Converting Candlepower to Watts and vice-versa
& Other Offroad Light Information
Some light sources such as flashlights and offroad floodlights or auxiliary
lights are rated in various different units, such as candlepower or watts. To be
able to compare different types of light sources, it would be necessary to
convert between these types of units when a rating of both candlepower and watts
are not given.
So now the question is how do you convert between candlepower and watts?
The short answer is, you cannot. Unless the manufacturer already has calculated
both candlepower and watts, you're pretty much out of luck. Watts and
candlepower are two very different measurements. Explaining watts and
candlepower help to provide the reason.
Watts is a measurement of
the current draw. A watt is the unit of electrical power equal to 1 ampere (amp)
under a pressure of 1 volt. (Its also equal to 1/746 horsepower for what it's
Amperes are the rate at which electricity flows through a wire or piece of
machinery. A good analogy is water through plumbing. When you open a faucet on
a sink, water flows out at a
certain rate. The same thing occurs when you turn on an auxiliary light. Electricity
flows at a certain rate. This is amperes. Watts are the amount of energy a
device uses in performing its function. To get watts, you multiply volts x amps.
For example, a typical set of offroad auxiliary lights might draw
about 4.6 amps. 12 volts x 4.6 amps = 55.2 watts. To get
amperes, divide watts by volts. Examples: 55 watt auxiliary lights would
calculate like this: 55 watts / 12 volts = 4.58 amps. In the
home a 100 watt light bulb would calculate this way: 100 watts / 120
volts= 0.833 amps.
One candlepower is the radiating power of a light with the intensity of one
candle. This unit is considered obsolete as it was replaced by the candela in
1948, though it is still in common use. 1 candlepower is equal to about
0.981 candela. *
The standard unit for measuring the intensity of light. The candela is defined
to be the luminous intensity of a light source producing single-frequency light
at a frequency of 540 terahertz (THz) with a power of
1/683 watt per steradian, or 18.3988 milliwatts over a complete sphere centered
at the light source. *
The standard unit for measuring the flux of a light being produced by a light
source. One lumen represents the total flux of light emitted, equal to the
intensity in candelas multiplied by the solid angle in steradians
(1/(4.pi) of a sphere) into which the light is emitted. *
* source: Russ Rowlett at unc.edu
Offroad lights different light sources could have the same power requirements, but vastly
different light output. The primary factor of candlepower are the bulb
itself. The light itself is then influenced by the reflector
placed behind the bulb, reflecting the light outward towards the target
area. The brighter and more efficient the bulb is the more light
it will produce using less energy. When a bulb produces light,
some of the energy is wasted by producing heat. The more efficient
a bulb is at creating light, the less heat it will produce. An LED
light (light emitting diode) are a prime examples of efficiently
generating light with very little energy wasted as heat. Therefore
LED lights consume a less amount of energy then incandescent bulbs.
However LEDs are not high light producers when compared to other bulbs
typically used in offroad lights. Typically
Quartz Xenon bulbs and standard halogen bulbs are used.
reflector's role is to "reflect" the light generated by the bulb.
Most of the light projected from an offroad auxiliary light is actually
from the back and sides of the bulb and not projected directly from the
bulb itself. Therefore the better the design of the reflector the
more light will be reflected outward towards the target area. With
the reflector size matters. The larger the reflective area of a
light, the more light will be reflected out towards the
The shape of the reflector is also important. A well engineered
reflector will produce a desirable spread of light on the area in front
of it. The shape of the area can differ from manufacturer to
manufacturer. Some manufacturers design into the light reflector
the means to change the focal length so you can change the spread of
light from a more point point to a flood of light. Because light
from a bulb emits in all directions, the more efficient design of a
light is a broad, somewhat deep circle shaped reflector. The least
efficient is the small egg shape or rectangle lights that reflect less
light. With the reflector, the reflective surface should reflect
as much light as possible with a mirror like finish and deteriorated
reflectors will obviously have a negative effect on the light emitted.
A good set of offroad lights will have a combination of the best
factors, a highly efficient, very bright bulb and a large, broad,
weather tight reflector.
Reviews can be good sources of information to get opinions on popular
offroad lights as well as new lights as they become available on
More Offroad Light Information: