Light strength / brightness rating CP or WATTS

[jurgenscraft]

I have often seen spot lights rated in CP , candle power, all I can imagine is the brightness of that particular light, I am familiar with light globes rated in watts from which I can calculated the amps drawn by these particular globes, be it 55 watt or 75 watt or so on, but when a light is measured in CP I have not a clue as to what load a 400,000 or a 1000,000 CP spot light will draw from the battery.Is there a rule of thumb or some form of conversion from CP to watts, that indicates what sort of a load in watts or amps these high power lights draw,<br />Kind Regards,<br />William Wright

 

[ZmOz]

Re: Light strength / brightness rating CP or WATTS

Candlepower is just an inflated marketing gimmick. It's kind of like the horsepower rating on air compressors, they all claim to be 5hp while only drawing enough electricity for 2hp. Several spotlights that use the same 100 watt bulb can vary from 1 million to 10 million CP. I have one of these spotlights that claims 10MCP with a 100 watt bulb, and I have a high end HID spotlight which is rated at "only" 7MCP. This rating is pretty accurate, and it blows away the 10MCP light.

 

[Andrew Leigh]

Re: Light strength / brightness rating CP or WATTS

Hardly,<br /><br />One candela (candlepower) = One Lumen (international Unit of luminosity) whereas watts represents electrical power. One candlepower is the measure of the light from one ordinary wax candle, a measure used for years and on which the lumen is based.<br /><br />An 80W incandescant bulb is no match for a 80W Mecury Vapour lamp in terms of brightness but both absorb / radiate the same amount of power. The colour temperature of the bulb will also affect the brightness.<br /><br />Normally the packaging box will rate the wattage of the light. If it is 120 W @ 12V then expect to draw a current of 10Amps. At 75W then expect to draw 6,25A.<br /><br />If for your boat and make sure that it is a seperate battery else you may find starting difficult with a flat battery.<br /><br />Cheers<br />Andrew<br /><br />That is the theory, of course marketeers may well bend the truth without stating how tests were conducted etc.

 

[ZmOz]

Re: Light strength / brightness rating CP or WATTS

Originally posted by Andrew Leigh:<br />That is the theory, of course marketeers may well bend the truth without stating how tests were conducted etc.

That's exactly the problem. No spotlight available today, except for high end lights, has an accurate CP rating. <br /><br />jurgens craft is comparing the same type of bulbs, so comparing watts is the most accurate way of comparing brightness.

 

[Paul Moir]

Re: Light strength / brightness rating CP or WATTS

Thanks for bringing that to my attention ZmOZ, I had always taken the mfrs numbers at face value. Considering the theoretical maximum efficiency of a light source (any light source) is about 19 candles per watt, it really makes you wonder how they manage to get 10,000,000 out of 100W of power. Especially with an incandescent halogen bulb running around maybe 15% efficiency. <br />Perhaps they are measuring in 'tea-candles'?

 

[Perfidiajoe]

Re: Light strength / brightness rating CP or WATTS

With spot lights there is more to it than that, the concentration of the beam means more than the candlepower. think of a flood light & a spot light rated at the same wattage. There's light & there's useable light. Watts is how much power it will draw, C.P. is the light produced, (by someones measurement I guess)

 

[jlinder]

Re: Light strength / brightness rating CP or WATTS

you're missing the point. CP is a measure of light output, watts is a measure of the power used. They are 2 separate things<br /><br />While the two can often be related, there are a number of factors<br /><br />1. Type of light source. A standard incandescent bulb is about 1% efficient (1% of the energy comes out as light, 99% as heat). Halogen are a little better. Florescent is about 4%. LEDs are abouyt 50%<br /><br />2. Manufacturers measure the light intensity at the brightest spot (center of the beam). Numbers are higher if the beam is tightly focused into a spot.<br /><br />3. Manufacturers are creative with their measurements (lie).

 

[ZmOz]

Re: Light strength / brightness rating CP or WATTS

Originally posted by Jack L:<br /> you're missing the point. CP is a measure of light output, watts is a measure of the power used. They are 2 separate things

But again, I believe the original poster is comparing two lights of the same type, so wattage is a very accurate determination of brightness. If he was comparing a halogen, an HID, and a fluorescent light, obviously watts would mean nothing. All halogen bulbs put out about the same lumens per watt...so more watts = more light and the same watts = same light output.

 

[jurgenscraft]

Re: Light strength / brightness rating CP or WATTS

GENTLEMEN AND LADIES, thank you all for the informative replies, I found them very interesting indeed , Yes Iam comparing two identical types of bulbs same brand name, rated in watts and powered by a 12 volt supply.On the asumption of 19 candels per watt ,as posted in one of the replies I can now calculate the wattage of the light rated in candel power and work out the load in amps.??? I also understand that reflector shape, material and type of bulb/ globe have a effect on brightness etc.but the bottom line is still how many watts devided by volts does a 500,000 CP light draw compared to the run of the mill 55/65 watt sealed beam, eg 500,000 devided by 19 =26315.8 watts this devided by 12 = 2193 amps??? wow , or have I got it all wrong,I suppose the simple thing to do is find some one with one of these lights and put a ammeter in circuit and measure the load,<br />Kind Regards ,<br />William Wright

 

[ZmOz]

Re: Light strength / brightness rating CP or WATTS

Candlepower has nothing to do with amps. Amps = watts divided by volts.

 

[TwoBallScrewBall]

Re: Light strength / brightness rating CP or WATTS

As far as amperage, most of these spot lights use one of the following:<br /><br />A single 55W bulb (about 5A)<br />A single 100W bulb (about 9A)<br />A pair of 55W bulbs (about 10A)<br /><br />Determine what bulb they use (look for replacement specs if all else fails) and you then know the amperage. Nothing more to it. Period. Amen.<br /><br />As far as candlepower. The measurement is, as said above, taken at the brightest possible point. Therefore a spotlight with a super-efficient parabolic reflector that gives you a tight beam over a long distance will have much higher candlepower than a flood light that spreads the same light over a wide area. <br /><br />You're overthinking this. Just step back and look at it again. The amperage has NOTHING to do with cadlepower, ONLY with wattage at the bulb. Candlepower is the magical number that manufacturers give to the 'percieved brightness' of the light. <br /><br />Have fun!!!

 

[TwoBallScrewBall]

Re: Light strength / brightness rating CP or WATTS

ZmOz, you know what they say about great minds.... <br /><br />;D

 

[ZmOz]

Re: Light strength / brightness rating CP or WATTS

Originally posted by Stiff Nibbles:<br /> ZmOz, you know what they say about great minds.... <br /><br />;D

They all eventually go insane?

 

[Peter J Fraser]

Re: Light strength / brightness rating CP or WATTS

If you put a 55 watt bulb into a FLAT reflector you will always have a 55 w bulb but the light is relected all over the planet. About as efficient as a Model T headlanp on 6 volts.<br />Place the same bulb into a properly designed and focussed dish reflector such as for a long range driving lamp and you will see a huge difference in reflected light all in one direction while still only emmitting 55 watts of light.<br />It has not consumed any extra power to do this.<br />Candle power means nothing as has already been stated and is often quoted by manufacturers to suit their own gain.<br />An advertising gimmick at best.<br />If you're curious, compare different lamps and see for your self.<br />Get a Maglight torch and aim the beam at a wall while adjusting the focus and you will see the change in the light pattern, Focus to the brightest spot and then walk towards the wall and observe the change in pattern.<br />Peter

 

[TwoBallScrewBall]

Re: Light strength / brightness rating CP or WATTS

Zm, Yup.

 

[jurgenscraft]

Re: Light strength / brightness rating CP or WATTS

In closing gentelmen, I went down the the local auto electrician and he showed me something very interesting regarding CP versus Watts.He took me over to the store room and took out two boxes containing tail light globes,(brake and rear light), on the one box the first manufacturer rated his globes as 12 volts 21 watts and 5 watts, the other maufacturer rated his globes as follows 12 volts 32 CP and 4 Cp. I then proceeded to make up a quick test circuit with a ammeter in circuit and tested both manufactuter's globes,the results were what I expected, the amperage was virtually the same, so I assume the following that a 100 watt globe emits as much CP as the lamp design allows, ie the reflector design ,the lense design and the type of globe being used etc.I will use the term Watts as a electrical function of the equation and CP as the amount of light being produced by the globe and light combination,that to me is a simplification of the question.seperate the two ratings, thank you very much for all the valuable input,<br />Kind Regards.<br />William Wright