5mm Round Top LED

5mm round-top LEDs (T-1¾ package) are the most widely used LED size in the world and the default starting point for virtually every through-hole LED project.

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5mm round-top LEDs (T-1¾ package) are the most widely used LED size in the world and the default starting point for virtually every through-hole LED project. The 5mm form factor is the standard for Arduino prototyping, breadboard circuits, panel indicators, automotive accent lighting, model railroading, guitar pedal builds, cosplay props, escape room puzzles, Halloween displays, and Christmas lighting. If you are not sure what size LED to order, 5mm is almost always the right choice. We stock 5mm clear round-top LEDs in every standard color: red, orange, amber, yellow, green, blue, cool white, warm white, UV, pink, and RGB color-cycling variants.

Who uses 5mm round-top LEDs? Arduino and electronics hobbyists use them for every introductory circuit — the classic “blink an LED” tutorial starts with a 5mm red LED and a 220Ω resistor. Model railroaders in O, HO, and S scale use cool white 5mm LEDs for locomotive headlights and warm white for building interiors and station platform lights. Guitar pedal builders on DIYPB, freestompboxes.org, and r/diypedals wire red or blue 5mm LEDs as bypass indicators in 1590B and 125B enclosures. Automotive enthusiasts replace stock dash bulbs with 5mm LEDs for gauge cluster accent lighting, cup holder illumination, and door panel effects. Cosplay builders embed 5mm LEDs in Iron Man arc reactors, lightsaber hilts, and Mandalorian helmet visors. Escape room designers use colored 5mm LEDs behind puzzle panels as solve-state indicators visible from across a dim room. Halloween prop builders wire red 5mm LEDs into foam skulls, green LEDs into witch cauldrons, and UV LEDs behind fluorescent-painted walls in haunted house walk-throughs.

Colors, wavelengths, and lens characteristics: All 5mm round-top LEDs in this category have a water-clear lens that focuses light into a tight 15–30° forward beam, producing the highest on-axis brightness (mcd) of any 5mm package. Each product page lists the peak wavelength in nanometers — essential for color-matched indicator arrays, scientific optical setups, and RGB mixing experiments. White LEDs come in two temperature ranges: warm white (~3000–4000K) for a soft, incandescent-like glow suited to accent lighting and warm-toned displays, and cool white (~5500–6500K) for a crisp, blue-leaning white ideal for task lighting, headlights, and instrument panels. UV LEDs (395–405nm) activate fluorescent paint, detect counterfeit currency, and cure UV-set adhesives. Need wider-angle light distribution instead of a focused beam? See our diffused 5mm LEDs (frosted lens, 120–160°) or 5mm straw hat LEDs (flattened dome, 120–140°).

Electrical specs and resistor selection: Forward voltage by color: red/orange/yellow/amber ≈ 2.0–2.2V; blue/green/white/UV ≈ 3.0–3.2V. Maximum forward current: 20mA. Every bare LED must have a series current-limiting resistor — without one, the LED draws uncontrolled current and burns out in seconds. Common values: 12V supply → 510Ω for red, 470Ω for white/blue; 5V (Arduino) → 150Ω for red, 100Ω for white; 9V battery → 330–470Ω depending on color. Use our LED resistor calculator for any supply voltage. For series wiring at 12V, you can chain two red LEDs (2V + 2V = 4V drop) with a 390Ω resistor, or three blue/white LEDs (3.1V × 3 = 9.3V drop) with a 150Ω resistor — series wiring is more power-efficient and ensures equal current through each LED. Running from AC (model railroad transformers, DCC track power, or 12V landscape lighting wire)? Add a bridge rectifier and smoothing capacitor to convert to DC first. See the AC/DCC wiring guide for a complete diagram. New to LEDs? Pre-wired LEDs are the easiest starting point — the resistor is already built in, so you just connect power and ground.

Mounting and physical dimensions: The 5mm LED body fits a 5.2mm (13/64″) panel-mount hole for a snug friction fit. For a professional panel installation, use a 5mm LED holder or bezel — the LED clicks in from the front and locks from the back. Lead spacing is 2.54mm (0.1″), compatible with solderless breadboards, perfboard, and standard-pitch PCBs. The longer lead is the anode (+); the shorter lead with a flat on the base is the cathode (−). The 5mm package is also the standard size for coupling light into fiber optic strands — the clear lens focuses the beam directly into the fiber end for pinpoint illumination in dioramas, architectural models, and starfield ceilings.

Choosing the right 5mm LED shape: Round-top (this category) gives the tightest beam and highest on-axis mcd — best for headlights, spotlights, fiber-optic coupling, and any application where the LED points directly at the viewer. Flat-top 5mm LEDs spread light across 100–160° for panel backlighting and gauge clusters. Straw hat 5mm LEDs have a flattened dome for 120–140° area lighting. Flat-top concave 5mm LEDs refract light outward for near-omnidirectional emission, ideal for Christmas string light replacements. All four shapes share the same 5mm base, same electrical specs, and same resistor values — the only difference is how the lens shapes the beam.

Related categories: For a smaller footprint, see 3mm round-top LEDs (T-1 package). For the largest through-hole option, browse 10mm round-top LEDs. Want automatic flashing or color-cycling without a microcontroller? Browse animated LEDs. For plug-and-play installation at 5V, 6V, 9V, or 12V, see pre-wired LEDs. For a 12V circuit without calculating resistors, 12V built-in resistor LEDs are a drop-in solution. Surface-mount projects use SMD LEDs down to 0402 package. Multi-color mixing uses RGB LEDs with separate red, green, and blue dies in a single package.

Frequently Asked Questions

Forward voltage (Vf) depends on the LED color. Red, orange, amber, and yellow LEDs typically need 2.0–2.2V. Blue, green, white, UV, and RGB LEDs typically need 3.0–3.2V. The exact Vf is listed on each product page. Your supply voltage must exceed Vf for the LED to light — the remaining voltage is dropped across the current-limiting resistor.
It depends on your supply voltage and the LED color. Use our LED Resistor Calculator to find the exact value for your supply voltage and LED color.020A. At 12V: red ≈ 510Ω, white/blue ≈ 470Ω. At 5V (Arduino): red ≈ 150Ω, white/blue ≈ 100Ω. At 9V (battery): red ≈ 330Ω, white/blue ≈ 300Ω. Use our LED resistor calculator for any voltage, or check the resistor table on each product page. If you prefer zero math, pre-wired LEDs and 12V built-in resistor LEDs include the resistor already.
Use a 5.2mm or 13/64″ drill bit for a snug friction fit. A standard 3/16″ (4.76mm) bit is slightly too small; a 7/32″ (5.56mm) bit gives a loose fit better suited for use with a snap-in LED holder or bezel. LED holders are available in chrome and black and provide a clean panel-mount finish without adhesive.
The number is the lens diameter. 5mm (T-1¾) is the most popular — bright, available in every color and lens style, and compatible with the widest range of holders and bezels. 3mm (T-1) is for tight spaces and smaller-scale models (HO, N scale, slot cars). 10mm is for large panel indicators, G-scale railroads, and 1:10 scale RC headlights where the LED body needs to fill a bigger space. All three sizes share the same electrical specs: same forward voltage ranges by color, same 20mA max current, same resistor formulas.
LEDs require DC power. On raw AC, they flicker at line frequency and the reverse voltage half-cycle can damage them over time. For 12V AC landscape transformers or DCC track power, add a bridge rectifier to convert AC to DC, plus a smoothing capacitor to flatten the waveform. Our AC/DCC wiring guide has a complete diagram with component values.
Clear-lens round-top LEDs (this category) focus light in a narrow 15–30° beam with the highest mcd brightness rating — extremely bright head-on, dim from the side. Best for headlights, spotlights, and fiber optic coupling. Diffused LEDs have a frosted lens that scatters light over 120–160°, producing a soft, even glow visible from any angle. Best for panel indicators, signal lights, building interiors, and anywhere the LED needs to be seen from multiple directions. Both types share the same electrical specs and resistor values.