Totally misunderatanding Linear and NoDecay options in Light Settings

[mikekoenig]

There is NoDecay options in Rectangle Light saying there is NO DECAY for this lightsource
nice... I got it and using it to add additional light to big scenes.

But using Omni and Spot Light i have following options:

Decay type:

Linear
Inverse
Inverse Squared

Documentations says - the first one gives "NO DECAY" - wtf?
It decays!!! Really slow but rendering big scenes - you can see it perfectly - but it decays...

Furthermore - manuals tells Inverse mode decays light brightness in LINEAR way wtf2??? What stays behind first option naming in this case?
Of course - i can get practical using difference using it myself - the first and second options are BOTH LINEAR for me - but with some coefficient.

But i'm teaching my students and walking around this particular options very careful trying to keep silence about this modes naming...
The same with SpotLight penumbra Angle Decay... - there are two methods - Linear and Cubic... I cannot clearly recognize this naming comparing render results.

Someone can make me clear in this issue?
Better - with some formulas or diagrams like

[andybot_cg]

Yes, it does sound like you are misunderstanding. The light options work just as expected for me, it may be you are confused by the explanations. Here is a demo of the three types of falloff.
There is no decay for the linear light, you may just be seeing a GI or sampling effect.
You can see in the samples the difference between inverse and inverse square falloff

[fpedrogo]

Hi Guys
Decay - allows you to choose the behavior of the light intensity from the distance of the light source. Normally the light intensity is inversely proportional to the square of the distance from the light (surfaces that are farther from the light are darker than surfaces which are closer to the light). The possible values are:

Linear - when this option is on the intensity will not decay with distance.

Inverse - light intensity inversely proportional to the distance from the light.

Inverse Square - light intensity inversely proportional to the square of the distance from the light. This is the normal behavior of light.

The rectangular light only have No Decay option. So when this option is disable we are using inverse square decay. When the option is enable we are using linear decay. Inverse square is the most physically correct effect.

Best

[mikekoenig]

Thanks all of you for answers. I'm really understand physics of each option. The only one thing is discouraged me - it just naming...

Linear - will not decay... Hm.... I thought Linear function is not the same as Constant...
Inverse - light intensity inversely proportional to the distance from the light - Isn't THIS CALLED LINEAR in Math?

and finally

The rectangular light only have No Decay option - When the option is enable we are using linear decay.... Shooting in the head - Third meaning... IMHO - No Decay = 0. So light will keep it's insensitivity FOREVER (like ambient light)... Not linear decay as it works ....

Again - it's just my considerations about naming... I'm absolutely know the visual difference and then to use each option in a