OSL Painting: How to Paint Object Source Lighting on Miniatures

Hey again, friends. There's a moment that happens with almost every miniature painter. You're scrolling through Instagram or Reddit, and you see a model where a glowing sword is casting blue light across the marine's chest plate. The light fades as it reaches the shoulder. The opposite side of the model stays dark. And your brain, for just a second, thinks the light is real. That's object source lighting done right. And it's one of the most powerful effects you can put on a miniature.

It's also one of the most commonly botched effects in the hobby. I've painted OSL that looked incredible, and I've painted OSL that looked like I dunked the model in fluorescent paint and hoped for the best. The difference between great OSL and terrible OSL isn't talent or brush control. It's understanding how light actually works and having the restraint to apply that understanding with a lighter hand than your instincts want. Let me walk you through what I've learned.

What OSL Actually Is

Object source lighting means painting a light source onto a model and then painting the effect of that light on the surrounding surfaces. The "object" is the light source. A torch, a glowing weapon, a plasma coil, a magical spell effect, lava beneath the model's feet, a lantern on a belt. Anything that would logically emit light in the scene you're creating.

The "lighting" part is everything else. It's the color cast on nearby armor plates. The warm glow on a face lit by firelight. The way a green plasma gun throws sickly light across a gauntlet. You're painting something that doesn't physically exist (light) using opaque paint on a solid surface. It's an illusion, and like all good illusions, it only works when the viewer's brain fills in the gaps correctly.

That last point is important. You're not actually illuminating anything. You're giving the viewer enough visual cues that their brain interprets flat paint as directional light. This means your job isn't to paint every surface exactly as it would appear in a photograph. It's to paint the key signals. Brightness near the source. Falloff with distance. Color on surfaces that face the light. Darkness on surfaces that don't. Get those signals right and the illusion works, even if the physics aren't perfect.

Choosing a Light Source Color

The first decision is what color your light source will be. This isn't just aesthetic. It determines every other color choice in the OSL effect.

Cool colors (blue, green, teal) are the easiest for beginners because they create strong contrast against warm-colored models. A blue plasma glow on a red or brown model pops instantly. Cool light also reads as "magical" or "technological" to most viewers, which makes sense in sci-fi and fantasy settings.

Warm colors (orange, yellow, red) are trickier because they can blend into warm armor tones and lose their impact. A torch casting orange light onto already-orange armor barely registers. Warm light works best when the surrounding model is cool-toned or neutral. A campfire scene with dark blue-grey cloaks lit by warm firelight? Beautiful. A Khorne berzerker with red armor lit by a red weapon? Barely visible.

White/bright neutral light is the hardest to pull off convincingly. White light should theoretically just brighten surfaces without changing their hue, but on a painted miniature that reads as "bad highlights" rather than lighting. Tint your white light toward warm (slightly yellow) or cool (slightly blue) to give the viewer's brain a color cue to interpret.

General rule of thumb: your light source color should contrast with the dominant color of the model. Contrast is what makes OSL visible and dramatic. If the light blends into the model's palette, nobody will see it.

Where Light Falls (and Where It Doesn't)

This is the most critical part of OSL and where most people go wrong. Light travels in straight lines from its source. It hits surfaces that face the source. It does not hit surfaces that face away from the source. It does not wrap around corners. It does not illuminate the back side of the model if the light is on the front.

Before you put brush to model, hold a finger or a pen next to the light source position on your model and think about which surfaces would actually be lit. A glowing sword held in the right hand would cast light across the right side of the chest, the inner face of the right arm, the front of the right leg, and maybe the underside of the chin if the sword is low. It would NOT light the left shoulder, the back of the model, or the top of the head (unless the sword is held overhead).

The surfaces in shadow need to stay in shadow. This is where restraint comes in. It's tempting to put the glow color everywhere because it looks cool. Resist that. The contrast between lit and unlit surfaces is what sells the illusion. If everything glows, nothing glows. The dark areas are just as important as the bright ones.

Edges and raised details that face the light should catch it. Recesses that face the light should also be lit (this is the opposite of normal shading, which is why OSL can feel weird to paint). Flat surfaces facing the light should have a smooth gradient of illumination. Think about it from the light's perspective. What can the light "see"? Paint those surfaces. Everything it can't see stays as your normal paint job.

Falloff: The Secret to Convincing OSL

Falloff is the gradual dimming of light as it travels away from its source. Light doesn't maintain full brightness forever. It gets weaker with distance. On a miniature, this means the surfaces closest to the light source should be the brightest, and the effect should fade as you move away.

The most common OSL mistake is painting the entire affected area at the same intensity. Uniform brightness looks like you colored the model with a marker, not like a light source is illuminating it. The gradient from bright to dim is what makes the viewer's brain register it as light rather than paint.

In practical terms, the surface right next to the light source (within a centimeter or so on a 28mm model) should have a strong, opaque application of your glow color. A few centimeters away, the color should be transparent and barely tinted. Beyond that, nothing. The transition between "lit" and "unlit" should be gradual and smooth, not a hard line.

This is where glazing becomes your primary technique. Building up the glow gradually with thin, transparent layers gives you total control over the falloff. The area closest to the source gets five or six glazes. The area a bit further gets three. The area at the edge of the effect gets one. The transition happens naturally because each additional glaze adds density to the closer areas without touching the further ones.

The Painting Process

Step one: finish your model normally. Paint the entire miniature as if the OSL doesn't exist. Complete basecoats, shading, highlighting. Everything. This is your foundation, and any OSL you add goes on top of the finished paint job. Don't try to paint OSL and regular shading simultaneously. Your brain will melt.

Step two: plan the effect. Decide where the light source is, what color it is, which surfaces it hits, and roughly how far the effect extends. You can sketch this out mentally or mark the affected areas with small dots of blu-tack so you have a visual reference.

Step three: paint the light source itself. The object that's glowing needs to be bright. Very bright. If it's a sword, paint the blade white or near-white, then glaze your glow color over it. The center should be almost pure white (the hottest, brightest point) with the color intensifying toward the edges. A glowing green sword should be white in the middle, intense green at the edges, and darker green where the blade meets the hilt. The source needs to be the brightest point on the entire model, or the illusion falls apart.

Step four: glaze the nearest surfaces. Mix your glow color very thin. Like, "is there even paint on my brush?" thin. Apply it to the surfaces closest to the light source. Let each layer dry before adding the next. Build it up gradually. Three to five thin glazes on the brightest areas, tapering to one or two at the edges of the effect.

Step five: re-establish the highlights. Once you've built up your glow, go back and paint very thin edge highlights on the details within the lit area using a lighter version of your glow color (glow color mixed with white). This re-establishes the surface detail that the glazes softened and makes the lit area look like actual illuminated surfaces rather than a flat color overlay.

Step six: evaluate from arm's length. OSL is one of those effects that looks completely different up close versus at viewing distance. Hold the model at arm's length (tabletop distance) and squint. Does the glow read as light? Is the brightest point clearly the source? Does the effect fade with distance? If yes, you're done. If something looks off, adjust with additional glazes or by darkening areas that shouldn't be as bright.

Fluorescent Paints for Extra Punch

Fluorescent paints are a cheat code for OSL. Fluorescent pigments absorb UV light and re-emit it as visible light, making them appear unnaturally bright. On a miniature, fluorescent paint in the brightest part of your glow creates an intensity that regular paint simply can't match. It looks like it's actually glowing, especially under daylight or UV-enhanced lighting.

Use fluorescent paint sparingly and only in the area immediately around and on the light source. The rest of the OSL effect should be done with regular paint. If you use fluorescent everywhere, the whole effect loses its impact. Think of the fluorescent as the "hot center" and regular paint as the "fading glow."

Fluorescent paints are available from several hobby brands. Vallejo makes a fluorescent range. Scale75 has excellent fluorescents. Even cheap craft-store fluorescent acrylics work fine for this purpose since you're using them in small quantities and they'll be sealed under varnish.

Common Mistakes

Too much glow, everywhere. The number one OSL killer. If the glow color appears on every surface of the model, it reads as a color shift in the paint scheme rather than a lighting effect. Be ruthless about limiting the effect to surfaces that face the light source and are within a reasonable distance.

No falloff. A uniform layer of glow color at the same intensity from the source to the furthest affected surface looks flat and painted rather than lit. The gradient from bright to dim is not optional. It's what makes OSL work.

The light source isn't bright enough. If the object that's supposed to be glowing isn't dramatically brighter than the surrounding surfaces, there's no visual anchor for the lighting effect. The source should be the single brightest point on the model. Paint it lighter than you think you need to.

Wrong color temperature mixing. A warm orange glow on warm orange armor disappears. A cool blue glow on an already-blue model is barely visible. Your glow color needs contrast against the model's palette. If it doesn't contrast, either change the glow color or accept that the effect will be subtle.

Lighting surfaces that face away from the source. Light doesn't bend around corners. If a surface faces away from the light, it stays in shadow regardless of how close it is. Getting this wrong instantly breaks the illusion because the viewer's brain knows (even subconsciously) that light doesn't work that way.

Attempting OSL before the model is finished. Paint the model normally first. Then add OSL. If you try to do both simultaneously, you'll end up second-guessing every shadow and highlight, and the whole model will suffer. OSL is a final layer applied on top of a complete paint job.

When OSL Adds to a Model vs. When It Distracts

Let's be honest. Not every model benefits from OSL. The effect works best when it serves the narrative of the piece. A wizard casting a spell, a plasma gun charging, a torch in a dungeon, lava beneath a hero's feet. These are scenarios where a visible light source makes sense and OSL enhances the storytelling.

Where it can go wrong is when the OSL competes with the focal point of the model. If you have a beautifully painted face and then slap a massive green glow across the chest that draws the eye away from the face, the OSL is actually hurting the model. The glow becomes the focal point instead of the part you spent the most time on.

A good test: is the light source an important part of the model's story? If yes, OSL supports it. If no, maybe the model is better without it. A Space Marine holding a tactical bolter doesn't need OSL. That same marine holding a glowing power sword in a dramatic pose absolutely does.

Also consider the context. A model painted for display and photography can afford subtle, complex OSL that rewards close inspection. A model for tabletop gaming needs OSL that reads from three feet away. Gaming OSL should be bolder, higher contrast, and less nuanced than display OSL. Different contexts call for different approaches.

OSL is one of those techniques that intimidates people more than it should. The physics of light are predictable. Bright near the source. Fading with distance. Only on surfaces that face the light. If you can hold those three rules in your head and apply thin glazes with patience, you can paint convincing OSL. The trick is knowing when to stop. Less is almost always more. A subtle glow that makes the viewer look twice is worth ten times more than a neon explosion that makes them look away.

Now get out there and slay the gray.

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