Following on for the UKC/UKH Headtorches tested article, Martin Bergerud from Lyon Equipment sent this article to help explain some of the technical information behind Reactive lighting and burn time.
Headtorch performance, and the associated figures, is something of a minefield and it's not easy for reviewers and end users to wade through all the information and make an informed decision.
So to burn times. The big issue here is: what is a burn time? For years manufacturers have been free to decide how to record and measure burn times as there is no International standard. A number of years ago Petzl decided to define where they felt light output stopped being usable, as there were some crazy burn times being thrown around. Their baseline equated to the light given by a full moon - approximately a 2-metre beam. So once light output is lower than this they stop recording, even though the torch is still giving out some light.
Next, even though there are these burn times (measured using standard Alkaline batteries recorded normally at room temperature 20C), as they weaken so does the beam. For example the Tikka XP states a max lumens of 80, and a max burn time of 190hrs. This doesn't mean the output is 80 lumens for 190 hours. They are 2 extremes of performance. Standard headtorches with non-regulated output have a common trait: the greater the initial brightness, the faster it decreases.
So the next development to avoid this rapid decrease, and to stabilize the output was Constant Lighting (often known as Regulated Lighting). The advantage of this is that you will have the same quantity of light at the beginning of an activity as at the end.
Then with all this technology and developments in LEDs and batteries, we as the end user wanted brighter torches but with good, if not better burn times.
This is where Petzl's Reactive Lighting comes in, designed to offer the best of both worlds; a bright torch but a decent burn time.
With the Petzl NAO, the company gave out two figures in Reactive mode: a burn time high at 4hrs 40min, and low at 8 hours. With Petzl's OS software you can change the torch performance to burn brighter for a shorter time, or burn longer with less output.
Not everyone wants to do this, however, so for the new TIKKA R-series they felt it was best to quote the minimum burn times that reactive lighting would give out. The problem is that there are no similar headtorches to compare to, so they are out on their own.
So to the main question of reactive lighting and burn times. Some may say that the quoted 10 hours minimum "is really short". Well this depends on how you look at it, as in Reactive that minimum 10 hours allows the torch to give out 80 lumens whenever it wants - even at 9.5 hours - with a 70m beam.
You can connect a TIKKA R to a laptop using the same OS software and extend, for example, to 24 hours minimum with max 17 lumens, 32 metres. It will last longer if the full 17 lumens isn't used, and then go to a reserve mode of 1hr 25mins.
Below are some comparisons amongst Petzl torches to give a feel of what the TIKKA R offers over older models.
In constant mode, the TIKKA R gives 45 lumens and a 25m beam - mainly the flood mode - for 10 hours, and performance isn't affected as much by the cold due to the Lithium battery.
The current MYO RXP programmed at level 5 (a constant mode) would give 45 lumens and a 50m beam for 5.5 hours. This figure would be adversely affected in cold weather if using Alkaline batteries.
The TIKKA XP on standard lighting, after 10 hours use, is giving out a 22m beam which equates to approximately 23 lumens. Again, like the Myo RXP, if it was cold below 5C this would be reduced.
The conclusion is still that it's confusing for all. But to try and put it in a sentence: Reactive lighting is offering power with usable burn times. Our understanding of burn time and brightness as a whole is fogged by too many variables out there, and Petzl is trying to be up front with what is actually going on.
Concerning comments we've seen about Reactive lighting and its reaction to mist, heavy snow and reflective clothing etc. - yes this can cause it to 'flicker' as the sensor is quite sensitive, however you can always select Constant mode to alleviate this issue.
Finally remember you can buy spare lithium batteries for the TIKKA R - everyone should carry spare batteries no matter what torch they use - and there is also an adapter system available that allows you to use AAAs in a TIKKA R. It doesn't allow the Reactive lighting to work, but gives 70% of the Constant figures and makes the torch usable anywhere in the world.
Petzl has information on how torch figures are reached or measured here on www.petzl.com and there will be more in the new year.
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