Caving - How many Lumen for a light is enough?

[royfellows]

I have to confess that I had actually being considering an 8,000 lumen lamp to offer for sale.

Basically following my existing methodology, 4S XML2s for beams, same again for floods, running off a 16V power pack 3P X 4S 18650 Li Ions. Power pack would have inbuilt charging control electronics, charging being done off a laptop charger.

The stopper on it was the realisation that having to use small reflectors it would not really be any better than the latest X6000 which has improved reflector setup, and the really big question of what use is such a thing.
Not dead in the water though.

I once produced a 6,000 lumen experimental lamp which was all beams, 6 Crees sitting behind 6 reflectors, no floods. This was just for the fun of it.
Took it up to Nenthead and lit up the whole Nent valley!

 

[Mr Mike]

You probably set the locals off.... 'strange lights in them hills' accompanied by a howling.

 

[royfellows]

You probably set the locals off.... 'strange lights in them hills' accompanied by a howling.

UFO phenomena

 

[Roger W]

But - by the sound of it - definitely too much light for working in a constricted dig, sitting down having a break with your mates or even walking through a reasonable sized passage.  OK for those huge dark chambers in Welsh slate mines, I should think, or illuminating some of those enormous chambers they have down on Mendip.

But how many lumens - or, maybe I should say, how bright a light - do you really need for ordinary caving?  I suspect that many cavers today would not be happy with the level of lighting that previous generations had to make do with. 

Oh, and as no-one else seems to have mentioned it - a head lamp is much better than a hand torch.  You can go caving with a hand torch at a pinch - I have done so - but it can be uncomfortable holding the torch in your teeth for any length of time when you need both hands free...

 

[royfellows]

Fair comment Roger, but it was just an experiment
Production models have full range of different light levels, down to a 'moonlight mode' on low flood. Standard beam is about 200 lumens for about 1.3 watts battery hit, plus 3 day or 7 day pilots.

 

[Roger W]

Fair comment Roger, but it was just an experiment

And a very good one too, Roy!  Don't get me wrong - I'm not criticising your high-power lamps at all!

Production models have full range of different light levels, down to a 'moonlight mode' on low flood. Standard beam is about 200 lumens for about 1.3 watts battery hit, plus 3 day or 7 day pilots.

I guess 200 lumens sounds reasonable for general use...?

 

[David Rose]

How many lumens were the old premier carbide stinkies? Or even the Petzl generator carbides running with a reasonable flame? Having returned to deep Picos caving after a 23 year gap in 2009, the weirdest thing for me has been having so much extra illumination. Going back down Pozu del Xitu (first explored 1979 - 81) also made me realise two things: how much we used to miss through being in relative darkness, and the scale of the risks we used to take stepping over very deep holes without any rigging, because back then, we couldn't see the bottom.

 

[potholer]

When I started making LED lights over a decade ago with early Luxeon LEDs, they maxed out at ~20lm for the flood and spot LEDs, and the 20lm spot was more than enough to light up deep pitches on expeditions to Slovenia which had seemed far less scary previously when using carbide or a handful of 5mm LEDs.

And while it wasn't really usable for things like moving across the odd boulder floor at decent speed, a 2lm 'naked' flood LED was actually pretty adequate for the great bulk of the caving out there, generally vertical work and small-ish passage.

As for a Petzl carbide, I used to run a Laser headset with a 14l jet off a [good and suitably fettled] Fisma, and typically ran it fairly low - I'd often get a decent 8+hrs and still have meaningful carbide left, but I could turn it up even fairly late in the day and get decent light when I needed it.

Being essentially a pure flood, it would take a lot of lumens to light much up at a distance, but that's still the case.
Looking at a ~1000lm pure flood from naked LEDs on one of the Scurion clone lights in Slovenia a week ago, it didn't have much distance performance, and [gratifyingly] my ~300lm flood LED with a bit of gentle forward biasing gave it a run for its money, showing again that beamshape is as important as lumens when it comes to usefulness.

If I had any carbide left, I'd be tempted to fire up the old setup and see what lightmeter readings I'd get off it compared with an LED light on flood.
And for all the numerous advantages of LEDs, I do still miss clamping a hot Fisma between my thighs if I'm sitting somewhere freezing my nuts off waiting for someone to put a bolt in.
Sure, carbide did take a little work, but having a good Fisma when other people were trying to get Arianes to behave was a constant source of entertainment.

 

[David Rose]

Back in the day we used to use them for lighting cigarettes, too. Not a lot of smoking going on underground nowadays!

 

[bograt]

Just been playing with solar panels and LED lights on a totally caving unrelated project, thought I'd do a quick experiment;

Maximum voltage produced by domestic LED down lights in darkened room using same 12volt power source and same solar panel -

Rated 230 lumens - 9.37v
Rated 320 lumens - 10.36v

So it looks like there is a correlation, about 1v per 100 lumens?

Must admit, this is only a 'seat of the pants' backroom experiment but could be a precursor for further research?

Interesting to note that the solar panel used is rated at 12volts in full daylight, so it would appear that the 320lumen lamp is about 80% daylight at around 1metre distance.

 

[ChrisJC]

I'm not sure I follow your experiment.

But the lumens output of an LED is very non linear when measured with respect to voltage. For example, going between 1 & 2 volts will produce no real difference in output (it will be off), 2 to 3 volts will come on, and 3 to 4 volts will make it as bright as the sun, then expire.

Chris.

 

[DavidGibson]

Just been playing with solar panels and LED lights on a totally caving unrelated project, thought I'd do a quick experiment;

Maximum voltage produced by domestic LED down lights in darkened room using same 12volt power source and same solar panel -

Rated 230 lumens - 9.37v
Rated 320 lumens - 10.36v

So it looks like there is a correlation, about 1v per 100 lumens?

Must admit, this is only a 'seat of the pants' backroom experiment but could be a precursor for further research?

Interesting to note that the solar panel used is rated at 12volts in full daylight, so it would appear that the 320lumen lamp is about 80% daylight at around 1metre distance.

Unfortunately, youre barking up the wrong tree   Solar panels do not - emphatically DO NOT - generate "voltage", they generate "current". The current is directly proportional  to the illumination. If you do not "do something" with the current, it flows through the parasitic diodes inside the panel and generates a voltage, but the voltage across a diode is proportional to the logarithm of the current - that is, it is not a linear relationship . If you want to use a solar panel to measure illumination you must contrive to measure the short circuit current, not the open-circuit voltage!  Use a meter to measure the short-circuit current whilst, at the same time, using another meter to measure the voltage, checking that it is "well below" the open-circuit voltage. That will confirm to you that you are measuring the short-circuit current. (A short circuit will not damage the panel because its producing the current anyway - the panel doesnt "care" where the current goes).

When a panel is "rated" with a voltage, its got little to do with how much voltage they produce - because it is current that they produce, not voltage. Its an indication of the size of the parasitic diode array and a warning that the panel cannot supply current at a higher voltage than that, because it would all flow in the parasitic diodes instead of in the load.

 

[bograt]

Surely PD (voltage) is an indication of Current?, otherwise could you give us a definition of current that does not include the term 'voltage' or 'potential difference'?.

I was merely suggesting that for differences in light intensity a solar panel could be a useful measuring device--

Theory has its place but I am a 'hands on' bloke--

 

[potholer]

Cheap luxmeters are available from about ?15 upwards, which do measure fairly accurately over a wide range of light levels (probably more accurately than anything most people could cobble together).

And to measure lumens still needs some mechanism to eliminate the effects of beam-shape, unless comparing lamps with identical beamshape.