Offroad Lights

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

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 worth).  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.

Candlepower

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. *

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. *

Lumen

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

With 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. 

The 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 target area.  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 the market.

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