is their nominal voltage) light bulbs intended for the Japanese domestic market. That would get a brighter whiter light. Just be sure to get a lot of them as you will be changing bulbs more frequently. A 60 watt 100 volt bulb run on 120 volts will be dissipating about 86 watts (NOT figuring in the change of resistance due to the change of heat). Which could be used in place of a 100 watt bulb. Power usage goes up. Light output goes up even more. Bulb replacement goes up, too.

Other people prefer bulbs rated for 130 volts so they don't have to change them so often. In hard to reach places that's definitely a plus.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

| A few bulbs benefit from "soft starting", many and probably most do not. | Most (but not all) bulbs have zero or negligible fatigue damage to the | filament from a "cold start" despite a cold start jolting the filament to | cause a "ping" sound that is audible at close range.

I've found that this can be a benefit for the small candelabra style bulbs often used in small home chandeliers. Their filaments are constructed in a different way with typically 4 vertical segments. I've had these blow very often with full starting, and noticeably less often starting dimmed. Regular bulbs haven't noticed a change.

| There is a usual prelude-to-failure uneven evaporation of the filament. | That process causes a "thin spot" that is subject to a temperature | overshoot during a cold start. In most lightbulbs, such a "deadly thin | spot" is a deterioration mode of the filament that accelerates at a rate | worse than exponentially (during operation) once it becomes significant. | This means that for most lightbulbs, when they become unable to survive a | cold start their operating hours are numbered. And for most (but not all) | lightbulbs, cold starts do zero to usually-negligible damage until the | filament has aged enough for a cold start to be fatal.

[...]

| True, but they usually don't blow out immediately unless the overload is | very severe. Mild to moderate overload merely shortens their life.

I have seen at times some strange bulb behaviour. And this without any dimmer involved. The bulbs sometimes start to hum. Or maybe they will modulate the light output around 10 Hz. In these cases I have learned they are "dead already". If others are around I'll just say "that bulb just burned out" to which they reply "but it's still giving out light". Then my reply is "when have you ever seen a light bulb just stop giving out light while its on" (it happens, but it's rare enough most people don't remember ever seeing it). I insist that it is already dead and add that it won't come back on when the light is turned off then back on. Often times someone is willing to actually try the switch and every time I've been proved right. Then they start wondering about me.

| Current surge from burnout is often worse than the current surge of a | cold start. Often when the filament breaks, an arc forms across the gap. | The arc can be encouraged by the voltage gradient across the filament to | expand and go across the ends of the filament, in which case the filament | is no longer limiting current through the arc. This is what causes the | "bright blue flash" that sometimes occurs during a burnout, especially a | burnout during a cold start (when the filament resistance is less and | allows more current to flow through the arc which makes the arc hotter and | more conductive). | Most lightbulbs have fusible links in one of their internal lead-in | wires so that a "burnout arc" does not pop a breaker or blow a fuse. | However, this may be inadequate for protection of dimmers.

I've had a few cases where the surge that resulted for a burn out arc has caused other bulbs in the same fixture to burn out. In one case, all

5 bulbs in a fixture blew at the same time. In that case, all 5 bulbs also showed multiple filament breakage, and arc damage in the base, such as melting through the base. In another case, the bulb became welded to the base. In another case, there was damage in the wiring itself. Two case tripped breakers (multiple bulb burnouts in these, too).

| I believe probably true. It gets more uncertain when you have a 600 | watt or 540 watt load on a 600 watt dimmer, and it gets worse when you put | more than one dimmer in the same box since each one adds heat to the | others (despite the loss in each dimmer being only a few watts).

Just put a 7 watt light bulb in a small metal case and leave it one for a while. Without good thermal dissipation, heat rise can be significant. Many a fire has happened from decorative items with even small bulbs used inside (such a Christmas light items).

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

| Say for instance you had four 25 watt bulbs and you needed only 25 watts | of light. Well, you switch on only one. and you get 25 watts of light | and pay for 25 watts of power. But if you dim your 100W lamp to get 25 | watts of light, then you might be paying for 50 watts of power. You get | less light per watt when it is dimmed.

The 100 watt bulb in this condition has a lower color temperature. This results in far more infrared output relative to light output compared to normal operation. It's that "orange look".

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

so

simple

connection).

Relatively small. I would expect it would be something like a normal NP junction where the voltage drop is about 0.6 volts. Assume a 50 watt load using about a half ampere current. = about 0.3 watts. Other components in the circuit may have more disappation than that.

| Relatively small. I would expect it would be something like a normal NP | junction where the voltage drop is about 0.6 volts. Assume a 50 watt load | using about a half ampere current. = about 0.3 watts. Other components in | the circuit may have more disappation than that.

Put a small wattage light in the same kind of enclosure. Experiment until you find the wattage that gives the same temperature rise over a long settling time. Then you'll have an estimate of the waste by the device.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

| I use flourescent substitutes in some places, but they're not exactly a | perfect solution either. The ones I use take a significant time | (minutes, I think) to reach their peak brightness, an effect that seems | to get worse as they age. However I've yet to have to replace one. | | I don't know that you can use a dimmer with them, though. I rather | suspect they wouldn't like that.

There are dimmable ballasts. That obviously combines the role of limiting the current and adjusting the current. I bet they are all solid-state.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/   http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

Here is a nice collection of articles about dimming fluoros:

--
Roger J.

[snip]

than

distribution.

than

higher

infrared)

I wanted to ask about this. Does that mean that a 220VAC lamp is less efficient than a 120VAC lamp, because the filament has to be much thinner, and so must be operated at lower temperature?

than

much

consider

level

on

PUSH

not.

I know that I find that the dimmers that have to be turned are *much* more inconvenient, because instead of just poking it with your hand as you go by, you have to stop and twist it. When you're just passing thru a room, it's wasteful of time and patience. And it wears the pot out faster, because the whole carbon element gets wiped by the wiper each time it's turned full on. So it will fail sooner, and my guess is the cost of replacement is much more than the savings of light bulbs you get from using this instead of push-on type.

There are also dimmers that use a touch plate, and they have a memory that turns them on at the same setting every time, without any fiddling. But these are more expensive than the usual cheap dimmer.

And there is the dimmer that's just like a switch, it has the toggle that can be moved thru its range with the same effect as a regular switch. Just push up on it quick and it's full on. This would solve the problem of twisting a regular 'volume control' pot.

[lots of good info snipped - thanks, Don.]

I believe there are two diode drops in a triac, resulting in a 1.2 volt drop.

- Don Klipstein ( snipped-for-privacy@misty.com)

In , Sylvia Else wrote in part:

A few are, such as the dimmable version of the Philips 23 watt SLS - available at Home Depot.

- Don Klipstein ( snipped-for-privacy@misty.com)

potentiometer,

hot).

but

load

in

Isn't only one diode conducting at a time? Regardless, the power dissipation is small and would be at maximum disappation when the lamps are at full brightness. But it would need a heat sink. Suppose there were 8

100 watt bulbs. Say 10 amperes. The power disappated by the Truac could be 12 or 6 watts.

There was some correspondence in New Scientists about the impact of mains overvoltages on the life of incandescent lamps. Something along the lines of a 10% overvoltage halves the life.

It's just possible that the lamp manufacturers really have chosen an operating point that represents the best choice for the majority of people.

I use flourescent substitutes in some places, but they're not exactly a perfect solution either. The ones I use take a significant time (minutes, I think) to reach their peak brightness, an effect that seems to get worse as they age. However I've yet to have to replace one.

I don't know that you can use a dimmer with them, though. I rather suspect they wouldn't like that.

Sylvia.

This is indeed true. And 12V ones are more efficient than 120V ones.

There is another reason that applies with gas-filled bulbs: Making the filament thicker makes the "boundary layer" of gas around the filament thicker, and reduces the temperature gradient in this "boundary layer" of gas. That reduces the amount of heat conduction loss by the gas per unit area of the filament. In fact, if the filament has much less than somewhere around 10 watts per centimeter of visibly-apparent length, they usually put a vacuum in the bulb instead of the usual argon-nitrogen mixture. With really thin filaments, the heat conduction disadvantage of the gas outweighs its advantage of enabling higher filament temperature by slowing filament evaporation.

Now for what happens with really low design voltages: With a high temperature gradient along the ends of the filament, heat conduction through the ends of the filament becomes a more significant loss.

For wattages around 20-100 watts, if design voltage is variable, to maximize efficiency with a given life expectancy in mind the optimum design voltage is not far from 12 volts. For just a few watts it's closer to 6 volts. For around a watt or a fraction of a watt it's closer to 5 volts.

Here's an example: The 1156 automotive backup light bulb typically produces 400 lumens from 26.9 watts at 12.8 volts with a life expectancy of 1200 hours. That's 14.9 lumens/watt. A 120V 40 watt lamp designed to last 1000 hours gets about 12.6 lumens/watt.

- Don Klipstein ( snipped-for-privacy@misty.com)

I have a 3 kW heat sink cooled by a fan.

No - wait, I think that's my room heater.

Sylvia.