How to use Light sources?

[Kranky]

Hello,

I tried to add a light source. Then I increased the height above the ground to about 100. Then I increased the source radius to 400 and chose a red color. After that I pulled the "Strenght" setting to about 300.

In the preview and also in the rendered image I cannot see any red light. Can anybody tell me, how I have to use light sources?

Jens

[cyphyr]

Hi Kranky
I re-created your scene and initially I could not see the light either. I then dropped the sun below the horizon and rendered again, still nothing. Then I started upping the light strength and got an acceptable result at about 300,000. Obviously the light source and sunlight use a different scale on their strength sliders. Maybe (just a guess) with a light source its measured in "lumens" in which case it would be a bit like holding a candle in broad daylight, no real effect until you really boost the power.
Richard

[Kranky]

Thanks for your test. I tought, 300 is a large value - but ok, I will try it with more 

[moodflow]

I also noticed this a few months ago.  You need HUGE numbers.

[Oshyan]

The luminosity numbers are I think measured in surface area, so the larger your light source radius, the higher the number will need to be for it to put out noticeable levels of light.

- Oshyan

[Matt]

The intensity value controls how much illumination power there is at distance of 1 metre. This intensity drops off according to the inverse square law, http://en.wikipedia.org/wiki/Inverse-square_law

The units are undefined, but they correspond to the same units used by the TG's sunlight. [EDIT: The units are defined with respect to the pixel intensity in the final image, as they are in TG's sunlight.]

The difference between Sunlight and Light Source is that in Light Source these values only apply at a distance of 1 metre, so much larger values are needed to illuminate well at larger distances.

Source radius only has an effect on the amount of illumination very close to the light source. It prevents the intensity from getting any brighter within the radius specified, and it also affects intensity at some small distance outside the radius.

Matt