Using Light Probes in Unity’s HDRP

Light probes are a great way to light up your scene without having to use a lot of expensive lights and excessive baking. Let’s take a look at the powerful light probe feature and how to use it.

In the Hierarchy, create a new Light>Light Probe Group.

You should see four light probes composing a cube in the scene view.

To make adjustments, click the Edit Light Probes button under Light Probe Group in the inspector.

Use the left mouse button to drag and select the probes you want to edit. With the top down orthographic view enabled, both top and bottom layers of probes are easily selected and repositioned.

Select the light probes that you want to duplicate, and then press the Duplicate Selected button.

The new probes can be dragged out into position.

Once you get a few out there, duplicating starts going quickly. This is a rough and fast layout. Ideally for the greatest effect, I want these floor probes to be on both sides of a color transition. This way as the player moves between different colored floor tiles, it will take on the floor reflection color in a more realistic fashion.

The side view is used to place different levels of probes throughout the scene. Here you can really see the intertwined web between the probes. Light probes fill the room with baked lighting information, so it’s important that they stay connected to communicate with each other.

To test this out I create two Sphere objects and a Spot Light. The Spot Light is set to Baked. These probes do not respond to dynamic lights, so having at least one baked light source in the scene is very important.

The first Sphere can stay as it is when created, and act as the player. It’s a naturally dynamic object with a neutral medium grey color that will move around the scene manually. I give the second sphere a material with an emissive color channel, and use a bright blue, cranking up the intensity in the HDR setting.

This sphere emitting blue light needs to be set to Static in the inspector for it to interact with the light probes. Pretend this sphere is a computer monitor, or television, or some light projecting object that is otherwise still, but you still want the light to interact with the appearance of the player. Light Probes are a great way to accomplish that.

While moving the player sphere around the scene view, light probes surrounding the player will appear, and show the light information that they have. The two black probes are outside of the range spotlight and not taking on any lighting information. The one lit probe is taking lighting info from the spotlight and projecting it on to the player. Also to note, the floor is also static now and receiving the baked light from the spot light.

You can see that the lower probe closest to the emissive object is taking on the most light.

As the player approaches the light emission, you can see the color lighten up and even take on some of the blue light.

Remember to let your light finish baking before inspecting the probes to see if they are working.

I took the spot light and put it high in the main room and expanded it’s range. I also gave it a warm temperature color.

Now the player takes on light from the warm spot light.

As the player leaves the scene, it takes light probe info from the warm baked light, while also being hit by a dynamic spot light as it crosses in front of the test tube.

I created a second cool spotlight and placed the two side by side. Here you can see the drastic color change as the player moves from cool, to dark, to warm light.

Here is another view with the light probe group visual turned off.

Thanks for reading and have fun making wonderful light!



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