photometric lights

mskin · April 3rd, 2008

Can anyone give me a pointer in using photometric light with max 9/mr? when i put them in the scene... its just darkness. altering the intensity of the lights doesn;'t seam to hlp much. im shooting for a linear light type of appearance. could be a units issue? i don't know.

Kyle · April 3rd, 2008

Try your camera exposure settings.

mattclinch · April 3rd, 2008

set your mr exposure to something standard for your shot.
use the photometric with intensity measured in candelas (cd) then check this page out
http://en.wikipedia.org/wiki/Candela
as a guide "A common candle emits roughly 1 cd. A 100 W incandescent lightbulb emits about 120 cd"
then re-adjust your exposure accordingly.

mskin · April 3rd, 2008

it is set to candela. the cd is set to 1500. still - not even a hint of light.

scene units set to inches... i noticed the lighting units were not set to si, but that had no effect as i can see.

SandmanNinja · April 3rd, 2008

Here are my notes from some tutorials I did recently - I'm at work, so don't have the time to 'clean' it up. hope this makes sense:

Quote:

Logarithmic Exposure Control Parameters
Rendering -> Environment (or press 8) -> Exposure Control -> Logarithmic Exposure Control
Brightness
Contrast
Mid Tones
Physical Scale

[x] Exterior Daylight - tick this if you're using MR Sun
If you don't, then the scene will be VERY over-exposed.
Allows you to continue working with a physically accurate scene

If you use an HDRI, be sure to tick [x] Process Background and Environment Maps

Logarithmic Exposure Control:
[x] Active
[x] Process Background and Environment Maps
[x] Exterior Daylight

If the render is dark, the Physical Scale is probably off.
Physical Scale is measured in candela units.
The typical scene ranges from 80000 to 120000 candela units
This value should be set to the value of the brightest light source (MR Sun, target light, etc)

If a light source emits one candela of luminous intensity uniformly across a solid angle of one steradian, its total luminous flux emitted into that angle is one lumen. Alternatively, an isotropic one-candela light source emits a total luminous flux of exactly 4 / pi lumens. The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source.

A standard North American 100 watt incandescent light bulb emits approximately 1700 lumens, while a 100 watt sodium vapor lamp emits around 15,000 lumens, about 9 times as much.

Physical Scale goes up to 200,000 units.
Photometric Lights are not affected by physical scale.
They work in a physically accurate scene.

Logarithmic Exposure Control:
[x] Active
[x] Process Background and Environment Maps
[x] Exterior Daylight
[ ] Colour Correction (manually set the white balance in your scene)
[ ] Desaturation Low Levels (in VERY LOW LIGHT scenes, it removes colour like in real life)
[ ] Affect Indirect Only (designed for scanline render engine)

Mid Tones: range from .01 to 20 Default is 1.0 Helps with contrast

April 3rd, 2008	#1 (permalink)
mskin Senior Member Join Date: Apr 2005 Location: nantucket Age: 34 Posts: 376 Name: herbert mellville	photometric lights Can anyone give me a pointer in using photometric light with max 9/mr? when i put them in the scene... its just darkness. altering the intensity of the lights doesn;'t seam to hlp much. im shooting for a linear light type of appearance. could be a units issue? i don't know.

April 3rd, 2008	#2 (permalink)
Kyle Member Join Date: Jan 2008 Location: London Posts: 80 Name: Kyle McBride	Re: photometric lights Try your camera exposure settings. __________________ *Pleasure in the job puts perfection in the work.*

April 3rd, 2008	#3 (permalink)
mattclinch Senior Member Join Date: Jun 2007 Location: W. London Age: 25 Posts: 209 Name: Matt Clinch	Re: photometric lights set your mr exposure to something standard for your shot. use the photometric with intensity measured in candelas (cd) then check this page out http://en.wikipedia.org/wiki/Candela as a guide "A common candle emits roughly 1 cd. A 100 W incandescent lightbulb emits about 120 cd" then re-adjust your exposure accordingly. __________________ Matt Clinch Arch Viz Artist @ Hayes Davidson http://www.hayesdavidson.com

April 3rd, 2008	#4 (permalink)
mskin Senior Member Join Date: Apr 2005 Location: nantucket Age: 34 Posts: 376 Name: herbert mellville	Re: photometric lights it is set to candela. the cd is set to 1500. still - not even a hint of light. scene units set to inches... i noticed the lighting units were not set to si, but that had no effect as i can see.

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