Head Torches

[StarryEyes]

I have been looking at many different head torches that have a red function and I was thinking of getting this

Petzl Zipka Plus 2 Head Torch Review

But I'm a bit confused, does anyone know about head torches and the difference between burn time and battery life. I thought they were the same but if you look at the features list at the bottom of this review it has different figures for both things. So I understand what battery life is but what is burn time and why is it different to battery life?

Thanks in advance

[RobSay]

I don't think there is any real standardisation in torch terminology but in the case of Petzl, they do have a definition and I think they're trying to help. My reading of it is that it is the length of time the torch will give out at least 0.25 lux at 2m (1 lux is 1 lumen per sq m)

(Petzl requirements | Petzl). 0.25 lux is Petzls definition of the limit of usability. It will almost certainly be tested and measured with white light.

With LED lights you get a rapid drop off of luminousity over the lifetime of the battery. Initially it is very bright but this fades quite fast - I very rarely get to the stage of LED bulbs going out before replacing batteries and the replacement is always noticeable. I probably instinctively use the 'burn time' and not the 'battery life'

When going out winter climbing I will invariably make sure I have new batteries on me. The faded light of old batteries really is significant. This is less important for astronomy where you actually want lower light levels (even in red). You also don't tend need the throw of a full high intensity beam for long distance viewing which eats up power.

140hrs is a lot for something that size.

HTH

Rob

[Horus]

I use a Petzl , had it 6 months and still havnt changed the batts

[brianb]

My reading of it is that it is the length of time the torch will give out at least 0.25 lux at 2m

Well, battery life is meaningless unless the temperature is specified ... batteries will go dead very quicky at low temperatures & miraculously recover if they're warmed up. Normal alkaline batteries have an almost zero life at -20C.

[RobSay]

Well, battery life is meaningless unless the temperature is specified ... batteries will go dead very quicky at low temperatures & miraculously recover if they're warmed up. Normal alkaline batteries have an almost zero life at -20C.

Very true. I have on one occasion stuffed batteries in an armpit to warm them and headtorches/phones routinely go in the sleeping bag when out in winter!

Any way back to Petzl: "These tests are first carried out at an ambient temperature of 20 °C, and then at extreme temperatures between -30 °C and +60 °C."

Which almost helps .. except that they still only give one figure at the end. If the 140hrs was measured at 20°C then it's optimistic - when is it ever this temperature when it's dark in the UK!

[StarryEyes]

Thanks everyone and thanks Rob for the explanation, it makes sense now.