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#161922 04/09/07 10:32 PM
Joined: Feb 2003
Posts: 231
RobbieD Offline OP
Everynow and again somebody at work says that starting some fluorescent fixtures takes as much power as it takes to keep it lit for an hour and sometimes they even say for longer. I tell them that is wrong. I would like an easy way of explaining to them that it doesn’t take that much power but I am finding it hard to put it into words.

Say a fluorescent fixtures draws .5A. The voltage is 120V and the pf is .85

Now that would be 51 watts.

If the fixture is on for an hour that would be .051Kw/h of power

If it takes say 1 second for the fixture to start I will have to take my above .051Kw/h and see how much power that would be in 1 second.

51watts x 60minutes = 3060w

So 3060 watts for 1 minute is egual to 51 watts for an hour.

3060watts x 60 sec = 183600w

So 183600 watts for 1 sec is the same as 51 watts for an hour.

So they are telling me that it takes 183600 watts for 1 second to start this fixture. No Way, lol.

Is this a good way of explaining (using math) that it doesn’t take that much energy to start? Or is there a better way?

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Joined: Apr 2006
Posts: 233
Not read this through yet. Just quickly found this.

Should I turn off my flourescent lighting

der Großvater
Joined: May 2005
Posts: 984
Likes: 1
As much as I think that these guys tend to be full of loose stool...the Mythbusters did a decent job of gathering data when they tested this one.
It's the 2nd entry on this page:

Joined: Feb 2003
Posts: 231
RobbieD Offline OP
Thanks, that will make it easier for the non believers to see that they are wrong. I will tell them that it was busted on MythBusters and then they will believe me. Those guys really know how to show things in a scientific and non complicated way.

I really like that show.

Last edited by RobbieD; 04/10/07 04:03 PM.
Joined: Jul 2002
Posts: 8,443
Likes: 3
A Mains voltage fluorescent fitting does not start at line voltage.
It uses the ballast to create the strike voltage, lasting nano-seconds, through a collapsing field in the ballast itself, to ionise the gas vapour in the tube and create an arc, hence the flash.
After that, the ballast controls the current to the circuit.

Joined: Feb 2003
Posts: 231
RobbieD Offline OP
Yes, that is how the fixtures work. Was there a point ???

Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and
Please excuse the extremely late reply... just wanted to toss in a few things.

First off, I have heard the same "It Cost 5¢ Each Time A Light Is Turned On" Bandini Story - regarding Incandescent Lamps and Fluorescent Lamps.

Last tally is around 1,209 times, being told that Fertilizer Story! wink

Truth is, there will be an increased - yet extremely transient - draw of True Power (Wattage). It will be so insignificant that the kWh Meter's Rotating Register (on older type Analog Meters) will not even be affected by the slight offset.

Incandescent Lamps would result in a larger transient starting draw - as they draw True Power in a Linear fashion.
The "Cold" filament of the Incandescent Lamp at start translates to a larger inrush Current - and since "I" and "E" are "100% In-Phase" (Power Factor = 1.00) throughout the Lamp's operation , there will be an increased True Power draw during startup.
Since the duration is - at most 250 ms (milli seconds), and the starting draw is - at most 5x running power, the resultant in overall work (kilowatt hours) is unmeasurable.

I would believe that the starting draw may be something noticeable (like an additional 1/4 rotation of the meter's register), if there were like 200 individual 1,000 Watt Quartz Halogen Lamps being started all at the same time - and the meter has a high rotating register speed (somewhere in the Rr=1 range).

For Fluorescent Lamps - a lot depends on the starting methods employed (rapid start / hot cathode, instant start / cold cathode, preheat / cold cathode).

Nevertheless, the True Power draw is mostly what represents the output Light (in all forms) from the Lamp(s).

With "Hot Cathode" Lamp operation, a small fraction of True Power is drawn by the Lamps' "Filaments" (AKA: the Cathodes). This Power is drawn from initial starting, throughout the entire operation.
(FYI: this is the chief reason for the push to not use Rapid Start / Hot Cathode Lamp operation in California - not that Rapid Start is "Illegal", only that it has become "phased out" in a way - the better option is "Programmed Start", which may be discussed later if wanted).

Back to the Fluorescent Lamps:

For "Preheat" Lamp operation, the Cathodes must be preheated prior to anything happening (sending an Arc down the pipe, and eventually establishing + sustaining a nice fat, hot plasma).
This method includes:
* "Manual Start" - where a button is pushed in and held for a second or two, then when released the Lamp(s) will operate;
* "Trigger Start" - where a "Starter" is used to automatically heat the Cathodes at start, then switch out for normal run.

These "Preheat" methods apply Line Voltage + Current _DIRECTLY_ from the AC Line, to the Lamps' Cathodes - in order to heat them for sufficient starting.
You can see evidence of this by observing the glowing Cathodes prior to the initiating Arc.

The level of Current is completely dependent on the _TOTAL RESISTANCE_ of the Cathodes (Filaments).
The Line Current is drawn from a Non-Ballasted source (directly from the AC Line input), and is run through the Cathodes in a Series Circuit configuration.

This type of operation results in nearly 100% True Power (close to 1.00 Power Factor) drawn by the Cathodes for starting purposes - and this True Power does not directly contribute to usable output light.
So, in reality, this would be a waste of $$$ for True Power consumption.

The level of True Power would be - at most - 4 Watts per Lamp, and the preheat time would be - at most - 2 seconds.

Rapid Start techniques are similar to the Preheat methods, only that the Rapid Start "Lag Time" is less than 100 ms.

Instant Start (Cold Cathode operation) has an upwards swinging True Power draw, which tapers off to a steady level within 500 ms of starting the Lamp(s).

Starting the Lamp(s) in this manner results in a low Power Factor start, tapering up to a High Power factor operation.


To sum things up:

* Repeatedly turning Lamps On, then Off only results in warn out switches, excessive effort put out by the "Switcher", and lower Lamp life - _NOT ANY SIGNIFICANT TRUE POWER CONSUMPTION!!!_

* Some types of Fluorescent Lamps (preheat) would be difficult to add up higher kWh costs from rapid and repeated "On/Off" switching,

* Leaving Lamps on will result in kWh consumption, as to the drawn True Power level for that type of Lamp, over a period of time,

* Someone really started one heck of an irritating "Electrical Myth" with this whole Lamp starting debate!

Personal stories:

1: My Wife's Uncle tried that Bandini Logic on me one time - happened to be a "Decora" type switch controlling an Incandescent Lamp (Decora style switches are fancy toggle switches, with a "rocker" type cover, instead of a standard handle).

The Decora switch made it really easy to "Rapid Fire" the light on and off.

I went to turn on the Lamp, and for some reason, I accidentally slipped, causing the switch to rapid fire on/off, then on.
Immediately He (Wife's Uncle) spewed out the "It Costs A Nickel Each Time You Do That" statement - which most likely was his last time, as I went directly into "Engineer Mode"!

Asked him "How would this occur?"
Response was in regards to inrush.
I take him to the kWh Meter, asked someone to rapid fire the Lamp a few times, and told him "I will pay you $10.00 if the first dial moves half way between the two numbers, while that light is rapid fired".

Long story short, I walked away with the $10.00, and one agitated Uncle-in-Law!
(he never says anything about Electrical Myths with me around anymore!!!).
In Hindsight, I should have bet him $10.00!!!

2: Some Bandini slinger on a job site had to toss out the same "Male Bovine Fecal Matter Story", in this case - relating to Fluorescent Lamps.

Went through the same procedures, but this time the "Fertilizer Distributor" stormed off frustrated and embarrassed, as everyone began wise cracking him after the "debunking" was completed!

Anyhow, long winded story, I know eek

Just a bit more ammunition for your war against stupid Electrical Legends!


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and


Were any of these replies helpful?


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Feb 2003
Posts: 231
RobbieD Offline OP
Thanks, they were helpful. I know that people are wrong when they say things like that. I was looking for an easy way to dispell this myth. I will tell them to download that episode of mythbusters.
It always amazes me how many people think that this is true, lol.
You would figure that electricians or anyone with knowledge of electrical would know right off the bat that this myth is bogus but thats not the case. Oh well thanks for the info guys!

Joined: Dec 2004
Posts: 209
Member was helpful to me...thanks for the explanation.

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