Mr Forster you are correct to the inth degree.
However, I stated at the end of my previous posts, that there are "other
factors" too !
However, I stayed with the basics.
P=E x I
Yes, I have put an accurate ohmmeter across a bulb hot and cold and yes you
are correct the resistance does change which will effect the outcome.
But, in the case I'm writing about the wattage of the glo plug would only be
higher and of course, probably, mean certain death for the glowplug
That is a fact in my, "simple math" case and your "even more" scientific
approach.
So, we did arrive at an anwer that is far greater than the 75 watts... yes!
I did state that there was an inverse law involved.
Let me state it "very" simply ...if you "halve the voltage" there are real
big approximate chance that you will "Not Halve the light" but that you
will get a quarter of the light.
Remember, this is not NASA ...but a simple little tail light bulb or a
gloplug.
Now, let's go back to a guy whose jeep taillights were very dim.
Is it a fact Mr. Foster in the real world "Basic Math" that if this
gentleman inadvertantly did put a 12volt bulb into a 6volt jeep that his
rear light would be extremely dim . Regardless of your post, saying you
can't use simple math. This little tail light will not attract one single
sumers eve' dancing moth !
Not half the voltage half as bright, but, about one quarter as bright.
Now, if that is a 6 watt tail light... just how much light would we get
using my basic math and your more thorough approach?
Just how are these guys on the MIL-VEH going to measure the hot and cold
resistance of a bulb filiament.
It takes about a second for the white hot filament to cool off beyond a red
glow to a normal cold look. Then, it further cools down to room
temperature. With the $40 meter from Radio Shack, do you think there is
enough accuracy for a Mil-Veh guy to get the readings in time?
I don't !
The damm needle would barely reach a stable reading in one second. A
digitial would hop and hunt all over the scale looking for its stable
reading. By that time it would be all over.
Mr Forster, let us take your Non basic approach to P = E x I ...then you
were a little lapse too, in your description.
What if the filament had a "Coiled Coil" manufacture ?
Would we now bring inductance into the formula ?
Of course we would
In a purist sense, especially at the instantaneous moment power is appleid.
There has to be something induced in each turn of a coil, right ?
But, Mr Forster, I gave a basic approach that "hopefully" was simple enough
to grasp what the devil might happen, if and when you double or halve the
voltage in our old vehicles from 6V to 12V and vice versa.
Mr Forster, it is a fact that if I was given a 12 volt electric wiper motor
that might wipe across the windshield and back in two second on 12 volts
...that on 6 volts it would NOT perform the same task in 4 seconds.
Now, I wont even attempt to entertain the losses in the gear train or the
pressure of the blade on the glass, either.
Of course there are many factors involved
Mostly, I feel there is the "kiss" factor that needs to be employed.
I think there are guys on our list that basic algebra might be not their
best subject. However, I'm sure though, they could put and engine and
tranny together with their eyes closed.
You are correct in you thinking Mr Forster. But this formula of Power = E
x I
Reagrds in the purist sense
Rob Pearson Upstate NY area.
A litter of jeeps
----- Original Message -----
From: "J. Forster" <jfor@quik.com>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Saturday, December 15, 2001 2:27 PM
Subject: Re: [MV] MV - Tail Lights - You Do the Math - Re Brightness
> The resistance of things like lamps and glow plugs is not constant. If you
> measure the resistance of a lamp when the filament is cold, it will be far
less
> than the resistannce of the same lamp at normal operating conditions (as
> calculated from V/I ). That's why lamps draw a high inrush current when
switched
> on. You can verify this with a small bulb and an ohmmeter. The meter
reading
> will chsange with time as the bulb filament heats up, due to the meter
current.
>
> You cannot accurately predict with simple arithmetic what the current,
power
> consumption or light output of a bulb will be when operated at other than
it's
> nominal ratings. All are power laws, of the form (V/Vnom) ^ N, where N is
some
> number. As I recall, N is 5 for the brightness of a lamp, but I'm not
certain.
>
> Also, the color temperature of a lamp varies with operating voltage, and
this
> factors into the percieved brightness. In WW II, the army used lamps
operating
> at reduced voltage, because that shifted the light output more into the
red, as
> illuminators for infra-red sniperscopes.
>
> -John
>
>
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