Why is my spot light not working?

I'm trying to follow along with a blender beginner tutorial, and I'm having trouble with spot lights. All other lights seem to work fine but I can't get spot lights to work.

Light isn't really doing anything to the scene, I can delete it and it'll look the same.

You can find the blend file here - https://drive.google.com/open?id=0ByReRoh-9WDQNVRoLXAzRjVCOWM

• Crank up Strength to something like 5000 and Size to 10 or more. Commented Apr 29, 2017 at 0:27
• You need to increase the strength of the light source, from the screenshot I can see that the scale of the objects are not realistic, scaling the lamp is not changing the amount of the energy that it emits. Commented Apr 29, 2017 at 0:28
• Ohh I see. I messed with the strength to no avail, but I just hadn't used a high enough value. If someone would care to make an answer I could mark it as solved. Thanks! Commented Apr 29, 2017 at 0:31
• Ok, I'll make one in a second with explanation why this happens. Commented Apr 29, 2017 at 0:35

There are two solution to this problem and they came from a scale of a scene.

After switching units to metrics (or imperial) you can see that your plate has radius over 3m, Lamp is 13m high above and size of 9cm.

1. You can crank up a light source Strength to something really high like 5000 and change Size accordingly.

2. You can scale down objects similarly to real world scales and make it a little bit physically correct. Then light won't need enormous values.

• – user1853
Commented Apr 29, 2017 at 0:48
• @cegaton Great find! I've stumble upon it a while ago but couldn't find it now to point answer to real calculations. Commented Apr 29, 2017 at 0:51
• In cycles the values of the lights are based on the real world. For a scene like the one in the question, in which the donut is the size of a car, and the cup is as tall as a building, you need quite a bright spot light.
– user1853
Commented Apr 29, 2017 at 0:53
• @cegaton This is literally what is told in my answer. Just putted in other words or maybe not in such direct manner. Commented Apr 29, 2017 at 1:23

To add to that, you can click on "Show Cone" option. This way, when you move a spot around, you can see the cone projection on the object and the background falloff estimate.

• While this will help to visualize what the lamp is about to lit it won't show how bright it will be in those areas. Commented Apr 29, 2017 at 11:13
• @MrZak - That's why I said "To add to that" and that it will give an estimate. Did not understand your point? Commented Apr 30, 2017 at 8:46

So, this is a problem I have been experiencing for just under a year and have just figured out what it has been for me. I found it by looking at cgslav's post.

For me, it was a simple matter of the location being at a negative value.

I found this by pressing N to open the side menu and saw that my light was 120 metres below my object, even though it didn't look that way in the viewport.

It seems that when you move the light around in blender on multiple axis it gives unpredictable values for metric based location... which makes sense since it's a program based on scale and not metres :/