Lumens/Candlepower

Surf-Matt

Just looking at the possibility of getting a new front light - noticed that high end lights are generally expressed in Lumens but cheaper ones are usually in candlepower.

Googling tells me 1 candlepower = 12.57 lumens but a few calculations show this to be pretty daft.

Why is there the difference and can anyone tell me how many lumens 15,000 candlepower is/are?!!

cee

you cant as a candlepower is not a real scientific unit.....

you could use the candela as a replacement, but any calculations are going to be inaccurate.

mostly again from googling, clicky

The comments at the bottom are the good explanation about why you can't really compare them, and why manufacturers of cheaper lights might use candlepower to make the lights sound brighter, especially as most candlepower references seem to be about peak beam, which is subjective and thus not really quantifiable.

Surf-Matt

Hmmm - but I was hoping to find a very rough calculation.

Just looked at the top Cateye light (triple shot) rated at about 800 lumens. The website says it's 30,000 candlepower - so more or less 37.5 candlepower per lumen.

Just looking at the EL610 plus - 15,000 candlepower (which could be 400ish lumens?) for a pretty good price (from the right shop), rechargeable and compact - could be a goer.

I'm sure they are not directly comparable but it's annoying that two different standards are used!

stumpyjon

I did the same search as you a couple of weeks ago and couldn't get my head around the conversion 1 candlepower = 12.57 Lumens??

That means my Cateye EL530 at 1500 candlepower should have a lumen value of 18855 which compared to a top of the range Lupine Wilma at 920 lumens just doesn't make sense.

I also read that you can't actually convert one to the other very reliably as they are really two different measurements, candlepower is a measure of how bright the bulb is at source and lumens is a meaure of how much light is reflected back. I think it's all down to beam spread from an MTB perspecitve. My Cateye light is very bright but is very very focused so doesn't illuminate much.

omegas

I have used the Cateye EL610 plus and found the opposite to Stumpyjon that it is bright but has a wide spread of light. I used it with a Smart Polaris 3 LED that has a narrow spot beam and it worked well on unlit pathways and country roads. The output from them both was about equal only one cost around £70 and the other £15.

I have also found that a Bikehut light I have at 650 lumens is as good as the Cateye 610 that claims 1500 lumens.

If you can use a friends lights or try a few out on late opening at a shop as what manufactures claim and what you get can be very different.

There has been a lot of lights threads on the forum the last few weeks but the more you read the more confusing it all becomes.

supersonic

Lumens represents the total luminous flux of the lamp (basically light ouput).

Candle power represents the concentration of light (lumens per steradian). A steridian is a measure of solid angle (imagine a cone, where the lamp is at the tip).

Imagine a laser beam - many you can buy use an LED, but the lumen output is very small. But as the beam is incredibly narrow, the candlepower rating is high! This is a good example of how the lumen and candle power measurments are not direct.

Now imagine a naked flame burning. It is emitting light in all directions and not concentrated or focused, not a narrow beam, so its candela rating is going to be lower. If it is emmiting 1 candela in all directions (over basically a sphere), its total light output in lumens is 4pi x the candela rating, which is 12.57 as there are 4pi steradians in a sphere. If you block half the light ie so it shines on just one half of the inside of the sphere, its candela rating is still one (the focus or concentration has not changed per unit solid angle) but the light output has, so it will be 6.3 lumens.

How does this relate to bike lights? Lumens is the only way to compare. As can be seen from the above, a candela rating is very dependant on the focus of the beam and can be artifically made to look higher. Plus it shows no indication of how wide that beam is.

artillerydave

supersonic wrote:

Lumens represents the total luminous flux of the lamp (basically light ouput).

Candle power represents the concentration of light (lumens per steradian). A steridian is a measure of solid angle (imagine a cone, where the lamp is at the tip).

Imagine a laser beam - many you can buy use an LED, but the lumen output is very small. But as the beam is incredibly narrow, the candlepower rating is high! This is a good example of how the lumen and candle power measurments are not direct.

Now imagine a naked flame burning. It is emitting light in all directions and not concentrated or focused, not a narrow beam, so its candela rating is going to be lower. If it is emmiting 1 candela in all directions (over basically a sphere), its total light output in lumens is 4pi x the candela rating, which is 12.57 as there are 4pi steradians in a sphere. If you block half the light ie so it shines on just one half of the inside of the sphere, its candela rating is still one (the focus or concentration has not changed per unit solid angle) but the light output has, so it will be 6.3 lumens.

How does this relate to bike lights? Lumens is the only way to compare. As can be seen from the above, a candela rating is very dependant on the focus of the beam and can be artifically made to look higher. Plus it shows no indication of how wide that beam is.

:shock: ?

supersonic

If you concentrate the output of a bulb, its candle power rating increases. That is because it is shining that light over a smaller angle.

So if you buy a light purely on the candle power rating, you have no idea of how bright the original bulb is as you don't know the angle!

The best bike lights are ones where you know the output of the bulb (the higher the lumen rating the better), and can change the beam spread.

FSR_XC

Matt

PM'd you

Surf-Matt

Mark - are you sure? Not got one coming up!

My stupidly basic understanding is that candlepower is the the light outputs, lumens is what actually "illuminates" the surrounding. But it would be handy to know roughly what this means.

Yes there have been a zillion light threads but each one seems to claim a certain light is better! It's one of those things I just can't justify shelling out hundreds for but if I can get something half decent for not too much, I am willing to give it a go.

Almost £800 for a Lupine just doesn't compute in my small brain though... :shock:

supersonic

No, the lumen represents the light output! Candlepower is lumens / angle (in steradians).

Again, imagine a laser beam. Low lumens, high candlepower due to very narrow angle.

FSR_XC

Matt, give me chance to write it!

S_J_P

There was a really good site I used to use for comparing lamps torches and the like which explained all this, and gave his own measurements. I'll see whether I can find it...

Here it is FlashlightReviews. The author explains how he actually measures output and throw in relatively lay-speak.

artillerydave

supersonic wrote:

If you concentrate the output of a bulb, its candle power rating increases. That is because it is shining that light over a smaller angle.

So if you buy a light purely on the candle power rating, you have no idea of how bright the original bulb is as you don't know the angle!

The best bike lights are ones where you know the output of the bulb (the higher the lumen rating the better), and can change the beam spread.

:?

I use the attach to bike on a dark night and go riding and if you can see stuff it is bright enough method to measure my lumen output.

seriously though in my club the lights used on our evening rides range from cateyes, dinottes, hope and exposures and they all do an excellent job. not too much between any of them really.

stumpyjon

I suppose as a rule of thumb anything rated in candlepower (such as my Cateye) whilst strictly speaking is not lying is probably big up the light. If you want a genuinely capable light you would expect the manufacturer to rate it in lumens. Lumens as Matt says is more a measurement of the amount of light returned by the what ever is being lit where as candle power is a measurement of how bright the light source is at a given point from the bulb / LED. When rating my light I expect Cateye put the detector in the centre of the beam and surprise surprise it was very high, make the same measurement off the centre and the candle power will be significantly down. Do the same with a Lupine Wilma and the candle power will be high over quite a large beam angle.

More confusion to be found here lumens.htmlhttp://www.theledlight.com/lumens.html

supersonic

I think that site confuses it even more!

Lumens is the TOTAL light that falls on the detector. It measures all the light the source produces.

Candela is the light per unit angle.

A high candle power rating is not much use if the beam it produces is the size of a coin at 20 yards! If the beam is the size of a garage door at the same distance, much better! But the candle power rating is still the same. However in the latter, the lumens is higher as the total output is higher.

Good point about that some beams spreads are not even though.

rd350lc

supersonic,
How the hell do you know so much .........I cant even read what you have written above let alone understand it, you need to get a girlfriend bad !!!.

Lol

Rich

supersonic

To the first part - I dunno!

To the second part - yep!

medicineman

So how does this relate to Watt output for an LED?

supersonic

Watt is a poor way to compare lamps. Different lamps have different efficiencies - so the brightness can vary drastically for a given wattage.

rnm

Hi,

Regarding bike lights, and now that everybody can understand that candles as a measure is just rubbish, the most important is to think in advance on the use you want to give it…

If you just need something to make your presence noted, on bike path for example, a safety light (even those that sell them self in candles…) is more than enough… (Here in Portugal they can be found in Chinese stores for 1.5 £). If you also want to see were you are going, then make a better search on the web…and dig into tech specs! Good lights require battery power, and old Nickel Cadmium (NiCd), Nickel Metal Hydride (NiMH) or Lead-acid storage battery all have their advantages or (in some cases more) disadvantages. But like in cell phones, Li-Ion technology is now available. Less weight, affordable (sometimes) and it can be recharged anytime without loosing charging capacity. It’s also important to understand how fast you will ride depending on your light… Light intensity behaves logarithmic… You loose ¼ of the intensity every time you double the beam range (Since the light spreads for 4 times more area, like speedlight flash intensity.)… If this means that you don’t see were you are going, let me give you 2 advices: ride slowly and buy a better light!

I have a Sigma PowerLed Black Edition. Probably it’s a bit big, but it can be used as a hand torch, works both with AA batteries and with IION Li-Ion battery pack and there’s more than enough power for a serious night ride if you like… It costs a bit, but only 1/3 or 1/6 of the “pro” systems of Blackburn, Cateye, or Lupine… (Obviously that a Lupine Betty 14 is always on my wishing list, but unless it fall’s from heaven I do not allowed my self to have a bike light that costs 3 times the price of my bicycle…!)

I’ve used for my evening rides, and charge it less than once per week…! It’s great (and looks nice also!)…

Ricardo

P.S. have you all notice that serious lighting systems always refer to “W“ instead of Lumens, Candles or Lux?
8)

speedkingsox

Ok, Watts (sic) brighter on the road : a 1500 candlepower Cateye HL-EL530 (which i currently own) or a 240 Lumens Hope Vision 1 LED (which i'd maybe consider adding to the Cateye)?


SOX!
Team Madigan

supersonic

Without knowing beam angles and beam distribution it is impossible to tell, unless someone has them.

Also see the What Lights sticky.

delcol

i just so happen to have both...

i prefare the hope over the cateye, i would say the cateye throws the beam further but the hope has far better spread.. togeather they should be an awesome pairing.. for road....
my cateye broke the grove underneith were it clips into the braket craked and broke. was riding to work and it just fell off in the middle of the road and the magnetic switch fell off, wouldn't work,,

Northwind

You should google for Rhod Gilbert's rant on the million candle power torch... It won't answer your question, but it's very funny.

Anonymous

this is quite a simple explanation which helped me figure it all out

Dazzza

Lets just have it nice and simple, just ignore candle power and just look at the lumens figure, that gives you your total light output, stop trying to confuse matters by going all technical, threads like this have been done to death on candlepower forums.

The lupine is a poor example anyway, they advertise 1300 lumens when in reality it's more like 900 actual, same for the p7 torch, 900 lumens when it's more like 6/700.

One of the few lights i've seen to be right is lumicycle, it's rated at 1120 lumens and uses 4xr2 emitters that kick out 250lm each so 1000 lumen total, but on boost mode they're overvolted from 1a to 1.2a hence why you get a bit more.

Matt give me how much you want to spend and what you're after and i'll do my best to look for what is best out there.

Can't say fairer than that now can we.

supersonic

Daz, you seen the age of the thread ;-).

I hope our sticky solves most of this lol.

Dazzza

Oh haha, well if it helps i've been in plymouth all day having the car remapped and will soon be heading riding out now it's cooler, im bound to be a bit slow today give me some credit.

delcol

what car you got dazza..

Dazzza

94 subaru wrx, emissions were high last year and i had a niggly deadspot, turned out to be a shagged lambda sensor.

anyway bit lower power than i expected she's 307.7hp and a very odd 323lb/ft of torque, should be the other way round id have thought but im happy.