Short answer: OSL (Object Source Lighting) is the technique of painting how a light source on the model itself, like a glowing sword, magic, a torch, a glowing eye, or lava, lights up its surroundings. You reach for it when you want a coloured, dramatic scene. Done right it's breathtaking; done wrong it ruins the model.
Here's the key idea: in OSL you don't actually paint the light, you paint the surfaces the light falls on. In other words, you depict the relationship between the source and every surface it illuminates. That's why the technique looks extraordinary in photos and on display, yet break one core rule and the whole illusion collapses at once.
What is OSL and what is it for?
At its simplest, OSL means pretending there's a light source on the model and painting how that light reflects onto its surroundings. Picture a blue power sword (a glowing energy blade), an orange torch, or a green vial of poison: that colour bounces onto every surface facing the source and adds narrative to the model.
The painter who popularised this technique in the miniature world is Victoria Lamb. As she notes on her own site, she was the first woman hobbyist to win a Slayer Sword, at 2001 Games Day Australia, with the diorama "The Rescue of Sister Joan," and that piece is recognised as one of the earliest examples of what we now call OSL.
So what is it for? In short, it turns a flatly lit model into a cinematic scene. A fireball in a wizard's palm, the reactor in a robot's chest, a sword glowing in the dark; OSL makes all of these believable. That said, it's an advanced, slow technique that demands real planning and many layers.
How does it work?
At heart, OSL rests on getting two things right: light planning and the colour-value relationship. Both are summed up by a single principle that Light Miniatures calls the "cardinal rule."
According to Light Miniatures, the golden rule of OSL is this: lit areas always look brighter than the surrounding unlit areas; but no lit surface can ever be brighter than the light source illuminating it.
Light planning: First, you decide on the source. Where does it sit, what colour is it, how strong is it? The crucial part here is that light weakens fast with distance; this is called falloff. So the surfaces nearest the source are very bright, and they darken quickly as they move farther away.
Colour and value: The light's colour reflects onto the surfaces it strikes. The nearest point is almost the pure, light version of the light's colour; toward the edges, that colour grows progressively darker and more saturated. Unlit surfaces, meanwhile, must stay dark, because what makes OSL believable is precisely the contrast between light and shadow.
Which method should you use?
The tool you build OSL with depends on the smoothness you're after and your experience level. There are three main routes, and they all apply the same logic, a halo plus falloff; only the way you apply it changes.
- Airbrush: This gives the smoothest halo. It's ideal for building the glow gradually, with feather-soft transitions. The logic is the same as in Blending with an Airbrush.
- Glazing (brush): This is the most controlled method. You ease the light colour onto the surface in thin, transparent coats. It's the choice for display and competition work; see how it works in Glazing.
- Drybrush: This is the fastest, most beginner-friendly route. You lightly drag the light colour over raised areas for a rough but effective OSL; for the basics, see Drybrushing.
For your first attempt, though, the safest route is the glaze-based method: slow but forgiving, because you advance one controlled coat at a time and can gently correct any slip.
How do you do it, step by step?
The sequence below is the classic glaze-based, brush-applied OSL workflow. It's unhurried, gradual, and forgiving; you wait for drying between every coat.
- Paint the source first. The very first job is the light source itself: the brightest point should be an almost-white core, surrounded by a coloured halo. Remember, the source has to be the brightest spot on the model.
- Map the affected area. Now mentally mark the surfaces facing the source. Only these will catch the light; anything turned away from the source stays dark.
- Apply coloured glaze coats. Lay the light colour on with glazes, most intense nearest the source and fading as you move away. At this stage, deliberately exaggerate the falloff; a harder fade than your eye expects often reads as more believable.
- Place the brightest points. On the raised areas closest to the source, add the light colour pulled almost to white. These are the highlights that pull the eye to the source.
- Protect the shadow. Finally, surfaces that don't catch light must stay dark. Don't paint the whole model in the light colour; the moment the contrast disappears, so does the OSL.
Which paints and brushes?
OSL doesn't demand a special paint; well-thinned, saturated acrylics and a patient hand are usually enough. Even so, a few materials make the job noticeably easier.
- Saturated acrylics: Citadel, Vallejo, Scale75, Kimera, Army Painter. Clean, vivid colours like blue, orange, and green give the strongest OSL; pastel or muddy tones weaken the glow.
- Glaze medium: Citadel Lahmian Medium, Vallejo Glaze Medium, or a brand's own medium. Thin the light colour with medium rather than water alone and you avoid tide marks (the coffee-ring stain left as it dries) and blotchy drying.
- White and a light tone: For the core brightness you need the light colour pulled almost to white; keep it ready in a separate well.
- Brush: A size 1 or 2 synthetic-sable blend that holds a fine point is plenty. After all, in glaze-based OSL, controlling the fluid at the tip matters more than the brush brand.
- Wet palette: A very thinned glaze dries fast, so a wet palette that keeps the mix stable is a real lifesaver.
- Airbrush: Worth it if you want a genuinely smooth halo, because the soft gradient of a glow is hard to catch with a brush alone.
Most common mistakes
Almost every OSL mistake falls under one of two headings: breaking the golden rule and skipping the falloff. Here are the usual suspects:
- Painting a surface brighter than the source. No lit area can be brighter than the source; the moment you break this rule, the illusion shatters.
- No falloff. Spreading the light evenly everywhere creates an artificial look where the source seems to light every surface equally. That's why distance-based fade is essential.
- Breaking the single-source principle. Adding several conflicting light sources easily leads to chaos; at least to begin with, stick to one clear source.
- Spreading the light colour too wide. If you paint the whole model in the light colour, contrast dies and the scene flattens; the colour must stay only on surfaces facing the source.
- Lightening the shadow. Leaving the unlit side timidly light kills the glow's impact; the dark zone should stay boldly dark.
Pro tips
The gap between knowing the technique and getting good results from it often hides in these small habits.
- In real life, hold a coloured light over objects in a dark room and watch how it falls; observation is always the best reference.
- On your first attempt, choose one strong, coloured source. A blue power sword is a classic, forgiving start.
- Before you begin, it's worth watching Vince Venturella's "Hobby Cheating 145" video; it's one of the foundational OSL references.
- OSL looks more impressive in a photo than in person. So, for display and photography, set the light and background to suit it; a dark background pushes the halo forward.
- Build volume with normal lighting first, then add OSL on top. A solid Zenithal Priming and Layering foundation carries the OSL that sits over it.
- Its logic is close to NMM; studying how to read coloured reflections in NMM: Non-Metallic Metal sharpens your OSL eye too.
Frequently Asked Questions
What's the difference between OSL and real LED lighting?
The core difference is this: OSL fakes light with paint, so there's no actual light on the model and the illusion is pure brushwork. A real LED, by contrast, is a physical light source embedded in the model. The two actually complement each other nicely. For the physical version, see LED Source Lighting.
Is OSL too hard for beginners?
It's an advanced technique, true; but with the drybrush version a beginner can still get a believable result. The keys are three: choosing one strong source, exaggerating the falloff, and keeping the shadow dark. Try a small source first, like a blue sword; it's far easier than trying to cover the whole model.
What's the easiest method for OSL?
The fastest, most forgiving method is drybrush: you lightly drag the light colour over raised areas, rough but effective. By contrast, the smoothest result comes from an airbrush, the most controlled from glazing. For a first attempt, starting with drybrush and then cleaning up with glazes is a sensible route.
Which colour works best as the light colour?
As a rule, clean, saturated colours give the strongest effect: blue (magic, energy), orange (fire, torch), green (poison, radiation). Pastel or muddy tones, on the other hand, weaken the glow. Choose the colour to match the scene's story; a fireball should be orange, cold magic blue.
What should I build the OSL halo with?
The cleanest halo is built with glazing, easing the light colour on in very thinned, transparent coats. If you want an even smoother gradient, switch to an airbrush. Since catching the soft edge of a halo with a brush alone is hard, display work usually favours glazes or an airbrush.
At which stage of normal painting should I do OSL?
Almost last. Finish the model under normal lighting first, with standard shadows and highlights; OSL then goes on top as a final layer. The reason is simple: OSL overrides the existing light-and-shadow scheme and dominates it. So build the volume first, then add the light source's effect.
What is falloff and why does it matter so much?
Falloff is light weakening fast with distance. In practice, the surface nearest the source is very bright, while a little farther out is clearly dark. Skip it and spread the light evenly, and the scene looks artificial and flat. Applying the falloff a touch harder than you actually see, on the other hand, makes OSL more believable.
Key takeaway: In the end, the whole secret to OSL hides in one rule: light bright, shadow dark, no surface brighter than the source. Pick one clear source, exaggerate the falloff, keep the light colour only on surfaces facing the source, and leave the shadow boldly dark. With patient layers, this technique turns an ordinary model into a cinematic scene.
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