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Old 06-30-09, 06:54 PM   #1
bktourer1
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Question Watts,lumens,candelpower oh my!

I'm looking for a new light for touring (around $50) and get confused with what to go by, lumens,
candlepower or watts. Is there any easy way on how to figure out what to go by?
I currently use a Cateye with a mini halogen bulb. the shipping for replacement bulb costs
more than the bulb.

Thanks
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Old 06-30-09, 07:23 PM   #2
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so lumens is the same as candle power. 1 lumen is equal to one candle. on the road i'd say 100lumens would be the bare miniume. peferably 200 lumens flashing, moreso on tours on unfimlar roads with cars going fast. secondly you'll see a light to see with. a flashing light is a be seen light, it tells motorist that something is there, a light on soild(not flahing) helps them gage the distance and speed, and lets you see the road, wet leaves, wet paint, pot holes, ect. imo you need atleast 400lumens for this.

a Q5 is an ideal cheap light for commuting(20bucks), but not so great for tours since the battery dies after two hours of flashing. a P7 is again a great cheap light to see all the details in the road. (40 bucks) but dies after 1 hour on high or 2.5hours on med. what you need is lights that last a long while or recharges by genterating power from your hub. there are cheaper, 50dollar ones that use magnets connected to spokes and frame that generate electrciety. but the ones that go into the hubs are better, but cost alot more and the whole hub/wheel will need to be rebuilt. and you'll be looking at 150bucks.

btw watts is the amount of power an object uses, not how bright something is. i can have two 40 watt bulbs and one can be almsot twice as bright, but both require the same amount of energy to power.

links to lights i use on my commute:
http://www.dealextreme.com/details.dx/sku.10727
http://www.dealextreme.com/details.dx/sku.12060
http://www.dealextreme.com/details.dx/sku.20333

Last edited by weavers; 06-30-09 at 07:27 PM.
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Old 06-30-09, 08:38 PM   #3
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Lumens are not the same as candlepower (or candela, the modern equiv.) They measure different things.

If you want to know what each unit is, look at the wikipedia page on each.

Or, in a nutshell ...

Candela gives the light emitted in a specific direction, adjusted for how sensitive the eye is to the frequencies emitted.
Lumens are like candela, including being adjusted for eye sensitivity, but it's about *total* light -- not how tightly it's aimed.
Watts are a measure of how much power is consumed -- how fast your batteries will die.

For bike lights, lumens are the most useful unit to look at. If you make your light have a higher candela rating by using a better mirror to focus it into a better beam, that may or may not be more useful than the original light. But adding more light (lumens) -- that's more universally useful.

Last edited by dougmc; 06-30-09 at 08:43 PM.
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Old 07-01-09, 06:33 AM   #4
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If you're into practical, and for touring that seems to be the norm, then go get a standard battery operated handheld flashlight. Like maybe this one from Sears

http://www.sears.com/shc/s/p_10153_1...ord=flashlight
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Old 07-01-09, 06:54 AM   #5
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If the light is rated in candlepower, it usually means it's a cheaper, lower brightness "see me" light instead of a "see the road" light.
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Old 07-01-09, 09:46 AM   #6
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I've got to agree with the guy deleting my files -- if the light gives you a rating in candlepower, it's probably not very good. Especially if they give their rating *only* in candlepower.

Ultimately, the light with the highest candela rating is probably a green laser. But it wouldn't make a very effective bike light, would it?

If the light only gives you a rating in watts, then it could go either way -- it depends on how efficient the light is. 3 watt lights can vary by a factor of 10 how much actual they emit, for example.

Good lights generally give their lumen rating.
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Old 07-07-09, 05:00 PM   #7
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Here's another term to muddy up the waters: LUX. What is lux in comparison to lumens? I saw a German bike light company use lux but not any other term.
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Old 07-07-09, 05:58 PM   #8
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Lux is how bright the road is illuminated.

From wikipedia
Lux versus lumen
The difference between the lux and the lumen is that the lux takes into account the area over which the luminous flux is spread. A flux of 1,000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1,000 lux. However, the same 1,000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.
Achieving an illuminance of 500 lux might be possible in a home kitchen with a single fluorescent light fixture with an output of 12,000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same level of lux requires a greater number of lumens.
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Old 07-09-09, 07:59 AM   #9
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Lux is probably the rating we really want, especially if we say how many lux are needed in critical areas of the field of view.
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Old 07-09-09, 09:58 AM   #10
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Originally Posted by Road Fan View Post
Lux is probably the rating we really want, especially if we say how many lux are needed in critical areas of the field of view.
And again, a green laser will have the highest lux rating of all as it illuminates it's single square milimeter or so ever so brightly.

Lux ratings are increased by focusing your beam more tightly. But it certainly can be focused too tightly, and `critical areas of the field of view' is extremely subjective.

Of course, straight lumens aren't all good either, as a light could have no reflector at all and emit light in all directions -- it could have a high lumen rating, but wouldn't light up the road particularly effectively, and indeed would blind you as well.

Ultimately, there is no single number that gives `goodness' of a light, at least for our purposes. But if the beam pattern is good, then total lumens is probably the best available. (Though lux would be fine too, as long as the beam pattern is good.)

But whatever you use, be aware that different things are being measured, so you can't directly compare lux, lumen, watt and candela values to each other -- you have to compare lux to lux, lumen to lumen, etc.
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Old 07-09-09, 08:27 PM   #11
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Quote:
Originally Posted by dougmc View Post
And again, a green laser will have the highest lux rating of all as it illuminates it's single square milimeter or so ever so brightly.

Lux ratings are increased by focusing your beam more tightly. But it certainly can be focused too tightly, and `critical areas of the field of view' is extremely subjective.

Of course, straight lumens aren't all good either, as a light could have no reflector at all and emit light in all directions -- it could have a high lumen rating, but wouldn't light up the road particularly effectively, and indeed would blind you as well.

Ultimately, there is no single number that gives `goodness' of a light, at least for our purposes. But if the beam pattern is good, then total lumens is probably the best available. (Though lux would be fine too, as long as the beam pattern is good.)

But whatever you use, be aware that different things are being measured, so you can't directly compare lux, lumen, watt and candela values to each other -- you have to compare lux to lux, lumen to lumen, etc.
Correct, there is no single number. If you can get hold of the SAE, EU, ISO, or US standards for automotive headlights, it will become painfully complex. Light distribution, wavelength distribution, and the minimum required intensities (lux) at a large number of specified critical location are all controlled by the standards.

Most of the ratings we've seen in cycling, including the sole use of lux, are not ultimately useful. The use cases for cycle headlamps are just about the same as for automotive headlamps: see, be seen, urban/rural, see signs, don't cause excessive glare, see pedestrians, see obstacles, et cetera. The main differences are that the speeds are less, the headlight can swing back and forth very quickly, and there is an option for a supplemental "pointing" lamp, such as a helmet-mounted pencil beam. This is both a plus and a minus, tending to cause glare, and enabling pinpoint observation of points of interest.
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Old 07-09-09, 08:44 PM   #12
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Actually a lux reading and a decent beamshot will give you a very good idea of how well the light performs.
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Old 07-11-09, 02:50 PM   #13
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Thanks all. Now that I'm more horribly confused, I won't ride in the dark.
Maybe I need some one running in front of me with a spotlight to light the way
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Old 07-11-09, 05:58 PM   #14
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If you're looking for a simple specification that tells you if a light is worth buying or is suitable to your needs, then you are right to be confused, because such a simple rating is not available. Plus, the true specs are complex, and interpreting them can be a challenge even to engineers.

There are a lot of good reviews here and on the web, in some cases with photos of road illumination. These are pretty darn concrete comparisons, and are probably your best source of information.

Products that can be evaluated based on specs (such as cars and audio equipment) are based on standardized specifications, where there is consistency between what the different manufacturers say. So far that's not the case for bike lights, except perhaps in Germany.
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