135 vs 180 lumens, Can I tell the difference (Fenix L2D/LD20)

Will I be able to tell the difference between 135 and 180 lumens, and if yes, is it significant that I should care?
This is regarding the: (Fenix L2D non Q5/LD20 with Q5)

Also, if anyone is looking to buy a light: 4sevens has lights on sale:

Olight T10 - $54.95 $39.00
Olight T15 - $54.95 $45.00
Olight T20 - $63.50 $55.00
Fenix P3D CE - $61.50 $44.96
Fenix L2D CE - $56.50 $41.46
NiteCore D20 - $73.00 $58.40

ps. Just got my first fancy flashlight! (not saying which one, as hopefully not to influence your answer to my original question).

I do already have a Rayovac 3 watt, Inova X0 - which has a dead CR123A, a Inova Bolt, and some random high-power LED flashlights (Coleman, some Home Depot stuff, etc)

The 50 lumens difference will be enough to notice, but thats about it. Won't actually look like that much of a difference. I would guess that you would only be able to tell with the 2 lights side by side.

Looking at the Olight T10 page, while it says "Q5", I think the specs are for the pre-Q5 model, using a lower binned LED.

Which one is on sale, the Q5, or the earlier (2007), non-Q5? Although they are both good lights...the 2008 Q5 is the only T10 that is fully regulated on both 3v primaries and 3.7v rechargeables, AFAIK.

Nice price on the T20, I'm very tempted....

ImGeo said:

Will I be able to tell the difference between 135 and 180 lumens, and if yes, is it significant that I should care?

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Can you tell a difference? Probably, when directly comparing two otherwise identical lights.

Will the difference matter? Of course not, it's not significant in actual use.

The "CE" lights in particular are probably above those minimum specs. Cree hasn't produced a particularly high volume of P4's for quite a while. They are more likely Q2-Q4

If you keep going in 50 lumen increments it will become very noticeable in both directions. My light either lights up what i want it too or it does not. If 130 lumen's is enough for you to do what you want to do then get it but if it leaves you struggling get brighter. For me at night in the hills with no light pollution 5 lumen's is enough to follow a trail but if i need to set camp or break camp quickly i need so much more. For urban use i like 200 + and to feel safe i like 600 in my pocket. On my keyring 10 is plenty.

If the brighter one has a wider beam: no

if really unsure and with a non obvious difference, compare beams:
light up a wall with light one, have light 2 shine at the same spot and move beam of light one away, add beam one again and put beam 2 away ...
do this a few times, the less bright one can be found quickly by doing so.

You won't notice from a few feet away, because the reflected hotspot on both will be enough to max-out your retinas (assuming you're using them in the dark, of course), but you'll notice an increase in throw distance with the brighter one.

Glad I found this thread. I have a new LD20 and I can't tell the difference between high and turbo. I've tried several feet indoors on a white wall and outside in real world use...

floridonet said:

Glad I found this thread. I have a new LD20 and I can't tell the difference between high and turbo. I've tried several feet indoors on a white wall and outside in real world use...

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Hmm...I have the LD20 and want to claim that the difference between high and turbo is clearly noticable, though not perceived as tremendous.
I wonder if you have a faulty light, because when compare side by side or by directly changing the mode the difference between 94 and 180lumens is undoubtly visible.

Regards, patric

The LD10 needs a good eye to see the difference but the LD20 is very clearly brighter.

I have a L1T and LD10 along with a 2AA L2D body.
The beam profile is different enough to make them totally different lights.
I saw a good video on youtube from nutnfancy showing them side by side.

LD20 is brighter but for the price I would take a L2D.
In South Africa the local agent for Fenix has "while stocks last" L1D's for a bargain. (relative to our market of course. You would cry at the $60 price but it sure beats $90+ LD10)

In regards to high vs turbo. I can generally only tell the difference if I go into high and then twist head directly into turbo, it's not a big difference at all.

1. I agree with two posts above: a. if one beam has a large hotspot and the other a small one, you will be able to tell since all the lumens will be concentrated in the small area, and b. you can tell much more clearly when you look at the beam at a distance (throw), since the amount of light is spread out more and smaller differences will be noticeable, particularly at the outer reaches of the beam.

2. I believe it isn't the absolute value of the lumens that counts, i.e the 45 lumens that you mentioned, but the percent change. Thus, an increase in 45 lumens on a base of 135 means that the light output as increased by about 33%. Since the eye can see brightness as the square root of the increase, rather than linearly, that would translate into an approximate increase of 15% in perception of brightness. All other factors being equal (see #1); that probably would be noticeable.

An increase of 45 lumens from 255-295 means an increase of only 17.6% in light output. That would be a perceived increase of approximately less than 9% and probably wouldn't be noticed.

HarveyRich said:

2. I believe it isn't the absolute value of the lumens that counts, i.e the 45 lumens that you mentioned, but the percent change. Thus, an increase in 45 lumens on a base of 135 means that the light output as increased by about 33%. Since the eye can see brightness as the square root of the increase, rather than linearly, that would translate into an approximate increase of 15% in perception of brightness. All other factors being equal (see #1); that probably would be noticeable.

An increase of 45 lumens from 255-295 means an increase of only 17.6% in light output. That would be a perceived increase of approximately less than 9% and probably wouldn't be noticed.

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The amount of increase in stimulus intensity to produce a perceived difference is referred to as the JND for just noticeable difference. It's a foundational concept in the study of sensory perception, and one of the first things I teach in the classes on visual perception and general perception I teach at my university.

The difference is not strictly a ratio (although it's the best heuristic to use to understand the relationship) as that requires a linear scale; perceptual differences work on a log/power scale so as you increase the stimulus intensity, a subsequently greater increase is needed to perceive the next difference.

For example, if I put a 1 lb. weight in your hand and then add another lb. anyone can easily perceive the distance. However, if you're carrying a 50 lb. sack of potatoes and I add 1 lb. to it 99.8% of all people won't be able to tell the difference. You need a much larger increase at that point to be able to notice the weight has changed.

My Quark AA^2 is rated at 70 lumens on "high" and 170 lumens on "turbo". In my experience, when I switch between the two, the difference is noticeable but not great. For my Quark AA the difference is from 70 to 109 and I can still see a difference, but it is much smaller. You should be able to see a significant difference between 135 and 180 although it will vary by individual.

I'd say you should get a light that will give you at least three different brightness levels. That way you can choose the one most appropriate to your need at the time. Terminology aside, I use what I call the "goldilocks" scale; "too low", "too high", and "just right". Of course, what level is what depends on where I'm at and what I'm doing at the time.

I have done several attempts to estimate brightness differences comparing my different lights and comparing their different brightness modes.

While the statement of demanding 4 times the brightness to perceive a doubling sometimes feels very correct, there are situations where this isn't corresponding to my experience.
Some lights and brightness modes feels very different than their actual. When I have compared Fenix L1D between low and medium (12 and 53lm) the difference often feels small, not more than twice. The lightmeter confirm that the stated difference is very fair, though.
But when I tried it with red filter the difference seemed to be several times and corresponding to the actual difference...

With Preon2 the difference feels bigger between the mid and high than between low and mid, though the case is the opposite.
The same it feels when compare the modes of TA30. Though the ratio between the modes is very exactly the same (5times), it feels like the difference between mid and high is bigger. Here I perceive the difference to be bigger when going down from mid to low than going up from low to mid...
If anyone wonder about my statement for TA30 and react about that this doesn't correspond to the stated values of 9, 60 and 225 lumens, I based this number because of the measured difference with lightmeter. Between low and high is very close to 25 times, which is in line to Fenix statements of 9 and 225lm. This means that the actual brightness of mid mode ought to be closer to 45lm than 60, and it's the same with my TK10.

When I compare Fenix TK20 I find the situation to be similar as with Quark 123. If I compare the difference between 45 and 150lm, and between 70 and 170lm I perceive it at least twice, though it's not 4 times.

Comparing Fenix TA30 and TK30 the difference between 225lm and 630 is huge. Though it's not 4 times it feels like more than twice.

Based on my experience I oppose about to consider it as a law that perceived brightness difference is the square root of the actual difference. Sometimes it seems to be correct, sometimes not. Many factors are included in how the eyes perceive the difference, and I can't explain why my eyes sometimes seem to deceive me more than other times...
Therefore I mean a better statement is that the perceived brightness isn't usually proportional to the actual difference, but you cannot set out an exact number, like a law.

Regards, Patric