Hey Jon!
Hopefully I can get you back on track. I am consulting my physics book to
help us.
Watts are a measure of energy. Candlepower is a measure of luminance (how
much light). You are trying to compare two different types of measurements.
There is probably a correlation between the two, but I can not find anything
here.
Definition: Electrical power is the rate at which electrical energy is
produced or used. Electrical power is the product of the current in the
device and the fall of potential between its terminals.
Watts are measured by the following formulas:
1) P=V*I where P=watts, V=volts, *=multiplied by, I=amps
2) P=I^2*R where P=watts, I=amps, ^2=the value of amps squared, and
R=resistance measured in ohms (Ohms are the same measurement used for
speakers)
3) P=V^2/R where P=watts, V=volts ^2=the value of volts squared, /=divided
by, R=resistance measured in ohms
Definition: The luminous intensity of any other point source of light is
found by comparison. A point source for many purposes can be an ordinary
incandescent bulb if you are not too close to it.
Amount of light is measured by: 1 candle = 1 candlepower - 0.981 cd
(candela). The SI unit system (metric) uses white hot molten platinum as 1
cd.
Candela is measured by placing a photocell above the standard source. The
standard source is then replaced by the unknown source. If the photocell
response is twice as large, we know the luminous intensity of the unknown is
2 cd.
Most light sources have different luminous intensities in different
directions. For example, the photocell aimed at the end of a light bulb will
read a different value than when aided at the side of the bulb. These lights
you are considering are typically measured using an average of the luminous
intensity in all directions, not just straight on.
*** End of lecture ***
What you need to verify is how fast these lights use the energy, how many
amps they use. The alternators are rated by how many amps they create. If
you use more amps than are produced, you will drain the battery which is not
a good thing ;^P Once you know the amps of these lights, you will be able to
size the wire to handle the total amount of amps for all of the lights you
want to use. Wire is rated by how much amperage it can handle safely without
melting the insulation (very bad!!). You will probably want to run these
lamps to a separate fuse as well based on how much amps and how many you
want to run.
Sorry for the long post all! I think this discussion warranted it. It is not
a simple answer. HTH!!
Sean
'92 RC Sport 3.9L 5spd - 250,000mi!
'01 CC SLT+ 4.7L 5spd 3.92 LSD Mobil-1!
-----Original Message-----
From: jon@dakota-truck.net [mailto:jon@dakota-truck.net]
Sent: Tuesday, April 10, 2001 8:13 PM
To: dakota-truck-moderator@bent.twistedbits.net
Subject: DML: Wattage vs candlepower?
I'm a bit confused about wattage vs. candlepower when referring to lights.
There doesn't seem to be a correlation between the two. I'm eventually
planning to build a "roll bar / light bar" for my 4x4 Ram, and I'd like to
mount some lights on the top. The brighter the better. However, this is a
low
buck effort. :-) A little while back, I saw some of those handheld
spotlights that plug into the cigarette lighter at Wal-Mart. They had a
handle
that was just held on with a bolt and a butterfly nut, so it would be real
easy
to mount them on a light bar. They had 1 million candlepower, and were less
than $10 each. Unfortunately, by the time I decided to give it a try, they
were gone. :-( I figured I could have 4 million candlepower (4 lights)
which
would be "really really bright". I may be missing something though, like
the
effect that would have on my alternator? The "standard" lights you see
mounted
on prerunner bars and light bars are wimpy in comparison. Well, most don't
give a candlepower rating, just wattage, but I've seen some of them in use
and
no way do they have 1 million candlepower. Plus, they cost anywhere from
$40-
$200, and more, I'm sure. I just want a lot of light without spending a
lot
of cash...
Stupid idea, or could it work?
---Jon-
.---- Jon Steiger ----- jon@dakota-truck.net or jon@twistedbits.net ------. | Affiliations: AOPA, DoD, EAA, NMA, NRA, SPA, USUA; Rec & UL Pilot - SEL | | '92 Ram 150 4x4 V8, '96 Dakota V8, '96 Intruder 1400, '96 FireFly 447 | `------------------------------ http://www.cs.fredonia.edu/~stei0302/ ----'
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