Lux, Lumens and stuff

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Mick F
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Lux, Lumens and stuff

Post by Mick F »

I received a new torch from Father Christmas, it's fantastic!
www.ledlenser.co.uk
http://www.ledlenser.co.uk/Product_D_Pr ... hFocus.asp is mine.

SOOOOO bright! it's rated at 60 lumens, powered by 3 AAA batteries, it is lightweight and handy, and fits in my pocket easily. Wow! This sort of brightness was only available if you had a huge battery-powered lantern. In the past, I'd discovered Maglites. Fantastic, but heavy and battery consumptive with their halogen bulbs.

Now we have LEDs and superb lenses - Maglite are getting left behind. I drool at the idea of having some hi-tech lighting for the bike, but have no use for it as I don't commute any more, riding only for pleasure. I now look up Lux and Lumens and Candela, terms that until recently, I had never heard of.

I reckon that Lux is the best measurement, coz it takes into account the useable focused light cast out onto the road.

Am I right?
Mick F. Cornwall
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paulah
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Post by paulah »

That's what I understood when I was looking for a new bike light. Lux is the lumens per squre meter.

The most useless measurement is candlepower - lumens per square foot - my old cateye has a high candlepower (1000+) but it's mostly concentrated in a very small area, totally useless for spotting potholes in the dark unless you're doing about 4mph with the beam directed right in front of the wheel. Lux does at least guarantee a wider beam.
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robwa10
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Post by robwa10 »

paulah wrote:The most useless measurement is candlepower


I think you're point is proved not only by your old cateye but also by the fact that most lights that give their data in candlepower usually get poor reviews. Companies figured out that if they could put a big number by the tech data then people would be more likely to buy it. I nearly bought a Sun light that boasted a 1000 candlepower until I read a review that said it was good if streetlights were around.

A question I had when looking for a light to use on dark lanes...
Is there any way of comparing or converting the different definitions? How many lumens are equal to lux, or candelas and so forth?

Mick, do you reckon you could mount the new light to the bike easily? And how good do you think it would be on dark lanes?
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Coffee
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Re: Lux, Lumens and stuff

Post by Coffee »

Mick F wrote:I received a new torch from Father Christmas, it's fantastic!
www.ledlenser.co.uk
http://www.ledlenser.co.uk/Product_D_Pr ... hFocus.asp is mine.



Mick, did you have the Tesco torch? I'm wondering how they compare, must be a bonus being able to adjust focus.
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paulah
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Post by paulah »

robwa10 wrote:A question I had when looking for a light to use on dark lanes...
Is there any way of comparing or converting the different definitions? How many lumens are equal to lux, or candelas and so forth?


Not really - 2 lights with say 100 lumens could have different lux, or 2 torches with different lumens could have the same lux, it all depends on how wide the useful part of the beam is. Same goes for candlepower - it can't be converted to lux without testing the torch because the beam could be just wide enough to cover the square foot or it could be the same brightness over a square meter.

Going off a review or recommendation is probably the safest bet, and avoid candlepower - as you said it seems to be used mostly to make lights with poor beam quality sound impressive.
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Post by willem jongman »

See http://www.peterwhitecycles.com/headlights.asp for excellent beamshots of nearly all interesting lights. The only light missing in this lineup is the new B&M Cyo, which in a sense occupies the spot between the Fly and the Edelux. It comes in two flavours, one for more light nearby, and one for more light in the distance.
Willem
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meic
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Post by meic »

Looks like a nice light. it is a lower power LED than the Tesco 3W Cree.
However look at the max. battery life 50hrs compared to 2hrs, because it can be put on lower settings.
Also it has an adjustable beam pattern.
I think it would work nicely with the Tesco torch. Leaving this on all the time and using the Tesco when you want Full power.
Yma o Hyd
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andrew_s
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Post by andrew_s »

I look for more lumens. That's the "amount of light", and offers little scope for artificially big numbers

Lux is how brightly something is lit, and can be manipulated by either putting the something closer to the lamp, or by having the lamp concentrate more of its light into a narrower beam. It's saving grace is that German road regulations specify how it should be tested, and German lights quoting it can be compared (probably).

Candlepower is beam intensity (lumens per steradian). It's independent of distance, but can still be inflated by using a narrow beam.

. oooOOOooo

If Mick F thinks his LED Lenser is good, I've got a Fenix L0D on my keyring that gives 75 lumen off 1xAAA. It doesn't last all that long on full power, but still does well enough that I cycled 20 miles of unlit country lanes using it once, by way of experimentation.
rogerzilla
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Post by rogerzilla »

It's all marketing lies, usually.

Here are some actual light tests.

http://yacf.co.uk/forum/index.php?topic=11751.0
kwackers
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Post by kwackers »

rogerzilla wrote:It's all marketing lies, usually.

Here are some actual light tests.

http://yacf.co.uk/forum/index.php?topic=11751.0



Good resource!

I was quite excited by the look of the Lupine Betty 6 on there - until I saw the price!

Does beg the question whether it's ok to directly compare a Hope LED 1 (£70) with the Lupine (£550)
Perhaps a better comparison would be 7 Hopes (and some change). :lol:
DavidT
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Post by DavidT »

[quote="robwa10A question I had when looking for a light to use on dark lanes...
Is there any way of comparing or converting the different definitions? How many lumens are equal to lux, or candelas and so forth?
[/quote]

I looked into this during the course of last year, and basically gave up, and had to go for a lie down in a dark room (pun intended).

I love this sort of thread, but I think the answer to this question is something of a holy grail? Until such time as the manufacturer's agree on declaring a stated specification, I think we are left to experimenting in darkened lanes, and reading reviews from our mates on forums like this?
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Mick F
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Post by Mick F »

DavidT wrote: I think the answer to this question is something of a holy grail? Until such time as the manufacturer's agree on declaring a stated specification, I think we are left to experimenting in darkened lanes, and reading reviews from our mates on forums like this?


My thoughts entirely.

It just seems that Lux has it for me at the moment, though my torch lights up the lane to a Wow! degree.

No, I didn't buy the Tesco 3w jobby, Coffee.
The variable focus system works well-ish, but in 'wide' there's nearly a hole in the centre of the beam. On 'spot' it just Wow!

If I tied it to the bike, I reckon it would be quite a bit better than I ever rode with back in the old days when I commuted at 6.30 on a winter's morning. The main difference would be that when I had a bright Xenon front light, I'd wear out a set of rechargeable batteries on the way to work - 1 hour. I'd recharge them for the way home in the evening. Eventually, I bought a second set, and took a fully charged pair in with me for the way home. Later, I bought a Soubitez BB dynamo - fantastic!

LEDs have transformed the bike lighting market. Batteries last 100s of hours rather than 100s of minutes, and far brighter and better lenses than only 15 years ago could have even contemplated. We never had to work out the figures in any system before, bright was bright. Good was good and Xenon or Halogen was as good as you could get.
Mick F. Cornwall
willem jongman
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Post by willem jongman »

Interesting tests, but I cannot escape the impression that there is considerable measurement error involved. Look at the measurements for the IQ Fly, the Cyo and the Edelux. They all use the same reflector, and yet the measurements for centre and off centre are quite different. Equally, these measurements suggest that the E3 is more focussed than the Edelux, whereas everybody else says the opposite. Finally, how come the Cyo is brighter than the Edelux? That is hard to believe.
The good news is that we have come a long way. Led lights and superb optics have joined forces to give us really good lights, and I am sure they will only get better.
Willem
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andrew_s
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Post by andrew_s »

Mick F wrote:LEDs have transformed the bike lighting market. Batteries last 100s of hours

No they don't.
An AA has enough energy in it to drive a 3W LED for about an hour, so 2xAA = 2h max at full power, 4xAA = 4h max at full power. It's less if you allow for regulator inefficiency, not being able to get the last bit of energy out etc.
Cateye etc can only quote the long run times they do because most of the time the lights are very much dimmer than the fresh battery brightness they quote.
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paulah
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Post by paulah »

kwackers wrote:Does beg the question whether it's ok to directly compare a Hope LED 1 (£70) with the Lupine (£550)
Perhaps a better comparison would be 7 Hopes (and some change). :lol:


I got a hope after it had been recommended here a couple of times, have used it on lit streets and unlit potholed lanes and am very happy with it. Possibly the only upgrade needed would be another one so I can point one at potholes even further ahead.
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