UKH

Hi...I bought a super cheapo LED head torch off Amazon for general use. Compared to my Petzl Tikka, the light the cheap torch emits seems much brighter. But unlike the Tikka, the 'cheap' light doesn't 'penetrate' at all: if I look down at something in my hand, it's super bright. But if I look at, say, a wall just a couple of metres away, it's as if the light has melted away and illumination is really poor. What's going on? Is this summat to do with Lumens vs Lux? If so, what's the 'take home' when choosing bike lights to see and be seen, and head torches for mountain use?

Cheers

In reply to Kean:

I find the lense shape and focusing has more of an impact than the light output.

Mainly this is from bike lights,  I have done a few look and see visual experiments with the different lights with a mate when it riding and the lense pattern is way more significant.  I have a relatively low lumen single headlamp that has about double the distance of a different nearly 3 times brighter (lumens) lamp. All due to the lense. Much less light overall from the little light but it shines a lot further. 

It all depends on what you want but the headline lumen value is generally not that useful ime

In reply to Kean:

1 Lux is 1 Lumen per square metre. So lumens is the total output of the torch but lux is the actual light you get at the working plane, the working plane varies for head torches as you could be looking at something 1m away or 100m away, also how focussed the beam of light is makes a difference as you could have a little light of a big area or a lot of light focussed in a small area.

In reply to Kean:

Not able to comment on everything but from what I understand (which could well be wrong), Lumens measure the total amount of light outputted, whereas Lux measures the number of Lumens in a given area. If you have a high Lumen head lamp, but with low lux, it means the light is spread out over a large area and therefore not nearly as intense. High Lux would imply that the light is concentrated onto a small area and therefore more intense and penetrating.

I think candela would also be a useful measurement, though it isn't always provided, as it measures the amount of light within the beam angle.

In reply to Kean:

I think this could only be because the beam of the cheap torch has a wider angle so that the photons are more thinly dispersed beyond a certain distance despite there being more of them. This will be due to the shape of the mirror behind the bulb.

I find the Lens to be of great importance to usable light. If the Lens has a diffuser it feels brighter as it spreads out over a larger area compared to a spotlight. 
 

For example I find the Swift RL feels brighter than the NAO RL in open spaces as it diffuses the light better, whereas in small spaces the NAO feels brighter

In reply to Kean:

Cheers all for your replies. So looks like it's the lens of the cheap torch spreading the light over a wider area. So great for close-up work, not great for yomping up mountains at stupid-o'-clock!

In reply to Kean:

My Petzl Actik has two white LEDs, the lens for the low output one diffuses the light, ideal for reading and around camp etc, whereas the higher power LED is more focussed to give more light at a distance, but in a narrower beam.

On low setting, only the diffised LED comes on, whereas on medium and high, both come on, giving the best of both worlds.

Output is 350 lumens, which I find perfectly adequate when out on my local hill for an evening dog walk. Remember that all other things being equal, more lumens equals shorter battery life, and that range is proportional to the square root of the lumen output.

In reply to WildAboutWalking:

Is it just my overly high expectations or has the ideal headtorch not yet been made?

All I think would be needed is one with a simple on/off switch on top, a rotating dimmer switch on one side, and a rotating focus adjuster on the other. Then you'd have complete flexibility in directly as much light as you choose to however narrow a beam you choose, without having to put up with some manufacturer's guess as to what you might want.

I appreciatre that achieving continually variable focus might be a challenge, but surely not beyond the wit of designers?

In reply to john arran:

Like the petzl zoom, but with more output than an IKEA tea-light?

In reply to Robert Durran:

Things were simple with incandescent bulbs where light from the point source filament could easily be focussed into a beam by a parabolic mirror behind the bulb. LEDs are panels facing forwards so a parabolic mirror would not work. A sophisticated lens is needed instead. Cheaper LEDs need a larger surface area for the same light output compared to more expensive LEDs making it even more difficult for a lens to focus the light into a beam.

In reply to Andy Hardy:

at one time you were able to buy LED bulbs for the classic Petzl zoom head lamp that used the flat 4.5 V flat battery. The LED bulbs were quite expensive because they incorporated a miniature glass lens to focus the output. Modern LED head torches are a lot better

In reply to kevin stephens:

In lighting there are a few more concepts.

Lamp lumens - output from bulb

Light output ratio - useful Vs lost light

Luminaire lumens - output from fitting 

If you have a poor fitting you can put a high lumen bulb in it, but due to the low output ratio of the fitting, get a low level of light out.

As detailed by others, the focus will then determine the illuminance.

In reply to john arran:

 I've got a couple of cheap headtorches that work like quite like that. There's a focus adjuster on the light but the dimmer is a lever on the battery pack.  I think they're a LED lenser clone.

In reply to Kean:

As always, it depends.

If I'm in a group, I'll have it on low, as there is a lot of light pollution from the others. You can see any big holes and its enough to avoid tripping over, but it saves power. When running on my own I'll have it on medium, as I can see 10m ahead which is plenty. I only ever use full power, if I need to find a style across a field. Mountain bikers need to see further ahead, so tend to go for more power.

I know people who have a cheapo high power led, focusable torch, as their second light. They use that for long distance style finding, and save batteries on their head torch.

But dont forget the psychological boost you get by turning the light up full, if your tired. Its also good for the comedy Scooby Doo effect. Where you shine your torch on a hill side, and see lots of green eyes reflecting back at you, from the sheep.

In reply to Kean: A great feature of modern LED head torches is the red light option so you don’t lose your night vision whilst still being able to use a map and compass.

In reply to mik82:

I had one of those, I think it was from Aldi. It was great when it worked but after a while it became a bit intermittent, as in sometimes it would come on and sometimes it wouldn't. For a while shaking it would encourage it to work but after while even that didn't do the trick.

In reply to pec:

Mine were from ebay - £7 a few years ago.

In reply to dread-i:>

You hope

In reply to nufkin:

A while ago I was wandering back in the dark from the Kirkstile Inn to Buttermere along the west side of Crummock Water and had temporarily mislaid the path. Fortunately the sheep were faintly luminescent in the starlight and led me back on track!

In my happy state I fantasised that they did it deliberately, but perhaps they were running from my green glowing eyes

In reply to nufkin:

Only the other day I watched (for first time in a LONG time) American Werewolf in London. They have yellow eyes, the green ones are fine.

Anyway as long as you're careful on the moors at night when walking back from a pint at "The slaughtered Lamb", stay near the road and be careful of the full moon it'll be fine. I mean... what's the worst that could happen??

In reply to john arran:

Any focus adjustment mechanism is likely to be a point of failure, as is any rotating control (potentiometer). My only gripe (minor) about the Petkl Actik is that the push button control is not the most intuitive, perhaps trying to do too much with one button, which controls the red LED as well as the two white LEDs. In other respects, it is as near perfect for my needs as I can reasonably expect, and Petzls appear to be indestructible, a very important feature in a headtorch.