The Lumix/Candles/Watts conundrum

pinno

Yes I know this should be in Workshop or something - I don't care :P

Can someone explain the relative brightness of the different measurements of output. Is there a conversion table ?
My 2 Smart lunars are one and a half and two and a half watts (respectively) output and they're pretty good.

PS I am planning a raid on Aggies basement.

team47b

P(W) = ΦV(lm) / η(lm/W)

team47b

oh I forgot you'll need this bit too

The power P in watts (W) is equal to the luminous flux ΦV in lumens (lm), divided by the luminous efficacy η in lumens per watt (lm/W)

pinno

Just had a look at this:

The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source. Luminous flux differs from power (radiant flux) in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light, while radiant flux measurements indicate the total power of all light emitted, independent of the eye's ability to perceive it.

Okay Team47b smarty Portugese pants, here is a question for you - why don't manufacturers stick to a standard method of measurement ? After all, as a consumer we need to have a yard stick or should I say Lumen Beam, to help make the comparison between one set of lights to another. So your equation is not going to help me decide.
Is there a direct comparison between Lux and watts ?

team47b

Sorry, I was havin a larf.

You can only compare the brightness of the various light sources on the market by knowing the number of lumens they produce to use as a standard measuring device. You can make a comparison by finding out the lumens per watt, standard light bulbs are about 12 lumens per watt, LED about 40 lpw, strip lights about 60 lpw.

They should of course just tell us how bright it is compared to a 60w bulb cos we all know how bright that is, lumens are based on candle power but I think a candle would just blow out on a bike in the weather you're having!

pinno

team47b wrote:

Sorry, I was havin a larf.

...LED about 40 lpw...

Are you sure ? I built a 1/32 scale racing circuit for my neices. The LED's I used were between 10,000 and 17,000 millicandles. In fact, the range of LED's is huge.

Cleat Eastwood

team47b wrote:

P(W) = ΦV(lm) / η(lm/W)

If you do that backwards you create dark.

Its actually the formula for Stoke.

pinno

Cleat Eastwood wrote:

team47b wrote:

P(W) = ΦV(lm) / η(lm/W)

If you do that backwards you create dark.

Its actually the formula for Stoke.

The Dark is the place where you do most of your misdameanors with CB and Stoke is probably the best place to do it 'cos no one would bat an eyelid there. So don't knock it. (Dodgy doings of a sexual nature by cyclists is called 'clunging', for those not in the know.)

team47b

You are right, I went to Stoke, twice, it was dark both times, I will recalculate the formula.

pinno

I have been to Manchester a few times unfortunately. It was always raining. Whats the formula for rain in Manchester ?
Thankfully I haven't been to Manchester in the dark so I cannot compare it with Stoke.

Still raining here...oops, Warning thread crossover thread crossover.

Gizmodo

The formula for rain in Manchester is 2rA^n (where rA is the rain fall in Anglesey and n is the number of bikes you own).

The best way of improving your bike light efficiency is to move South to somewhere like Portugal like Team47b, Scotland is so far North that you won't see the sun again now until April (if you're lucky).

Edit: it's still better than Stoke where you can see the Sun but only if you buy it from a newsagent.

pinno

For Cleat and Claire Balding

On this thread; wondering if I can save on batteries by moving to Portugal. Don't think i could put up with the constant adulation of that greasy spick Ronaldo.

Whats the formula to decide whether its worth moving or not ?

team47b

Sr Ron lives in Spain.

Formula:

Give up work @50 + 350 Days pa sunshine = Smug barsteward

carrock

pinarello001 wrote:

Just had a look at this:

The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source. Luminous flux differs from power (radiant flux) in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light, while radiant flux measurements indicate the total power of all light emitted, independent of the eye's ability to perceive it.

Okay Team47b smarty Portugese pants, here is a question for you - why don't manufacturers stick to a standard method of measurement ? After all, as a consumer we need to have a yard stick or should I say Lumen Beam, to help make the comparison between one set of lights to another. So your equation is not going to help me decide.
Is there a direct comparison between Lux and watts ?

To be fair the decent manufacturers do all list output in lumens. The ones who advertise candelas or whatever do so to hide the fact that their rubbish light puts out about 50 lumens. As a rule of thumb, buy something that puts out at least 400 lumens and it will be bright enough

pinno

carrock wrote:

To be fair the decent manufacturers do all list output in lumens. The ones who advertise candelas or whatever do so to hide the fact that their rubbish light puts out about 50 lumens. As a rule of thumb, buy something that puts out at least 400 lumens and it will be bright enough

Listen Carrock mate, that sensible logical stuff really wasn't in the spirit of things. Now I am going to have to warn you. This is your first cautionable offence and I am punishing you with this:

Take that and don't do it again

freddiegrubb

Anyone for the inverse square law of illumination?

Cleat Eastwood

freddiegrubb wrote:

Anyone for the inverse square law of illumination?

That would be R+R+aR +Ar+ R+r+ar+r = this

carrock

pinarello001 wrote:

carrock wrote:

To be fair the decent manufacturers do all list output in lumens. The ones who advertise candelas or whatever do so to hide the fact that their rubbish light puts out about 50 lumens. As a rule of thumb, buy something that puts out at least 400 lumens and it will be bright enough

Listen Carrock mate, that sensible logical stuff really wasn't in the spirit of things. Now I am going to have to warn you. This is your first cautionable offence and I am punishing you with this:

Take that and don't do it again

Ah yes thought I was in Workshop for a minute there....

team47b

the answer is 4100 lumens!

http://www.wickedlasers.com/torch

fit this puppy to your bike, set fire to communters/peds/cars etc

Nick Fitt

Does the density of darkness enter into this anywhere?

Cleat Eastwood

Also, if nobody has actually weighed it - why is called light?

freddiegrubb

On a serious note , a couple of years ago I watched a series of progs. on light, it started with the musings of various bods hundreds of years ago with associated very simple maths. As the series went on the musings & maths got longer & more intense, till in the end the blackboard ( it must have been 4 metres long ) was covered in calcs. & they admitted they still don't truly know.