Nits vs Lux

[inteller]

I got a handy 5 in 1 multimeter for Christmas to measure nuisances.  it measures lux, but I was mainly interested in measuring nits from all of the glaring LED signs popping up everywhere (since that is how they are regulated).  Does anyone know what the difference is between nit and lux as far as being able to convert between the two?

[cannon_fodder]

These physics geeks seem to know:
http://www.physicsforums.com/showthread.php?t=188801

Apparently nits depend on distance and light source size in addition to intensity... so there are different variables.  Apparently.  I won't pretend to actually know.

This website has equations and explanations for each...
http://hyperphysics.phy-astr.gsu.edu/Hbase/vision/areance.html

No short answer I'm afraid.

[Red Arrow]

quote:Originally posted by inteller

I got a handy 5 in 1 multimeter for Christmas to measure nuisances.  it measures lux, but I was mainly interested in measuring nits from all of the glaring LED signs popping up everywhere (since that is how they are regulated).  Does anyone know what the difference is between nit and lux as far as being able to convert between the two?

That's the first multimeter I've heard of that measures light. Where did you get it?

My dad used to have a light meter for photography before cameras all had built in light meters.  I think my sister got the light meter when dad passed away.

[patric]

quote:Originally posted by inteller

I got a handy 5 in 1 multimeter for Christmas to measure nuisances.  it measures lux, but I was mainly interested in measuring nits from all of the glaring LED signs popping up everywhere (since that is how they are regulated).  Does anyone know what the difference is between nit and lux as far as being able to convert between the two?

"Nits" is an obsolete lighting term that was a synonym for "Candellas per Square Meter" or (cd/m²).  For some reason the sign industry has chosen the obscure metric for it's new technology, but cd/m² is always used to describe the brightness of video screens and LEDs.  

"Lux" is the Euro equivalent of the American "Footcandle" measurement of light.  For rough calculations, 1 Footcandle = 10 Lux (just move the decimal point)

Lux is lumens per square meter, as opposed to
Footcandle which is lumens per square foot.

Nits or cd/m² is a measurement of Luminance, where
Lux or Footcandles is a measure of Illuminance.
Luminance is light emitted from a given area, where Illuminance is a measure of light striking a surface.

Are we having fun yet?

Since the relationship between Lux and 'Nits' is derivative, it might help to look over the page at:  http://en.wikipedia.org/wiki/Lux

Speaking of obscure, sign-industry-written zoning code in Tulsa allows billboards to be lit to 70 footcandles, but gives no method as to where or how that is to be measured, so there is no enforcement.  When you consider ONE footcandle is roughly the light on the street surface directly underneath a residential streetlight, you can see there is a lot of slop in the way we light things.

Just for fun, take an illuminance meter to your local gas station for some real mind-blowing numbers.    

[Red Arrow]

quote:Originally posted by inteller

well, I think from a light pollution perspective, it isn't up to the sign industry to choose what measurement they want to use.  They are going to choose the one that benefits them the most.  In fact, it sounds like they have been jacking around with numbers and terminology to come up with a unit of measurement that suits them.  The science behind the measurement is sound, but I don't think the applicability is.  When light is shining into my eyeball and blinding me, I want to measure the light at my eyeball, not at the "source".

and what is the dwell timefor signs here in the city?  The one I'm looking at right now seems to have about an 8 second dwell time.  I thought it was 12 seconds.

I guess we could nit-pick (pun intended) about what units to use but measuring at the emitting surface makes sense.  There is a LED sign in Jenks (Sonic, I think) that is bright from a distance but intolerable up close. Measuring the Luminance and regulating that will eliminate the question of how far away to measure Illuminance (using Patric's definitions.)  Lower Luminance at the surface  will result in lower Illuminance at any distance.

[patric]

quote:Originally posted by cannon_fodder

No short answer I'm afraid.

The short answer is that the ordinance was written in such a way that no one standing on the ground could verify compliance.

[patric]

quote:Originally posted by inteller

what is the dwell timefor signs here in the city?  The one I'm looking at right now seems to have about an 8 second dwell time.  I thought it was 12 seconds.

A couple of well-funded council candidates re-wrote the proposed ordinance after taking office to raise the intensity levels and decrease the message time to 8 seconds... and they also built in a loophole of one second between messages where anything goes.

[cannon_fodder]

quote:Originally posted by inteller


And BTW, why are you giving Luke and Matthew such even odds?  My bookie has Luke as a 15:1 longshot.

First person to comment on it.  Congrats.  They are the Christmas stories having Jesus born in Bethlehem and Nazareth, respectively.  I've always found it amusing that the Christmas story is out of Luke, and the other gospels either disagree or don't think it is a big deal.  Luke being a second hand Gospel account (most agree it mirrors and embellishes Matthew) written some 80+ years after the fact.

I take great exception to ye' ole' Christmas story as historic fact on many levels: to start with Jesus was not descended from David per the gospel itself, the census was not called by Augustus and was not empire wide [it was a Syrian census called by the governor, technically], the census that was called was in 6 A.D., after Herods death (not "in the reign of King Herod), non-citizens were not part of the census,  citizens were counted were they lived - not the home of their ancestor 1,000 years ago, animals slept inside the homes of most farmers - a "manger" would have been the ground floor with the animals not an outbuilding, and the star, the kings, and the prophesies were wholeheartedly stolen from previous cults and just to make it fun... most of our "traditions" are were also adopted by Christians for ease of use from pagans.  At least, those are my preliminary problems with the story.

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