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Thread: Ambient light vs Incident Light

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    Ambient light vs Incident Light

    Is there a difference? Is a flash incident light?

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    Have a guess :)
    Good question -- looking forward to reading the answers!

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    Re: Ambient light vs Incident Light

    Unlike Colin who for whatever reason decided not to answer your question, I'm not an expert on lighting terminology. So, I'm also interested in the proper answer to your question.

    I have only seen the term "incident light" used in the context of "reflected light," not "ambient light." As an example, an incident light meter measures the light falling onto an object. A reflected light meter, which is the kind that is included in camera bodies, measures the light being reflected from an object. If I'm right about all of that, all ambient light is both incident and reflected light. Similarly, all light generated by a flash unit is also incident and reflected. Indeed, all light is both incident (because it falls on a subject) and reflected (because it is reflected by a subject).

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    Re: Ambient light vs Incident Light

    Here's my two bob's worth :

    The word ambient means "of the surrounding area" and is used in terms like ambient temperature and ambient noise (sound). We had a thread recently where the term ambient light was used to distinguish between light in the general surroundings and light specifically produced by a flash.

    Incident light on the other hand refers to light striking a surface. This term is used to distinguish between light falling upon a surface and that reflected off it.

    So if we are photographing an object, then the reflected light off that surface is the light that enters our camera (although there may be some direct light entering the camera as well). The incident light on that object's surface could be from ambient light or a flash.

    Make sense ?

    Dave

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    Re: Ambient light vs Incident Light

    Ambient light is the light from all sources present in a given situation whereas incident light is the light illuminating or falling onto a given object. A flash contributes to ambient light,however the main intent is to increase the incident light. Ambient lighting would be either using the natural light present in a situation or indirect lighting with some sort of artificial light(s) to increase the overall amount of light present.

    The incident light reflected off an object is what a spot meter measures; the ambient light would be what you measure if you get a general readings of the area the object is in.

    And I will happily stand corrected if someone better at optics and physics can chime in on this.

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    Re: Ambient light vs Incident Light

    Dave you do make sense. On a very sunny day in Queensland the ambient light may be very high but the incident light falling on the face of someone covered by a large sunhat (dangling corks etc) will be much lower. Of course if you use a mirror to reflect the sun directly into their eyes the incident light on the eyes may be much stronger than the overall ambient light.
    Last edited by pnodrog; 25th November 2012 at 01:18 AM.

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by tbob View Post
    The incident light reflected off an object
    Based on my understanding, that is an oxymoron. Incident light is the light falling onto an object. Reflected light is the light reflected from an object.

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by pnodrog View Post
    Dave you do make sense. On a very sunny day in Queensland the ambient light may be very high but the incident light falling on the face of of someone covered by a large sunhat (dangling corks etc) will be much lower. Of course if you use a mirror to reflect the sun directly into their eyes the incident light on the eyes may be stronger than the overall ambient light.
    Yes Paul, the question of incident light also comes into arguments against daylight saving (which we dont have here). The opponents to daylight saving, particularly those with dangling cork hats, get worried about things like fading curtains etc

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by Mike Buckley View Post
    Based on my understanding, that is an oxymoron. Incident light is the light falling onto an object. Reflected light is the light reflected from an object.
    True. Hope I didn't confuse the issue.

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by tbob View Post
    True. Hope I didn't confuse the issue.
    No, I doubt that you confused the issue because until the light is finally absorbed the reflected light from one surface will become part of the incident light on another surface. As a kid I loved those Barber shop mirrors - they were confusing.

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by Mike Buckley View Post
    all ambient light is both incident and reflected light. Similarly, all light generated by a flash unit is also incident and reflected. Indeed, all light is both incident (because it falls on a subject) and reflected (because it is reflected by a subject).
    Now that I have thought that through, I realize that I'm wrong and am a bit disappointed that nobody has corrected me. If the ambient light or light generated by a flash unit is shining directly toward the camera, it is only incident light, as it is is not falling on an object in the scene and is not being reflected off anything.

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by Mike Buckley View Post
    Unlike Colin who for whatever reason decided not to answer your question
    Just had a feeling about this one

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by Colin Southern View Post
    Just had a feeling about this one
    And I just had a feeling that you had a feeling.

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by Colin Southern View Post
    Just had a feeling about this one
    Yes it could get ugly !

    Dave

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by dje View Post
    Yes it could get ugly !

    Dave
    and why biologists should avoid talking physics

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    Re: Ambient light vs Incident Light

    I am not going to get into this discussion, but I found it interesting that less than 2.5 hours after the original question was asked, that this thread shows up #5 on a Google search for "Ambient vs Incident Light".

    Crazy how fast information can travel now a days whether it's correct or misinformed, huh?

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by Andrew76 View Post
    I found it interesting that less than 2.5 hours after the original question was asked, that this thread shows up #5 on a Google search for "Ambient vs Incident Light"
    That's downright scary.

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    Re: Ambient light vs Incident Light

    Quote Originally Posted by Mike Buckley View Post
    That's downright scary.
    It may happen more frequently than we would guess. A while back I posted an image of a tombstone statue and when I tried to identify it on the web, the only reference to that particular statue I could find was my entry here at CiC, complete with the image I had posted!

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    Re: Ambient light vs Incident Light

    I know when I Google my name, first then last - Cambridge in Colour pops up number 2, right behind Face Book. Not that I care - it's the age that I live in, and the age that I'm raising my children in, so I will deal with it, and it truly doesn't bother me, but It's crazy since my last name is quite unique, and I'm the only 'Andrew' with that last name in the world, and the only place it occurs on this site is in my Project 52 thread - not even in my personal profile, and yet Google picks up on that. Crazy.

    Anyhow - how about that Incident Flash Light??

  20. #20
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    Re: Ambient light vs Incident Light

    Ooops, did I give it away?

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