Naked Science Forum
Non Life Sciences => Technology => Topic started by: neilep on 14/09/2008 18:04:20
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Dear Light-Bulbologists,
As a sheepy I am of course the proprietor of a number of light emitting devices !....well, it goes without saying really doesn't it ?
Woolly Four Legged Ruminant Mammals of the Genus Ovis = Owner of lights !...bloody obvious really !...blatant in fact !!
So, whilst dosing some shopping recently in Tesco* (US Peeps- TESCO* is a ' store ' , A ' store ' is a place where ewe buy things from !...I think ewe may have some too...check your town center !)...anyway, TESCO* (the 'store') had a special deal going on some GE energy light bulbs for 68p each !!..Now, where I come from (a hill in Wales) that's a bargain !...so I bought a load and set upon myself the task to exchange the bulbs in my house !
Here is an example of a bulb in a lamp (I have labeled the two to assist ewe)
[ Invalid Attachment ]
But *le sigh* I'm distraught !...It says on the pack that I can NOT put the bulbs in sockets where dimmer switches are used !!...
I'm so peeved off I wrote to my neighbour to complain !..he hasn't responded yet but I did notice a 'FOR SALE' board going up this morning just a few hours after banging on his door, ringing his bell, shouting through his letterbox and finally posting my complaint through his letterbox at 3am this morning...followed by the contents of my cats litter tray (which contains the contents of their little bot-bots !)
So, why can I NOT put an energy saving light bulb in a socket attched to a dimmer switch ?
I wish I knew !!..I don't though !!!.. I want to know..If I did know then I'd be rather a silly sheepy for asking ewe this then wouldn't I ?......and as ewe all know I am the height of sensibility !
Hugs and shmishes
neil
Enegery Bulb Enquirer
xxxxxxxxxxxxxxxxxxxxxxxxxxxx
mwah mwah mwah
* Energy light saving bulbs are also available at other equally good stores but if TESCO want to send me a £100 voucher and a years supply of money then that would be just simply super of them !
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GE Energy bulbs. There's the answer. Genetically Enhanced Energy bulbs need a good kick up the fundamentals to get going. Dim and Dimmer switches are wusses and just don't cut the mustard with anything genetically enhanced and their superior attitude.
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GE Energy bulbs. There's the answer. Genetically Enhanced Energy bulbs need a good kick up the fundamentals to get going. Dim and Dimmer switches are wusses and just don't cut the mustard with anything genetically enhanced and their superior attitude.
So, regular switcheys have the ooompth needed to power a less powerful bulb !!
...whereas a wimpy dimmy switchy has no chutzpah to regulate the power required eh !!
Well this is what I also thought, ...the good thing is I never saw any anti-genetically enhanced protestors donning placards in the store, nor have I witnessed them destroying crop fields of where the genetically enhanced bulbs are grown !
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Another possibility, of course, is simply that I posted a total load of old blx [:D]
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Reducing the voltage supplied, using a dimmer, drops the voltage below the threshold necessary for the arc in the fluorescent bulb, and the arc is extinguished, not dimmed. Regular (incandescent) bulbs do not have this property of requiring a threshold voltage to glow, so their light output can be continuously varied by changing the voltage.
http://en.wikipedia.org/wiki/Fluorescent_lamp#Dimming
Dimmable domestic fluorescent bulbs are available, but cost more than 68p...
http://www.acehardwareoutlet.com/(fj2j5gi25zk0fv55coagdc55)/ProductDetails.aspx?SKU=3237120 (NB: USA 120 Volts, UK 240 Volts)
They incorporate their own dimming circuitry, i.e. do not require (incandescent) dimming "switches".
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Dimmer switches do not reduce the voltage supplied.
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Precisely; they alter the period, per mains cycle, for which the mains is supplied to the bulb / device ( on all the time for max brightness and half the time for 'half' brightness). Unfortunately, most dimmers assume that the load is a simple resistance and 'wait' to turn on at the appropriate time to let the right amount of current (hence, the charge) through that resistance.
Discharge type bulbs are not simple resistors and the average dimmer is too dim to cope. Also, the components of the bulb 'expect' to get a sinusoidal supply and they don't, so the whole system fails.
Amazingly, I have never tried the experiment as I would not be surprised to find that I had bust the dimmer. Could I try it in your house please?
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THANK EWE ALL for your wonderful responses !
I consider myself educated and it's all thanks to ewe lot !
Please pat yourselves on the back and enjoy the moment this happiness has brought ewe !
Sophie...Of course ewe can try it at my house *goes to find JimBobs address* [;D]
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How many posters does it take to change a light bulb?
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Go on then.
Or was it just a rhetorical question?
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There is a long answer somewhere on the Internet.
Starts something like.... out of 1000 posters.. 234 argue it should be 'lamp' and not bulb.
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Well, a 'lamp' is the whole thing. The glass bulb is the thing which you replace - unless your 'er indoors and you are changing the decor.
That shows you how much posters know about things. But 76% got it right - better than New Theories would suggest.
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HOW MANY GROUP POSTERS DOES IT TAKE TO CHANGE A LIGHT BULB?
1 to change the light bulb and to post that the light bulb has been changed
14 to share similar experiences of changing light bulbs and how the light bulb could have been changed differently
7 to caution about the dangers of changing light bulbs
27 to point out spelling/grammar errors in posts about changing light bulbs
53 to flame the spell checkers
41 to correct spelling/grammar flames
6 to argue over whether it's "lightbulb" or "light bulb" ...
another 6 to condemn those 6 as anal-retentive
2 industry professionals to inform the group that the proper term is "lamp"
15 know-it-alls who claim *they* were in the industry, and that "light bulb" is perfectly correct
156 to email the participant's ISPs complaining that they are in violation of their "acceptable use policy"
109 to post that this group is not about light bulbs and to please take this discussion to a lightbulb group
203 to demand that cross posting to hardware forum, off-topic forum, and lightbulb group about changing light bulbs be stopped
111 to defend the posting to this group saying that we all use light bulbs and therefore the posts *are* relevant to this group
306 to debate which method of changing light bulbs is superior, where to buy the best light bulbs, what brand of light bulbs work best for this technique and what brands are faulty
27 to post URL's where one can see examples of different light bulbs
14 to post that the URL's were posted incorrectly and then post the corrected URL's
3 to post about links they found from the URL's that are relevant to this group which makes light bulbs relevant to this group
33 to link all posts to date, quote them in their entirety including all headers and signatures, and add "Me too"
12 to post to the group that they will no longer post because they cannot handle the light bulb controversy
19 to quote the "Me too's" to say "Me three"
4 to suggest that posters request the light bulb FAQ
44 to ask what is a "FAQ"
4 to say "didn't we go through this already a short time ago?"
143 to say "do a Google search on light bulbs before posting questions about light bulbs"
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Cuantos Bloggers hacen falta para cambiar una bombilla?
Humor friki clásico, visto en Emezeta:
14 lectores para compartir experiencias similares a los cambios de bombillas.
5 lectores para comentar cómo se podría haber hecho de forma diferente.
7 lectores para prevenir sobre los riesgos de cambiar bombillas.
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As an experiment I tried powering a simple power measuring device via a dimmer which rather surprisingly led to its destruction.
On inspection I found the device used a very simple power supply consisting of a half bridge fed via a capacitor and no voltage regulation, when the dimmer was turned down there was effectively an increase in supply frequency with the reduced impedance of the capacitor and an increase in the voltage output of the power supply circuit that destroyed the electronics !
Moral use dimmers with caution !
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As an experiment I tried powering a simple power measuring device via a dimmer which rather surprisingly led to its destruction.
On inspection I found the device used a very simple power supply consisting of a half bridge fed via a capacitor and no voltage regulation, when the dimmer was turned down there was effectively an increase in supply frequency with the reduced impedance of the capacitor and an increase in the voltage output of the power supply circuit that destroyed the electronics !
Moral use dimmers with caution !
I don't understand this; why did the frequency change?
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Quote from: syhprum on Yesterday at 20:28:11
the device used a very simple power supply consisting of a half bridge fed via a capacitor and no voltage regulation, when the dimmer was turned down there was effectively an increase in supply frequency with the reduced impedance of the capacitor and an increase in the voltage output of the power supply circuit that destroyed the electronics !
I don't understand this; why did the frequency change?
A pure mains-power sine wave has a frequency of 50 or 60Hz (depending on country; Japan has both).
Any distortion of a sine wave introduces higher frequencies into the waveform at multiples of the original 50Hz or 60Hz. It is normal to find some 3rd harmonic noise on the mains (ie 150 or 180Hz).
A triac dimmer stays off until a certain point in the waveform, when it turns on suddenly. This sudden change introduces frequencies well into 100kHz or higher (it is only regulations limiting Radio Frequency Interference that stops it going up to MHz).
From the description, the power meter used a very simple power supply without a transformer; instead they used a series capacitor to drop the mains voltage (typically 110 or 240V) down to a suitable voltage for the electronics (typically 5-10V AC).
The impedance of the capacitor is inversely proportional to frequency. A simple power supply like this can cope with a small amount of 3rd harmonic noise, but the capacitor becomes a virtual short-circuit when faced with large amounts of noise at the 1000th harmonic or higher. This applies excessive voltage to the electronics, frying it.
If the manufacturer had used a transformer to derive 5-10V AC from the mains, the voltage on the secondary would be a distorted sine wave. The dimmer would have decreased the voltage to the electronics, causing it to malfunction at the dimmest settings.
A decreased supply voltage is preferable to blowing up the electronics (but a transformer is more expensive, physically larger, heavier and gets hotter than a capacitor).
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A triac dimmer stays off until a certain point in the waveform, when it turns on suddenly.
I didn't know that; how do they do that?
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Look at the volateg waveforms here:
https://en.wikipedia.org/wiki/Dimmer#Solid-state_dimmer
- Semiconductor Diodes are 2-layer devices
- Bipolar Transistors are 3-layer devices
- TRIACs are 4-layer devices, and can be considered as two transistors back-to-back, connected so that they are both initially off, and stay that way until they get a pulse of electricity. Then one turns on, turning on the other one, which turns on the first one more... This positive feedback results in the device turning on extremely rapidly, and staying on until the voltage drops to zero, waiting for the next pulse.
By providing a timed pulse, synchronised to the mains waveform, you can control the amount of power delivered to an incandescent lamp.
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Look at the volateg waveforms here:
https://en.wikipedia.org/wiki/Dimmer#Solid-state_dimmer
- Semiconductor Diodes are 2-layer devices
- Bipolar Transistors are 3-layer devices
- TRIACs are 4-layer devices, and can be considered as two transistors back-to-back, connected so that they are both initially off, and stay that way until they get a pulse of electricity. Then one turns on, turning on the other one, which turns on the first one more... This positive feedback results in the device turning on extremely rapidly, and staying on until the voltage drops to zero, waiting for the next pulse.
By providing a timed pulse, synchronised to the mains waveform, you can control the amount of power delivered to an incandescent lamp.
It's quite complicated isn't it? I could really do with a walk-through diagram to show what is happening at each stage of the waveform to understand how it works.
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The diagrams below show the sine-wave AC voltage waveform of a 240VAC mains supply.
- The peak voltage rises above 240V, but on average, it will deliver the same power as 240V DC
- You have to imagine this pattern continues for 100s or millions of cycles
The next large graph shows the current that would be drawn by a 100W incandescent light bulb.
- This is a resistive load; it gets more complex if the load is inductive or capacitive
- This is effectively the same current that would be applied to the light bulb if you set your dimmer to "maximum brightness"
The smaller graphs on the right show what happens if you turn the dimmer knob farther towards the "dim" setting.
- The TRIAC acts like a very fast power switch, which is initially OFF
- After a small delay, a timer circuit turns on the TRIAC switch, turning on the light bulb
- The TRIAC switch turns off again when the AC voltage crosses 0V
- Depending on how you set the dimmer knob, the current to the light bulb may be turned on almost all the time, or hardly at all.
- This allows you to adjust the brightness of the light from almost full brightness to almost off.
- Switching the light bulb on and off 100 or 120 times a second is not usually visible, because of human persistence of vision, and the thermal inertia of the light filament.
In the Wikipedia article, the timer circuit consists of:
- a variable resistor that you can turn
- a fixed capacitor
- a fixed Zener diode
- This allows you to adjust the switch-on angle from 0 to 180 degrees
In some countries, non-critical power loads (like off-peak water heaters) may be controlled by the electricity supplier by injecting signals on the power lines (you get a fee rebate for this off-peak power).
- The signals slightly move the zero-crossing point of the AC waveform
- This can result in a cyclic variation in the TRIAC switch-on point, and variation of the lamp brightness
- This is visible as a cyclic variation in lamp brightness while the AC signaling voltages are present.
The TRIAC current contains many vertical lines, which indicate the presence of high frequencies in the current, which were not present in the original smooth sine-wave AC voltage. These high frequencies are what destroyed the cheap power meter.
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Every Fluorescent bulb contain a small amount of Mercury Hg 80, which evaporates when the enhanced start-up voltage strikes the electrodes., in a standard Fluorescent light circuit. Without the recommended start-up voltage circuit the Hg 80 can not evaporate und will cause an destructive low frequency pulse in high current in the Triac circuit of a standard dimmer, designed for incandescent light bulbs.
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It's quite complicated isn't it? I could really do with a walk-through diagram to show what is happening at each stage of the waveform to understand how it works.
If you install a (free) copy of LTspice, there's a dimmer in the examples folder which you can play with to your heart's content: http://www.linear.com/designtools/software/
This is a plot of relative power as a function of triac trigger angle:
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I wonder if an incandescent lamp cap be considered as a purely resistive load, due to the low thermal inertia of the filament and the rapid change of resistivey of Tungsten with temperature the current is in no way proportional to the voltage this would seem to give a capacitive element to the impedance.
It would be interesting to feed a lamp via an inductor from a DC source and see if an oscilation could be produced
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It's true that the resistance of the filament is a fairly non-linear function of temperature: the resistance increases as temperature increases to its operating temperature. The temperature range is pretty wide from room temperature (around 300K) to operating temperature around 3000K; the resistivity changes by a factor of 16 over this temperature range.
See: http://physics.usask.ca/~bzulkosk/Lab_Manuals/EP354/ep354_thermal-radiation-lab_Tungsten-Temp-Resistivity.pdf
But the pulses of electricity occur fairly close together in time (8-10ms, depending on country). As a teenager, I used a photocell to detect the change in light output from incandescent and fluorescent lamps due to mains frequency. But the variation in temperature and resistance of an incandescent lamp is not huge, once it reaches operating temperature.
The crucial effect in capacitance is that the current increases before the voltage increases (I leads V).
- It is the opposite for inductance: V leads I.
- Both are energy storage devices - they continue to deliver a current, even when the voltage has dropped to zero.
For an incandescent lamp, the pulse of voltage increases temperature, which decreases current a bit later (V leads I, like an inductor).
But when the pulse passes its peak, the current does not continue to increase while the voltage holds the same polarity, but starts to decrease with the voltage (unlike an inductor).
- When the voltage reaches zero, so does the current.
- This is the essential characteristic of a resistor, not an inductor or capacitor
It is true that every resistor has a tiny bit of capacitance and inductance. But we can say that the capacitance and inductance of a light bulb is pretty negligible compared to the 1kΩ resistance of a 60W/240V incandescent globe.