ECN Forum
Posted By: RobbieD Starting Of Fixtures - 04/10/07 03:32 AM
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?
Posted By: Kenbo Re: Starting Of Fixtures - 04/10/07 12:33 PM
Not read this through yet. Just quickly found this.

Should I turn off my flourescent lighting
Posted By: ghost307 Re: Starting Of Fixtures - 04/10/07 12:45 PM
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:
http://kwc.org/mythbusters/2006/12/episode_69_22000_foot_fall_lig.html
Posted By: RobbieD Re: Starting Of Fixtures - 04/10/07 09:02 PM
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.
Posted By: Trumpy Re: Starting Of Fixtures - 04/13/07 10:11 AM
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.
Posted By: RobbieD Re: Starting Of Fixtures - 04/13/07 09:48 PM
Yes, that is how the fixtures work. Was there a point ???
Posted By: Scott35 Re: Starting Of Fixtures - 04/14/07 04:01 AM
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;
and
* "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
--
Posted By: Scott35 Re: Starting Of Fixtures - 04/17/07 06:10 AM
***BUMP***

RobbieD;

Were any of these replies helpful?

Scott
Posted By: RobbieD Re: Starting Of Fixtures - 04/19/07 12:35 AM
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!
Posted By: HLCbuild Re: Starting Of Fixtures - 04/20/07 01:34 AM
Scott...it was helpful to me...thanks for the explanation.
Posted By: winnie Re: Starting Of Fixtures - 04/23/07 08:27 PM
A nugget of truth which Scott35 mentions, and which is also described in the Lighting Design Lab article:

_Starting_ a lamp can _cost_ as much as running that lamp for a significant period of time.

Starting a lamp will eat into its useful life. Lamps take energy to produce, transport, install, and dispose of. So anything that shortens the life of the lamp is using up some of that 'latent' energy.

Rather than calculating the number of kWh is used up simply to have the lamp, it generally makes more sense to talk about the monetary cost of having that lamp. The lamp itself might cost $1 or $2; but you also have to pay the labor for relamping, as well as costs for disposal, so for a quick back of the napkin calculation, it is fair to say that a lamp costs $10.

Depending upon the technology of the lamp and ballast, you will get anything from 5000 to 200000 starts per lamp (the 200000 is claimed by a manufacturer for a modern and expensive program start ballast, and I'll belive it when I see it.) Say you get 10000 starts per lamp...this says that starting the lamp costs $0.001.

Say the lamp uses 40W after you account for ballast efficiency, and electricity costs $0.10 per kWh. This tells us that it costs $0.004 per hour to run that lamp.

With these assumptions, starting a lamp _costs_ the same as running it for 15 minutes.

I had to pull a bunch of numbers out of my left ear, and costs in a particular situation may be vastly different (especially if you have the program start ballasts), but the cost of starting a lamp is _not_ negligible, even if the power usage is.

-Jon
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