The default setting for lights is Falloff = Constant. This causes a lot of hideous, blown-out renders if you forget to check it. So, yes, most of my students forget to check it.
Can we please change this to the more real-world setting of ‘Fallof = Inverse Squared?’ For example, all lights ever made, fire, and the sun all work this way. 
Yeah… I can see this biting users either way - with inverse square falloff, many lights, depending on the scale of the scene and units, may seem to do nothing at all - Constant has the advantage, even if it is ‘wrong’ of being scale independent and always showing a ‘useful’ result.
@BrianJ - any thoughts on this?
-Pascal
I totally understand that it might be easier initially.
However, I always stress that we build models to correct, real-world units. It seems odd that a model can be the right size / scale / units but the lighting doesn’t respect that.
Not to mention, if you move the light closer or farther away, absolutely nothing happens. Lighting size and distance are important variables to dial in your illumination.
I mean, sure…but without the light intensity units also being “real-world” by default, and the render gamma being set right by default, and possibly more settings than that, this alone isn’t going to do that much…
Of course it’s only “odd” in the current timeframe of GPU path-tracers for lights to not behave realistically by default, and I never actually use those 80s-era simplified fake “light objects” anymore, it’s HDRIs and brute-force models of actual lamps.
Another good point.
I have found that the HDRIs are great for ambient / environmental lighting, even if they definitely are on the advanced side for beginners. We still need a good old-fashioned adjustable rectangular light to kick out those sexy product highlights.
In our class, you’ll see students doing really well moving the top-key-rectangular light closer and further away until they get those highlights right where they want them.
The occasional issue with HDRI-only lighting is that you don’t see it in the viewport. If there was one HDRI map that made every model look awesome, I’d be using it! 
I will do some more research on this and get back to you. QUESTION > I have noticed that the lighting is sometimes NOT changing l when I use inverse-square-falloff and move it around. If you could clarify what’s up, that would be super useful.
An aside, but
! _EditLightByHighlight
There is a Line option as well to just place a reference.
-Pascal
Hi Dave - If you are in a Raytraced viewport, see if switching to wires and then back again kicks off the light change. There is a bug there someplace, I think but I have not been able to repeat it on demand.
-Pascal
Hey @pascal
I am talking about the formal rendering, the the rendered viewport.
I’ll run some tests ASAP and post here.
Hi Dave, I think the rendered viewport may be quite restricted in how it can display changes - a limited number of ‘steps’, so the change you make may not be large enough to change what is whown on screen.
You can see the banding pretty clearly here
-Pascal
