brightness of 3H and other GID

Someone who has never seen tritium-based lights in action, might be surprised by the weak brightness. Here I'm talking about "illuminators", not the small "locator" trits.

Pictures of such devices will not always give the right message to someone who is not attentively reading complete threads, so I was wondering if there exist better criteria to define the "usefulness" of such lights.

Values such 100-1000 microlamberts don't say much to the uninitiated, and even charts such as e.g. Surelite's do not help a lot.

One poor man's way (i.e. one without light measuring equipment) could be to compare the output to common devices such as eg a Nokia 3310 lighting up in the dark: I tried this with my Torch, and it seems that both produce the same output when at the same distance from a wall - guess this is similar to a ceiling bounce test.

Maybe an improvement is to use well known lights - such as the Nokia - except that not everybody has such a model. Even this comparison is not complete, as it compares two less known items (even the trits are not so known to everybody).

How about following criteria to categorize such lights? Maybe such criteria already exist... This could give a better idea to the interested whether to invest in such lights or not.

1. be able to walk around with the light
2. be able to read a book such as a Penguin Book
3. be able to read a map
4. ...

Another way to put some metric I was thinking of could be based on a variant of a Snellen chart. Any CPF eye care professionals have ideas?

The idea is to have a white sheet of A4 with a grid of (what seems to be called) optotypes with size increasing from top to bottom, and contrast (ink blackness?) increasing from left to right. The top-leftmost character will probably not be readable by anyone, while the bottom-right one will be by everybody.

An attempt with the fonts available here, just to give the idea (imagine random letters lined up in a grid):

qwerty
qwerty
qwerty
qwerty
qwerty
qwerty
qwerty
Edit added: I'll try make such a sheet Monday.

The idea is to report the faintest readable letter in each row.

Maybe three readings could suffice instead: smallest font (highest line), lightest colour (leftmost column), and one in-between (although there's probably no linear relationship between the three points).

The measuring would be in two phases. In a first (reference) phase, the subject performs the test in bright daylight, to get an idea of his/her visual acuity.

Then, the test is repeated with fully adapted night vision, using the device to light the same sheet of paper. I'm sure there will be differences; that could give a good impression on the usable brightness of a device!

Problem with all these approaches are that (IMHO) much depends on the visual acuity of the viewer: someone with bad eyes will report different from someone with excellent eyes, but the reference would give an indication there.

But the main point is to avoid having to judge a light based on pictures, because it is very difficult to take those pics, and IMO such pics can't give a true impression of the value of a light. And the criteria above - if they can be refined - could allow to categorize various GID sources more accurately (other than by lamberts, lumens, or luxes...)

-alex- (somewhat bitten by GID :tinfoil

ps - There is also the "walk to the toilet":toilet: criterion - further subdivided into "crawl to the toilet"...

see also
http://flashlights-axd.wikispaces.com/Betalight
https://www.candlepowerforums.com/threads/159057
http://www.cpfmarketplace.com/mp/showpost.php?p=1142097&postcount=29

Made a first cut of a A4 paper in an attempt to judge the readability under very weak lighting conditions: see this PDF.

Using my Betalight Torch just above the surface of the sheet, I'm able to read the 'E' from column 6/row 7, and the 'R' from column 7/row 6 (and better). Personally this means I cannot read a book, or smaller characters on maps.

When holding the light approx. 20cm away from the sheet, I'm able to read the 'U' of col 5/row 1.

I think I will enlarge the grid, and am considering to use those E symbols found on the real Snellen charts, or Sloan letters. And maybe there should be more diversity in (small) font sizes.

I'm curious to hear from the other Betalight Torch owners what they can read in total darkness; but I'm afraid this kind of test depends too much on the visual acuity of the tester...

-alex-

Edit added: this one rings a bell: http://psych.nyu.edu/pelli/pellirobson/
Edit added: try also to mention the age of your light, maybe also other characteristics. (Eg Luce de Notte owners: sphere diameter, ...))

I bought mine as a nice gadget for the showcase, I haven't tried to actually use it until now... :candle:

Alex, I just got your response PM and, as I said, don't remember hearing of this light as a betalight but ....now, yeah, right on the front----"BETALIGHT TORCH"...Looks as though mine is 965. I too bought it as a novelty light and really haven't put it "through the paces" so to speak....


Karl

I tried the posted PDF with one of (these) 2Ci trit markers. Without night adapted eyes, but holding it close (~1cm from the sheet) I could make out column 9 from rows 1-4, column 8 from rows 5-8 and column 7 from row 9.

The test is still a little subjective (to eyesight, printer, etc.), but it's the best I've seen so far for such low output levels. :twothumbs

I think there will be a difference with night-adapted vision. But your measure is already impressive... (and way much better than mine - though we are talking about a different light), that makes I need to expand the chart to even smaller values.

Maybe something like a Unihedron Sky Quality Meter could be used to quantify output from such low intensity light sources?

Does anyone own one?