5mm Round Top Slow Flashing 1Hz LED

5mm slow-flashing LEDs (1Hz) blink on and off exactly once per second — one full flash cycle every 1,000 milliseconds.

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5mm slow-flashing LEDs (1Hz) blink on and off exactly once per second — one full flash cycle every 1,000 milliseconds. A tiny integrated circuit (IC) built into the LED package handles all timing internally, so there is no need for an Arduino, 555 timer, external flasher module, or any programming whatsoever. Connect a current-limiting resistor and a DC power source, and the LED begins its steady one-second cadence the instant power is applied. The 1Hz rate is the most universally recognized flash frequency — it matches the blink rate of railroad crossing signals, automotive turn indicators, alarm panel warning lights, and nearly every “caution” flasher in daily life. That familiarity makes 1Hz slow-flash LEDs the single most popular animated LED type we sell, and the default choice when a project calls for a blinking light without specifying a rate.

Model railroad crossing signals and beyond: The 1Hz flash rate is the prototypical cadence of North American grade crossing flashers, making these LEDs the natural choice for HO, N, O, and G scale crossing signal builds. Wire a pair of red 5mm slow-flash LEDs into a crossbuck signal housing and they will naturally drift out of sync over a few minutes, producing the characteristic alternating left-right flash that real crossing signals use — no alternating relay circuit needed. Beyond crossings, 1Hz red LEDs replicate the steady blink of end-of-train devices (ETDs), block signal aspects, and yard limit markers. Amber 1Hz LEDs serve as advanced approach signals. Green 1Hz LEDs simulate flashing approach signals on CTC-controlled mainlines. Model railroaders building N scale layouts favor the 3mm or 1.8mm versions of this same animation (see related categories below), but the 5mm body is correct for O and G scale signal heads and for structure-mounted warning beacons where a larger, more visible flash is appropriate.

Safety markers, alarm panels, and indicator lights: Outside model railroading, 1Hz slow-flash LEDs are widely used as visual alarm indicators in DIY security panels, smoke detector test circuits, and equipment fault displays. The once-per-second blink is universally understood as “attention needed” without being as aggressive or startling as a faster strobe. Bicycle commuters and nighttime runners mount red 1Hz flash LEDs in handlebar housings and vest clips for visibility at intersections. Amateur radio operators use amber 1Hz LEDs as transmit indicators on homebrew rigs. Escape room builders wire 1Hz LEDs behind translucent panels as puzzle-state indicators — a blinking red LED signals an unsolved lock, while a steady green LED (static, non-flashing) signals a solved state. Halloween prop builders use red 1Hz LEDs as blinking eyes in skull and skeleton displays, and amber 1Hz LEDs as lantern flicker accents on porch setups where the faster candle-flicker LED would be too chaotic.

Available colors: We stock 5mm 1Hz slow-flash LEDs in red, orange, amber, yellow, green, blue, white (cool and warm), pink, UV, and multi-color RGB cycling variants. All have a water-clear lens with a 15–30° viewing angle for maximum on-axis brightness (mcd). For wider-angle visibility, pair with a diffusing cap or check our diffused LED category for static wide-angle alternatives. White LEDs come in two color temperatures: warm white (~3000–4000K) for a soft, incandescent appearance, and cool white (~5500–6500K) for a bright, crisp flash. The red/blue alternating variant is listed separately under 5mm red/blue alternating LEDs since it contains two separate dies.

Electrical characteristics and wiring: Forward voltage follows standard LED color ranges: red/orange/yellow/amber ≈ 2.0–2.2V; blue/green/white/UV ≈ 3.0–3.2V. Maximum forward current: 20mA. The internal IC consumes negligible current — brightness during the “on” phase is essentially identical to a standard static 5mm LED of the same color. A series current-limiting resistor is mandatory. Use our LED resistor calculator to find the exact value for your supply voltage and LED color. Common values: 12V supply → 510Ω for red, 470Ω for white/blue; 5V → 150Ω for red, 100Ω for white/blue. For AC power sources (model railroad transformers, DCC track power, 12V landscape wire), add a bridge rectifier and smoothing capacitor to convert to DC before the LED circuit — see the AC/DCC wiring guide. New to LEDs? Pre-wired LEDs come with the resistor already attached for plug-and-play operation.

1Hz vs. other flash rates: The 1Hz rate sits at the calm, measured end of the flash spectrum. If you need more urgency, step up to 2Hz fast flash (two blinks per second) for construction barricade and bicycle safety applications, or 6Hz extra-fast flash (six per second) for emergency strobe simulation. If you want an even subtler pulse, 0.25Hz extra-slow flash blinks once every four seconds — the gentle standby indicator cadence. For non-repeating organic movement, consider flickering candle LEDs (random flame simulation) or fading/breathing LEDs (smooth ramp up and down). All animated LED types share the same forward voltage, current, and resistor requirements — the only difference is the IC program.

Related categories: This same 1Hz slow-flash animation is available in 3mm, 1.8mm, and 10mm through-hole sizes, as well as 0807 SMD and 0603 SMD surface-mount packages. For static (non-flashing) 5mm LEDs, see 5mm round-top LEDs. For animated LEDs with the resistor pre-soldered to a wire lead, browse animated pre-wired LEDs. For multi-color effects under your own control, see RGB LEDs.

1Hz means one complete on-off cycle per second. The LED is on for approximately 500 milliseconds, then off for approximately 500 milliseconds, repeating continuously. This is the standard “slow blink” rate — the same cadence used by real railroad crossing signals and automotive turn indicators. It is fast enough to be clearly noticed as a blinking light, but slow enough to appear calm and non-urgent.
Yes. The internal IC controls only the flash timing, not the current. You must use a series current-limiting resistor just as you would with any standard LED. Without one, the LED will draw uncontrolled current and burn out immediately. Use our LED resistor calculator to find the correct resistor value for your supply voltage and LED color. If you prefer no soldering or math, our animated pre-wired LEDs include the resistor on the wire.
Yes. When you power on two identical 1Hz LEDs at the same time, they start in approximate sync, but the slight manufacturing variation in each LED’s internal oscillator causes them to drift apart naturally over several minutes. This drift produces a convincing alternating flash pattern without any special wiring — one LED is on while the other is off, then they swap. For model railroad grade crossing signals, this natural drift effect is realistic and requires zero additional components beyond the LEDs and their resistors.
Approximately 50% — the LED spends roughly equal time in the on and off states within each one-second cycle. This means the LED is illuminated about half the time, which cuts average power consumption roughly in half compared to a continuously lit static LED of the same color and brightness. The actual on/off ratio may vary slightly by manufacturer lot, but it is close enough to 50/50 that it appears as a balanced, symmetric blink to the human eye.
Yes. During the “on” phase of each flash cycle, a 1Hz animated LED produces the same brightness (mcd) as a standard static 5mm LED of the same color and lens type. The internal IC simply switches the LED on and off — it does not reduce drive current or dim the output. The mcd rating listed on the product page reflects peak (on-state) brightness. Perceived average brightness over time is lower because the LED is off half the time, but each individual flash is full intensity.
Yes, but you need to convert DCC track power to DC first. DCC is a form of alternating current, and LEDs require DC. Add a bridge rectifier and a smoothing capacitor between the track bus and your LED circuit. The same applies to 12V AC landscape transformers. See our AC/DCC wiring guide for a complete wiring diagram and component values. Once converted to clean DC, the flashing LED works exactly as it would on a DC power supply or battery.