Lumens

alaltaccalaltacc Posts: 9
edited January 14 in New Users

Hello!

   I know lighting is a complex theme and I'm not hoping to learn how to use it correctly in the forums. I'm watching a lot of tutorials to get a better grasp of it. For the HDRI part I'm already going somewhere, but when it comes to create my own lighting from the light types available inside DAZ it's a different story.

   Anyway, my question is very specific: a real-world 100W incandescent (or, being more up-to-date, 20W LED) lamp gives around 1600 lumens of light. So, the newbie here thought that, creating an enclosed space of about 12 square meters and placing a light (I've tried both point and spot lights) of around 1600 lumens in the ceiling, the place would be as lit as my bedroom would with a 100W incandescent lamp. The reality was a very dark, almost impossible to see environment, where the render would get almost nothing.

   Even after putting four 100,000 lumens spots, one in each corner looking to the opposite corner, and opening up their emission radius, I still had very dark parts and lots of shadows. That would be 400.000 lumens in the real world, or about 250 100W incandescent lamps, enough to bring down a small powerplant. cheeky I've tried point lights also, with the same results.

   What am I doing wrong? Is my correlation between real-world lumens and Daz-lumens off?

   Thanks!

Post edited by alaltacc on

Comments

  • FishtalesFishtales Posts: 5,608

    You have to use Tone Mapping too. The camera doesn't 'see' like your eyes so you have to use Tone Mapping settings to compensate. If you walk into a room with a camera and just take a picture it wont be the same as you see with your eyes so you have to set the camera to 'see' the room as your eyes do.

  • cridgitcridgit Posts: 1,534

    I did some test renders of a head with spotlight/ppint light at different distances and lumens, and put this together in a one page reference (rows x columns) as a guide when I need to guess the right numbers. When using spotos I never use anything less than 25,000 and sometimes go up to 500,000.

  • FishtalesFishtales Posts: 5,608
    edited January 15

    I have closeup pictures using one spot at 1500 lumen and the lighting is fine.

    Post edited by Fishtales on
  • cgidesigncgidesign Posts: 113
    edited January 15

    As Fishtale said:

    Room 10 x 10 m / 4 m height.

    Single point light with 2000 Lumen. Exposure Value in this case = 5.

    tone-mapping.png
    1471 x 875 - 802K
    Post edited by cgidesign on
  • PerttiAPerttiA Posts: 3,815

    If you set "cm^2 Factor" in tone mapping to 10, the lumen values can be set close to their real world values.

  • FishtalesFishtales Posts: 5,608

    PerttiA said:

    If you set "cm^2 Factor" in tone mapping to 10, the lumen values can be set close to their real world values.

    Or just set the Luminance Units to cd/cm^2 in the Emission settings. 

  • cgidesigncgidesign Posts: 113
    edited January 15

    All the values of:

    • Shutter Speed
    • F/Stop
    • Film ISO
    • cm^2 Factor

    do change the Exposure Value. The Exposure Value is the result of a combination of the other values. Its like in real world photography. E.g. if you increase the Film ISO and use a faster Shutter Speed accordingly you get the same Exposure Value. But in real world photography the shutter speed and ISO etc. have additional effects which are not really relevant in Iray. So, whatever value you change, in the end you get your desired Exposure Value.

    Regarding the real world values mentioned. I am not sure if I would call it like that. The real world values are already set by using a build in light because they use a light fall off of cm^2 internally which is similar to real world behaviour. If you then use e.g. 1500 Lumen you have roughly a real world inhouse light bulb scenario. The exposure value just tells Iray how sensitive the camera's eye is. The lower the value the more sensitive to light the eye is = the brighter the render gets.

    Post edited by cgidesign on
  • PerttiAPerttiA Posts: 3,815

    cgidesign said:

    Regarding the real world values mentioned. I am not sure if I would call it like that. The real world values are already set by using a build in light because they use a light fall off of cm^2 internally which is similar to real world behaviour. If you then use e.g. 1500 Lumen you have roughly a real world inhouse light bulb scenario. The exposure value just tells Iray how sensitive the camera's eye is. The lower the value the more sensitive to light the eye is = the brighter the render gets.

    I think one of the problems is the reference to cameras... "If you take a picture inside it looks different than what you see with your eyes..." - Don't care how it looks through a camera, I want the render to look as I see it with my eyes 

  • FishtalesFishtales Posts: 5,608

    PerttiA said:

    cgidesign said:

    Regarding the real world values mentioned. I am not sure if I would call it like that. The real world values are already set by using a build in light because they use a light fall off of cm^2 internally which is similar to real world behaviour. If you then use e.g. 1500 Lumen you have roughly a real world inhouse light bulb scenario. The exposure value just tells Iray how sensitive the camera's eye is. The lower the value the more sensitive to light the eye is = the brighter the render gets.

    I think one of the problems is the reference to cameras... "If you take a picture inside it looks different than what you see with your eyes..." - Don't care how it looks through a camera, I want the render to look as I see it with my eyes 

    Your brain is your Tone Mapping software that is inside a camera and in the Studio software. Your eyes are the lenses that allow the light in changing shape and diameter of the pupil to change the amount and zoom, the same as the F/stop and zoom on a lens and in the Tone Mapping software. Original cameras, film and lenses were all based on what was known about the human eye and brain. Ignoring that fact diminishes your understanding of how your eyes and a camera work.

  • PerttiAPerttiA Posts: 3,815

    Fishtales said:

    PerttiA said:

    I think one of the problems is the reference to cameras... "If you take a picture inside it looks different than what you see with your eyes..." - Don't care how it looks through a camera, I want the render to look as I see it with my eyes 

    Your brain is your Tone Mapping software that is inside a camera and in the Studio software. Your eyes are the lenses that allow the light in changing shape and diameter of the pupil to change the amount and zoom, the same as the F/stop and zoom on a lens and in the Tone Mapping software. Original cameras, film and lenses were all based on what was known about the human eye and brain. Ignoring that fact diminishes your understanding of how your eyes and a camera work.

    That would be a valid argument if talking about real world photograph, but when talking about an image on the viewport that's already an image through a virtual camera vs the same image when rendered, there is no excuse for the former to be properly lighted and the latter turn out completely dark.

  • The Viewport mode, depending on which you are suing, doesn't cast shadows so you may have the working view lit by external sources thata re blocked in a full render. You may also have turned Preview Lights off, so the scene is lit by a pseudo headlamp and not by an approximation to the real lighting.

  • PerttiAPerttiA Posts: 3,815

    Richard Haseltine said:

    The Viewport mode, depending on which you are suing, doesn't cast shadows so you may have the working view lit by external sources thata re blocked in a full render. You may also have turned Preview Lights off, so the scene is lit by a pseudo headlamp and not by an approximation to the real lighting.

    When the Preview Lights are on and the scene is lit with light sources having lumen values that would be enough to illuminate the scene to resemble "normal Office room lighting"

  • PerttiA said:

    Richard Haseltine said:

    The Viewport mode, depending on which you are suing, doesn't cast shadows so you may have the working view lit by external sources thata re blocked in a full render. You may also have turned Preview Lights off, so the scene is lit by a pseudo headlamp and not by an approximation to the real lighting.

    When the Preview Lights are on and the scene is lit with light sources having lumen values that would be enough to illuminate the scene to resemble "normal Office room lighting"

    That would depend on the lights being previewed - though as I said, the preview doesn't reflect shadow casting which may have a significant effect. or are you confusing Preview Lights on (the default) with turning Preview Lights off and geting a pseudo-headlamp instead?

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