Just what do people mean by "brightness"?

Just what do people mean by \"brightness\"?

I often see people talking about, or asking about, "brightness" of lights. It is not always clear what is meant as I don't think brightness is a recognized photometric term. What does brightness mean to you? Do you mean intensity [think candela], total flux [think lumens], or something else? To understand the above, if you think a focusable Maglight gets "brighter" if you focus to a tight spot then brightness = intensity to you. If you don't think it gets brighter then brightness [probably] = total flux to you.

Re: Just what do people mean by \"brightness\"?

i usaly talk about it in terms of lux or throw i realy like a light to have a lot of throw

Re: Just what do people mean by \"brightness\"?

BRIGHTNESS is how the eye/brain perceives light. The eye/brain does not care about Fc, LUX, Cd, Lu etc., only how dim or bright a light appears to the observer.

Re: Just what do people mean by \"brightness\"?

[ QUOTE ]
Roy said:
BRIGHTNESS is how the eye/brain perceives light. The eye/brain does not care about Fc, LUX, Cd, Lu etc., only how dim or bright a light appears to the observer.

[/ QUOTE ]
I think I understand. By this definition brightness isn't an inherent property of the light at all since wearing sunglasses would make it less bright.

Re: Just what do people mean by \"brightness\"?

seems to have always pertained to the itensity to me. like when we look at the sun and say "ooh, that's bright" we're talking about intensity, hence lux or throw. but i find alot of people here refer to overall light/lumens? as "brightness". /ubbthreads/images/graemlins/confused.gif i think this confuses alot of people when they are trying to get opinions and reviews on lights...........

Re: Just what do people mean by \"brightness\"?

Hello Doug,

My definition depends on wether you are using the light to illuminate something, or someone is shinning the light in your eyes.

A light shinning in your eyes is brighter if it causes you to look away (reflex) from what you are looking at to look at the light. If there are multiple light sources, the brighter one is the one with the most beam candela in your direction.

Car lights at night cause you to look away from the road and look at them. We condition ourselves to look away. High beams or improperly adjusted beams are brighter because of a higher beam candela in your direction.

When using a light to illuminate something, the brightness depends on the subjects reflectiveness. A higher reflective object will look brighter than a dull one.

When you turn a flashlight on, the impression of brightness depends on what you are trying to illuminate. Things get a little sticky from here. I like a beam with a decent size hot spot and ample spill light. Of course this varies with the distance to the object. The hot spot will illuminate my target, and the spill will lower the extreme contrast caused by the hot spot.

I find that when I am in the woods lights look dimmer, compared to when I am trying them out at home. The trees in the woods are not very reflective. I find that higher candela lights with a proper beam are brighter when trying to see distant objects.

Daylight is bright. Clear sky with sun is brighter. Sunshine in the woods is bright. Sunshine on the water is brighter.

Enough rambling for now.

Tom

Re: Just what do people mean by \"brightness\"?

The way people use the term, it's my impression that you need to tell by context what they mean. It is not consistently used across candlepowerforums, much less the outside world [wait, remind me, there still is an outside world, right?]

Re: Just what do people mean by \"brightness\"?

well, for indoor use i think of brightness as how far i have to hold a light away from the wall without blinding myself..

outdoors i think of brightness as throw + enough spill to avoid panning the light back'n'forth on trails..

Re: Just what do people mean by \"brightness\"?

Hello Doug,

I just asked my wife and she said to her brightness is intensity.

Tom

Re: Just what do people mean by \"brightness\"?

As I'm often told; women are always right.

Brightness is intensity - so it was, so it is and so it shall ever be (until woman changes her mind as is her want)

Al /ubbthreads/images/graemlins/grin.gif

Re: Just what do people mean by \"brightness\"?

wise words, Al /ubbthreads/images/graemlins/grin.gif
bernhard

Re: Just what do people mean by \"brightness\"?

they mean the visual perception along the black-to-white continuum.

Re: Just what do people mean by \"brightness\"?

i never even considered anyone would think anything other than all-over brightness (lumens) /ubbthreads/images/graemlins/confused.gif

Re: Just what do people mean by \"brightness\"?

Yep, intensity = brightness for me too. A large fluorescent lantern may fill a room with light but not be as "bright" as the beam from a small flashlight.

Re: Just what do people mean by \"brightness\"?

well put jayflash!

Re: Just what do people mean by \"brightness\"?

To me, brightness equates to throw. Want full, flooding illumination right around you? Flip the wall switch. /ubbthreads/images/graemlins/grin.gif

But seriously, when you need to see how relatively bright a flashlight is, you shine it at something and see how intensely it illuminates that thing back atcha. Such as when I finish a mod -- before adding the head with its optics/reflector installed, I turn it on to check for final function. And that wide, soft, true flood of light from the bare Luxeon will not tell me how bright it is compared to another identical mod (for some reason I seem to always be building identical mods in quantities greater than one) as they will illuminate things about the same.

It's when I try them with their collimating devices in place that I am able to see the real differences if there are any. Not just in "brightness", but in color, beam shape, artifacts, etc.

Your eyes need the Intensity to pick up on how really bright they are. Like Roy said, it's how we're built.

Re: Just what do people mean by \"brightness\"?

To me, brightness is a light that provides
a lot of contrast in dark and light areas
of the subject. Therefore some colored lights
may be bright in certain environmental
situations and not bright in others.
A light may be bright enough
to prevent me form stubing my toe in a dark
room, but a bright light will help me to see
details and accomplish different tasks.

-Rebus

Re: Just what do people mean by \"brightness\"?

A PR2 bulb driven by 2D is NOT bright by any standards I'm aware of. Neither is the could cathode flourescent bulb of a Trailfinder.

Both are damn usefull however!

4x123 driving a Carley or WA bulb, now that's BRIGHT!

I think it means intensity AND the effects of focus.

However usefull beats BRIGHT in most circumstances!

Re: Just what do people mean by \"brightness\"?

I think the answer for me is BOTH.

Intellectually I conceive of the brightness of a light source according to its overall output (lumens). But if I took the light from the 1000 lumen room bulb that's lighting this room and put it into a 5 degree beam flashlight, I would think it's too bright (candela) to use this computer, even though the amount of light is the same. My real-world relationship to the light is in terms of intensity.

So if someone asked me which of two flashlights is brighter, I would tell them the one that had higher lumens. But my actual usage of the lights would be dictated by the intensity of the beam.

Re: Just what do people mean by \"brightness\"?

Good discussion Doug. I agree: brightness is intensity.

The brightest "flashlight"? A laser pointer of course. /ubbthreads/images/graemlins/smile.gif Even has a warning label saying so.

Lumens is a good way to tell how much light you have to work with. How those lumens are distributed is also important. A beam shot with lumen data is good, a photometric distribution graph with lumen data is even better.

Getting an accurate lumen rating for a light is quite difficult. A well known brand recently found out that their integrating sphere was out of spec. Fortunately, it was under-valuing the numbers. /ubbthreads/images/graemlins/smile.gif But even if you use a certified lab (we do), you have to correctly set up the tests. Some lights loose quite a bit of their output in just a few seconds of run time.

Peter