Let’s say I have an empty scene with a single point lamp, Size 1m and Strength 100. If I just switch to Eevee, the light will look very different. How do I change the light properties so it looks the same in Eevee (same amount of light, same area lit, same shadow softness)?
Eevee lights have an object level Power that’s outside of the shading nodes. In fact I don’t think you can have nodes on a light in Eevee. The default value for a point light is 10W, and this is effectively 10x stronger than the same light in Cycles, so to make Cycles look like Eevee currently you have to enable nodes in Cycles for the light and increase the Emission node strength from 100 to 1000. To go the other way you can just set the Eevee lamp Power to 1W to match the default light strength from Cycles.
The plan is to normalize the settings between the renderers, adding the object level power to Cycles just as Eevee has so that nodes won’t be necessary in either, and there’s a patch waiting in the wings to start doing this, but it’s tricky to automatically update existing scenes without potentially getting things wrong in some cases. See: