What's the lowest lumen rating that the eye can detect? Less than .003 lumens?

[kaichu dento]

the limit of detection is even smaller if:

the object that is bouncing photons in your direction is moving rapidly across the field of view (about the speed of a tasty rabbit)

you are not looking right at it, rather at the very periphery where your eyesight is the most sensitive

Good point and having thought a good deal about peripheral vision over the years, had never considered differences in light gathering when compared to central vision.

As has been mentioned the human eye is extremely sensitive and the answer to the original question I believe is that the eye is sensitive to any light. It probably isn't possible to come up with some level of light that isn't visible to the human eye.

How right you are! LOL!

I'll make a distinction here since I didn't in the OP - it's usable light projected in the direction of the users interest that I'm concerned with and as such, any light source that won't at least make itself known at a distance of at least a few inches would be useless to me, even if it were visible when viewing the emitter alone.

Last night on the mountain my friend was checking to see how far my V10R and Clicky were at their lowest respective levels and even the .08 of the hCRI Clicky was able to project out to about 30', where I would hope to have it capable of going down to the level that it was usable only at 1' or less. Perfect for looking for something on the nightstand...

The OP poses a great and interesting question. Let me just confound things a bit. When I worked in technical theatre I occasionally had the task of training stagehands (and others in the technical space) how to use dim lights discretely. I found that often students had the required visual acuity to accomplish the task at hand but when they lacked the required concentration they couldn't see anyway.

My point is that there is another issue lurking around these perception issues, and that is that many persons have the visual acuity for a given setting but lack the concentration to be able to use what their eyes are seeing.

These are complicated issues and the answers are rarely as black and white as the would seem at first glance.

This is the most perfect type of response that I'd hoped to see here when I originally started this thread and it is exactly what I've been preaching to what mostly amounted to a brick wall for some time now - everyone can see at virtually the same levels - it's just whether or not their mind is capable of functioning at those levels.

I drive up the mountain on a regular basis at about 10mph in a Sus-V and they have a very low headlisht setting for stealth mode which is perfect for almost all my runs. The only time I turn them on full is when I want to more clearly assess the trail condition in order to speed up if possible, or slow down if necessary.

Most of the other drivers can't believe it when they first start, but once they give it a try they realize that it's way more than bright enough and it also offers a better opportunity for customers to see the sky, rather than just the trail ahead.

It's like running, doesn't really matter unless you do it.

My feelings exactly!

Very interesting subject. From what little I have experienced, beam shape and tint play into what modes I use with lights. I am a neutral/warm fan, but it seems plain white seems to be more effective at the extreme lows.

I wonder how many folks can walk around the house with a Proton Pro on the lowest red. I think that level is best for reading a watch or something real close.

That's one reason I like cooler tints at lower levels quite often but that would be and interesting side point to hear some experiences relating to tint and usability.

 

[Sub_Umbra]

...it is exactly what I've been preaching to what mostly amounted to a brick wall for some time now - everyone can see at virtually the same levels - it's just whether or not their mind is capable of functioning at those levels...

It is a very real phenomena which I believe likely spans all of our senses. I have witnessed this firsthand in a number of disciplines. Since most people are visually oriented lack of concentration is very easy to see in sound operators, for example. (Sorry this doesn't read right, but it's true) In theatre sound operators fail to hear things under stress that they could easily hear if they were in a more relaxed, centered state. This also partially explains why deaf or nearly deaf sound operators continue to keep their jobs -- because though connected, their performance is not limited by their reduced acuity because they are compensating by doing a better job of concentrating.

Just as some doctors were told to take a few deep breaths to get the most info out of viewing an x-ray (an old relaxation technique) I used to tell technicians to take a few deep breaths before a difficult cue to try to relax; to center themselves to try to get themselves into a state where the low-level input would actually register (be it visual or audio).

Ask a police detective about this subject and they will probably tell you that when a witness is afraid or otherwise stressed they often don't remember all that may be expected of them.

Stress and concentration (or the lack thereof) most definitely affect the way we perceive and review lights. I think that Light Culture and concentration are factors we must consider every time we are asked for an opinion on some questions.

Whether it's, "...What light should I get to walk my dog," or, "...What light should I get to navigate the house at night," I have to constantly remind myself that these issues of acuity, concentration and stress are all things that we can not answer about another user and yet without that info the specs of the light in question, or even the opinion on that light from another user are close to worthless.

 

[kaichu dento]

In the ensuing months since the last posts were made we have come to accept that a light like the TC-R1 can be a common commodity and I would guess that the levels of light coming from the emitter at its lowest settings are much lower than the original number posted in the thread title.

Has anyone yet tried to measure the lowest outputs on a TC-R1?

 

[SemiMan]

Just read this thread for the first time.

I am not going to work out the calculations (call me lazy) but this should be an easy research exercise.

1) There are any number of resources, research papers, etc. that discuss not only the detection limits of the human eye, but the minimum light levels required to do certain tasks, descern objects, etc. Those limits will generally be expressed in terms of either candela or surface brightness depending on what is being referenced.

2) From either candela or surface brightness, you can work back using that number and an estimate of surface reflectivity, what the surface lux required is.

3) From the surface lux and an assumption of the beam pattern, you can calculate the needed lumens.

Would be interesting in a spreadsheet and I am sure others (well at least me) would be interested in the results. Swamped these days so I can't take on the exercise of finding the research papers again, but perhaps if someone researched the appropriate papers, someone else could take on the math (or me if you catch me on a good day).


Semiman

 

[ShineOnYouCrazyDiamond]

Pete - you know that I am a low lover like yourself. It is almost a must for any around the house EDC to have a super low low. I sold my LF2XT, as awesome as it was, because it was just way to bright on it's lowest setting.

I was made fun of at one point in the TCR1 thread because I was defending that even when the LED in the TCR1 was too low to be of any use (it's actually possible) it was still perfect for me. It's all good, I opted not to defend my position further as it was a useless battle, but I wasn't offended either.

I have three trits (two orange and one green) set into the base of my TCR1 with Norland and I've spent some time in a pitch black room comparing the lowness of the TCR1 against the three trits. I can say that I have it so that the three trits almost seemed like they were blinding. Although there is no way I could ever navigate a room just with the light of the three trits I can use it to see my hand or anything else within about a 1 foot range. I don't feel it has any practical application but it's just neat to know. Now I don't know if the advertised .003 lumens on the TCR1 is just a number or if there is any validity to it, but I can say that light can definitely go too low to be practical.

I agree with your OP that the lowest low on the HDS lights is ridiculously bright in a dark room, definitely can be too bright. The lowest level on the T1A is really just about perfect - I could use lower but really generally don't need to. I just acquired a TCR2 and while the lowest low on it is way below that of a HDS it is still brighter than the T1A and coulduse to be lower. The only other light I have that can fit this bill are my Spys - my level one setting is always a super dim one - for those who know the Spy UI I have my Tri-V level 1 set to blend the MC-E and XP-G and set it using position 6 and let it drop 38 blinks to find a perfect low.

I don't have any means to perform quantitative testing on the lumens level. But my qualitative judgement based on lights with specified low levels says that less that 0.01 lumens can still be practical for around the house navigation in pitch black.

 

[kaichu dento]

The main shortcoming on the LF2XT is the limited range - could go both higher (a little) and lower (a lot). But I'm still keeping mine for it's great UI and excellent beam pattern.

I've actually decided to use less trits, although they're all the rage these days. Too damn bright for use in conjunction with a couple of my lights that actually go low enough for my satisfaction. My TC-R1 is definitely one light that will go lower than I can possibly use it, which is very relaxing. They just went off the edge of the cliff for low level, and we finally have a light that can satisfy on both ends of the scale, top and bottom. The Spy's are another light that can go lower than anyone could wish for, but I found myself wishing that #3 position could go as low as #1 and #2. After programming the first two spots the way I wanted them, the third setting was too big a jump and I ended up having to compromise. In the end I was pretty well okay with it though.