3mm Round Top Slow Flashing 1HZ LED

3mm slow-flashing LEDs (1Hz) blink once per second in the compact T-1 through-hole package that measures just 3mm across the lens.

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3mm slow-flashing LEDs (1Hz) blink once per second in the compact T-1 through-hole package that measures just 3mm across the lens. The built-in integrated circuit (IC) handles all flash timing automatically — no Arduino, no 555 timer, no external components beyond a standard current-limiting resistor. The one-flash-per-second cadence is the universal standard for railroad crossing signals, alarm indicators, and turn signal mockups, and the 3mm body is the natural choice when a 5mm LED would be physically too large for the application. Model railroaders building HO scale (1:87) and N scale (1:160) layouts overwhelmingly prefer 3mm over 5mm for signal heads, locomotive markers, and structure-mounted warning beacons, because the smaller form factor is proportionally correct at these scales. The 3mm body also fits the smaller bezel holes found in compact guitar pedal enclosures, miniature wargaming terrain, and tight electronic panel layouts.

HO and N scale railroad crossing signals: The 1Hz flash rate matches the cadence of real North American grade crossing flashers, making 3mm 1Hz LEDs the go-to choice for scratchbuilt and kitbashed crossing signals on HO and N scale layouts. A pair of red 3mm 1Hz LEDs mounted in a signal mast housing will naturally drift out of sync over several minutes, producing the alternating left-right flash pattern of a real crossbuck signal without any alternating relay circuit. Red 3mm 1Hz LEDs also serve as end-of-train device (ETD/FRED) markers on the last car of a freight consist, block signal aspects, and yard limit warning beacons. Amber 3mm 1Hz LEDs replicate the approach aspect of color-position light (CPL) signals. Model railroaders building British, European, and Japanese prototype layouts use 3mm 1Hz LEDs for their respective national signal systems, all of which use approximately 1Hz flash rates for warning aspects.

Guitar pedals, miniatures, and compact electronics: Stompbox builders who use 3mm panel-mount bezels instead of the more common 5mm size choose 3mm 1Hz LEDs as tap-tempo visual indicators, bypass flash markers, and effect-active status lights on custom guitar pedals. The blinking indicator draws attention to the active pedal on a crowded pedalboard without being as bright or visually dominant as a 5mm LED. Warhammer 40K and miniature wargaming hobbyists wire 3mm 1Hz LEDs into terrain pieces as blinking warning beacons on industrial buildings, landing pads, and fortification walls. The T-1 body hides inside a 28mm scale structure where a 5mm LED would protrude visibly. Slot car racers in 1:32 and 1:24 scale use red 3mm 1Hz LEDs as turn signal indicators on rally car and touring car models, and amber 3mm 1Hz LEDs as hazard flashers on emergency support vehicles. Drone builders mount red 3mm 1Hz LEDs as rear position lights for nighttime orientation.

Available colors and lens characteristics: We stock 3mm 1Hz slow-flash LEDs in red, orange, amber, yellow, green, blue, cool white, and warm white. All have a water-clear lens with a 15–30° viewing angle for maximum on-axis brightness (mcd). For wider-angle visibility, consider diffused 3mm LEDs (frosted lens, 120–160°) for applications where the LED must be visible from the side. White LEDs are available in warm white (~3000–4000K) for incandescent-like tones and cool white (~5500–6500K) for a crisp, modern appearance. Each product page lists the exact peak wavelength in nanometers for color-matching across a build.

Electrical specifications: Forward voltage by color: red/orange/yellow/amber ≈ 2.0–2.2V; blue/green/white/UV ≈ 3.0–3.2V. Maximum forward current: 20mA. A series current-limiting resistor is mandatory. Use our LED resistor calculator to find the correct value for your supply voltage. Common values: 12V → 510Ω for red, 470Ω for white/blue; 5V → 150Ω for red, 100Ω for white/blue. For DCC model railroad track power or AC transformers, add a bridge rectifier and smoothing capacitor to convert to DC — see the AC/DCC wiring guide. New to LEDs? Pre-wired LEDs include the resistor on the wire for plug-and-play operation.

3mm vs. other sizes at 1Hz: The same 1Hz slow-flash animation is available in 5mm (the most popular overall size), 10mm (for large-scale displays and G scale signals), and 1.8mm (the smallest through-hole size, for N and Z scale). All sizes share identical electrical specs — same forward voltages, same 20mA current, same resistor calculations. The only difference is the physical lens diameter and the resulting panel-mount hole size (3.2mm / 1/8″ for 3mm LEDs). Choose based on the physical space available and the scale of your project: 3mm for HO and N scale models, guitar pedals with 3mm bezels, and compact electronics; 5mm for general-purpose projects and breadboard prototyping.

Related categories: For other 3mm animated types, browse 3mm 2Hz fast flash, 3mm 6Hz extra-fast, 3mm 0.25Hz extra-slow, 3mm flickering candle, 3mm fading/breathing, and 3mm red/blue alternating. For static (non-flashing) 3mm LEDs, see 3mm round-top LEDs. For animated LEDs with a pre-attached resistor wire, browse animated pre-wired LEDs.

The only difference is physical size. A 3mm LED has a 3mm lens diameter (T-1 package) and fits a 3.2mm panel hole. A 5mm LED has a 5mm lens diameter (T-1¾ package) and fits a 5.2mm panel hole. Electrically they are identical — same forward voltage ranges by color, same 20mA maximum current, same resistor values. Choose 3mm for HO/N scale models, 3mm bezels, and tight spaces. Choose 5mm for general-purpose use, breadboards, and larger-scale projects.
Yes. When two identical 1Hz LEDs are powered on simultaneously, slight manufacturing differences in their internal oscillators cause them to naturally drift out of phase over several minutes. This produces a convincing alternating flash where one LED is on while the other is off. The effect requires no special wiring — just connect both LEDs to the same power source with their own resistors and the drift does the rest.
Use a 3.2mm or 1/8″ drill bit for a snug press-fit. For a professional panel-mount finish, use a 3mm LED holder or bezel — the LED snaps in from the front and locks from the back with a retaining ring. Holders are available in chrome and black finishes.
Yes. The internal IC controls only the flash timing, not the current. A series current-limiting resistor is required. Use our LED resistor calculator to find the correct value for your supply voltage and LED color.
Yes, but DCC is a form of AC and must be converted to DC first. Add a bridge rectifier and smoothing capacitor between the track bus and your LED circuit. See our AC/DCC wiring guide for a complete wiring diagram and component values.
Yes — a clear-lens red 3mm LED at 20mA produces hundreds to thousands of mcd, more than sufficient for a visible flashing signal at HO scale viewing distances (typically 2–4 feet). The focused 15–30° beam of the clear lens concentrates light toward the viewer, making the flash appear bright and crisp. If you want the signal to be visible from a wider angle, consider a diffused 3mm LED driven by an external flasher circuit, or sand the tip of a clear LED lightly with fine-grit sandpaper to diffuse the beam.