The Lights Under The Lake

Getting Started With The Lights Under The Lake

I've spent the last couple of years working with The Lights Under The Lake on a few different projects, and honestly it's one of those tools that looks simple on the surface but eats people who don't understand how it handles lighting at depth. The basics are straightforward — you place light sources, assign colors and intensities, and the engine does the rest. The problem is that the default behavior is not what most people expect. Here's what nobody seems to mention in the official docs: the light falloff under simulated water isn't linear. It follows a modified Beer-Lambert law, which means the deeper your light source sits in the hierarchy, the more aggressively it compresses. I learned this the hard way when a client complained that their underwater cave scene looked completely flat after we baked the final render. We had spent three days tuning individual light intensities, and every adjustment felt like whack-a-mole because the engine was silently clamping values at deeper nodes.

How To Get The Lights Under The Lake Working Correctly

First, make sure you're running version 3.2 or later. The earlier builds had a bug where ambient light would bleed into submerged scenes even when you disabled it explicitly. The patch fixed that, but you'll still see artifacts if you're upgrading from an old project file. Export your current scene settings before you install. The core workflow breaks down into three steps that most people mess up in order. You should set your water plane geometry first, then your light sources, then your camera rig. When you reverse that order the initial bake takes significantly longer and the results are worse because the engine recalculates refraction paths based on whatever geometry was present during the first pass. On a mid-range machine this can add about forty minutes to an otherwise fifteen-minute bake. For the water plane, use a subdivided plane with the shader preset called "caustic_diffuse." The other presets exist but they skip caustic calculations entirely, which makes everything look like it's lit from above a still glass surface rather than through actual water. Your lights should be positioned below the water surface but above the terrain floor. I usually recommend starting with three to five lights for a medium scene. More than that and you start seeing banding in the shadows unless you increase your shadowmap resolution to at least 2048.

Here's the thing most guides skip: you need to enable "depth_compensated_intensity" in the global render settings. Without it, lights that are physically closer together in 3D space will still render at the same brightness regardless of their simulated depth. This setting forces the engine to factor in vertical distance through the water column. My workaround for the cave scene I mentioned was to lower the default Beer-Lambert coefficient from 0.15 to 0.08 in the project preferences. That's a non-obvious fix because the slider is buried under Advanced > Subsurface > Water Optics, and the label doesn't tell you what it actually does.

Common Pitfalls And Where This Breaks

The Lights Under The Lake handles static scenes well. Dynamic elements — moving cameras, animated light sources, particles — introduce a different set of problems. I ran into a project last year where a moving camera caused the caustic patterns to tear across the terrain at frame boundaries. The issue only appeared on export, not in the viewport preview, which made debugging it take about six hours. The workaround was to disable real-time caustics and bake them as a texture sequence instead. It added about twenty minutes to the render pipeline but eliminated the tearing completely. Another limitation you should know about: the engine struggles with mixed lighting scenarios. If you're combining The Lights Under The Lake with a separate HDRI environment map, the two systems fight over the ambient term and you get double-exposed highlights around your light sources. I usually strip the HDRI down to just the sky color channel and let The Lights Under The Lake handle all illumination. It loses a bit of realism in the distant background but the underwater portions look significantly better. Memory usage is also worth watching. A scene with five lights at 2048 shadow resolution and caustics enabled will consume roughly 8 gigabytes of VRAM. If you're on a card with less than that, you'll get stuttering during playback even if the final bake succeeds. Downgrading shadow resolution to 1024 cuts memory roughly in half with minimal visible quality loss for most applications.

Where To Get It

You can download The Lights Under The Lake from the official distribution page at lightsofthelake.io/download. The standard license runs about ninety dollars and includes three years of updates. There's a free trial that limits you to scenes with two lights and no caustic support, which is fine for testing whether your workflow matches what the tool expects but not useful for any real production work. If you're working on something complex, I'd suggest buying the educational license if you qualify — it's half price and you get the same feature set. The validation process takes about two days though, so plan accordingly. One final note: don't try to use this for surface-level underwater shots where the water is only a meter or two deep. The depth-based falloff algorithms are tuned for scenes with meaningful vertical water columns. Shallow water looks wrong because the engine is calculating light loss over a distance that doesn't exist in your scene. For shallow environments, you're better off using a standard PBR water shader with a Fresnel node. The Lights Under The Lake is built for deep water simulation, and it shows when you push it outside that range.