# How to scale a light's size , and strength proportionally with the rest of the scene in Cycles?

I have a question regarding the scaling of lights alongside the scaling of a scene in Blender.

Say I have a scene consisting of a plane acting as a surface, and a simple white UV Sphere. Both are at their default size

I have an Area lamp shining directly perpendicular to the top of the UV sphere. The Area Lamp is at a distance of 6 units on the Z-axis, while the UV is at 0 .

I want to scale the entire scene down by a sixth of its original size. I can scale both the plane and sphere by 1/6 to reduce them to a sixth of their size

However, when I do the same to the area light, and reduce its strength and size by sixth in the material editor, it simply does not light the scene the same way as prior to scaling

So with that, comes my question. How do I scale everything in the scene , lights included , while also maintaining the same distance between mesh and lights, proportionally so that they look the exact same as before in the render, with only the scale values affected?

As you can see in following images,first image is how it looks un-scaled. This is how the scene should LOOK

In the second image, Mesh,plane are scaled by a sixth, light strength size scaled by sixth. Still does not look like first image at all

• Hello :). You need to scale the light strength according to the inverse square law. It's not linear. – Jachym Michal Jun 1 '20 at 18:46
• @JachymMichal so if it follows the inverse square law, what values should I plug in into the area lamp , in my case to match the first picture? – Hash Jun 1 '20 at 18:47
• Use the link, it's a calculator :). I'll post a full answer if I find the time. – Jachym Michal Jun 1 '20 at 18:53
• @JachymMichal I don't see a calculator or link? – Hash Jun 1 '20 at 18:55
• @brockmann I'm sorry, I don't get you. Ate you asking me to use the calculator app? If so, what values do I plug in? – Hash Jun 1 '20 at 19:01

You need to scale the light intensity according to the inverse square law. [Calculator]

• When dividing scene size by 6, divide light power by 36.
• When dividing scene size by 10, divide light power by 100

Important note:
Point and Spot lights don't change their Size when scaled with the scene. You need to change their Size manually in the Lights panel. Area lights scale properly with the rest of the scene.

Example:
Scene scale divided by 6. Point light Size also divided by 6. Point light power divided by 36.

• Yes, but would I have the need to change the distance of the lamp to the mesh? Since the mesh and scene have gotten smaller, they are farther away from the lamp, even if the lamp is scaled down right? So I would need to move the light? Or would the changing of the lamp size and strength negate the need to move lamp closer to mesh? – Hash Jun 1 '20 at 21:11
• Yes, you need to change the lamp distance. Just select the whole scene and scale it to 1/6. This way your camera and shadows will match perfectly :). – Jachym Michal Jun 1 '20 at 21:14
• Whole scene including lights? But if I scale down the light in viewport , and then do the same in the property/material editor thing, would I not have scaled it down twice, causing an issue? – Hash Jun 1 '20 at 21:16
• Hey :). Point and spot lights don't change their Size when you're scaling the scene. Only Area lights do. I updated the answer :). – Jachym Michal Jun 1 '20 at 22:04
• so if I change size of area light in viewport, it changes in the editor and vice versa? – Hash Jun 1 '20 at 22:06