# Can somebody please explain why..........

#### Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

•  Subject
• Author
• Posted on
......... the instructions for my Lightforce handheld spotlight states:
"Shortening cable length can be responsible for VASTLY  shortening globe
life"? How would shortening the power lead do this? The globe is referred
to as an "Xenophot" globe, if that makes a difference. Thanks for any

Re: Can somebody please explain why..........

They must have taken the lead resistance into consideration when
choosing lamp voltage and must think that a short lead will increase
voltage to the lamp excessively ???

Re: Can somebody please explain why..........

Seems strange in that case as car battery voltages vary considerably from
fully charged (13.8v) to less.
If the spotlight is a 100W than the current drawn from a 12v supply will be
approx 8.3A, obviously more if the voltage is a bit higher.
8A continuous current drain needs a lead with a low resistance.  I can't see
shortening the lead being an issue. ???

Re: Can somebody please explain why..........

The length of the lead forms part of the total circuit resistance and plays
a part in limiting the inrush current at turn on.
The lamp resistance is VERY low when cold so the lead limits that first rush
of current to a level the designer thought was OK.

John G.

Re: Can somebody please explain why..........

"Mark"

** By increasing the voltage getting to the lamp -  silly.

Incandescent lamp life is very strongly affected by voltage  -  eg
increasing the voltage by 10 % above nominal reduces the expected life by a
factor of 3.

To a good approximation, lamp life is inversely proportional to the 12th
power of the operating voltage - provided that voltage is not more than say
25 % above the nominal rating.

.....  Phil

Re: Can somebody please explain why..........

Is it a cheap chinese / taiwanese product where the power lead consists of a
few fine strands of black scale covered copper wire?