Choosing the right LED size is the first decision in any model lighting project, and it is easy to get wrong. A light that is too big will not fit inside the model, while one that is too small may not give enough glow. This guide explains how to match LED size to scale, which sizes suit common uses and how to place them for the best effect.

Why size matters

Scale models leave very little room inside. A room in a dollhouse, a cockpit in an aircraft model or a lamp on a railway station is measured in millimetres. The LED, its wire and any resistor have to fit in that space without bending the walls or showing through the surface. Size also affects realism. A lamp that is out of scale makes the whole model look wrong, even if every other detail is perfect.

Common LED sizes

Hobby LEDs come in a few standard sizes, measured by the diameter of the lens or the dimensions of the chip.

  • Chip and nano sizes, measured in fractions of a millimetre, suit very small scales and tight spaces such as vehicle headlights and tiny lamps.
  • Sizes around 1.8 mm to 2 mm suit small models, signals and details in the smaller railway scales.
  • The 3 mm size is a popular all rounder for buildings, vehicles and displays.
  • The 5 mm size suits larger models, signs and props where space is not tight.

As a rule, choose the smallest LED that still gives enough light. Smaller parts are easier to hide and can be placed in more positions.

Match the size to the model scale

Think about what a real light of that type would measure at your scale. A real streetlamp bulb may be a few centimetres across, which becomes a fraction of a millimetre in a small scale model. A headlight on a vehicle at 1:43 scale is only a few millimetres wide, so a chip or nano LED fits best. Larger scales such as 1:24 can take a 3 mm LED with room to spare.

For interiors, think about the room as a whole. A single small LED placed near the ceiling usually lights a model room better than several lights spread around, and it reduces wiring.

Consider the wire as well

The wire attached to an LED can limit where it fits. Thick wire is hard to hide and can pull the part out of position. Look for fine, flexible wire, which can pass through small holes and bend around corners. The Evan Designs page on information about LED sizes lists common dimensions, which is helpful when checking whether a part will fit in a planned space.

Light spread and brightness

Size is not the only factor. The viewing angle affects how the light spreads. A narrow angle gives a focused beam, useful for headlights and spotlights, while a wide angle spreads light across a room. A bright LED close to a thin wall may cause a hot spot, so consider a diffuser or a small gap between the LED and the surface.

Colour matters too. Warm white suits homes and street lamps, cool white suits modern buildings and instruments, and red, green or amber suit signals and indicators.

Plan placement before buying

Measure the space inside your model before choosing parts. Allow room for the LED, the wire route and any connectors. Mark each location on a drawing and count how many lights you need. Planning first stops you from buying parts that do not fit and makes it easier to decide where wires will exit the model.

A quick decision guide

  • Tiny details and tight spaces: chip or nano LEDs.
  • Small scale buildings and signals: 1.8 mm to 2 mm LEDs.
  • General purpose lighting: 3 mm LEDs.
  • Large models and props: 5 mm LEDs.

Learn more about sizing

For a deeper look at this topic, see the Evan Designs article on the best size LED for your scale model. It pairs well with a careful measurement of your own project.

When in doubt, order one size smaller than you think you need and test it in the model. It is far easier to add brightness or a second light than to make room for a part that is too large.