Bontrager Rear Light | High-Visibility Bike Safety Lights
Our Flare RT rear light sets the standard for daytime visibility with 90 lumens of focused flash output. We engineered this rechargeable tail light to keep you visible from up to two kilometers away, even in bright sunlight. The integrated light sensor automatically adjusts brightness based on ambient conditions, while the compact design mounts securely to any seatpost or saddle rail.
With five lighting modes and up to 20 hours of runtime on a single charge, the Flare RT adapts to every ride condition. The IPX7 waterproof rating ensures reliable performance through rain, mud, and spray.
Technical specifications & visibility details
Advanced Optics & Visibility Technology
Every bontrager rear light in our lineup features precision-engineered optics designed to maximize your visibility without wasting battery power. We use focused beam patterns that direct light exactly where drivers need to see it—creating a bright central hotspot while maintaining 180-degree side visibility. Our proprietary lens designs eliminate glare and concentrate output into attention-grabbing patterns that stand out in traffic.
The Flare RT’s focused beam technology projects light up to two kilometers in daylight conditions, making it visible even against bright morning or afternoon sun. We tested these lights extensively in real-world traffic scenarios to ensure they cut through visual noise—passing vehicles recognize the distinctive flash pattern immediately. Our Day Flash modes use strategically timed bursts that trigger the human eye’s motion detection response, making your presence unmistakable to motorists approaching from any angle.
Battery Performance & Charging
We equip our rechargeable rear lights with lithium-ion batteries rated for over 500 charge cycles, ensuring years of reliable service. The Flare RT and Flare R City use USB-C charging for fast, convenient power replenishment—a full charge takes just 2-3 hours from any standard USB power source. The Ion 100 R uses micro-USB connectivity, maintaining compatibility with existing charging cables many riders already own.
Battery indicator systems on every model provide clear status information before and during rides. The Flare RT displays a four-stage battery gauge that updates in real time, while the Ion 100 R and Flare R City use color-coded indicators that shift from green to red as charge depletes. Low-battery warnings activate with enough advance notice to complete your ride safely—the Flare RT begins flashing its power button 15 minutes before shutdown, giving you time to switch to a lower-power mode or wrap up your session.
Mounting Systems & Installation
Our rear lights use tool-free mounting systems that install in seconds and hold securely through rough terrain and high-speed descents. The Flare RT and Flare R City include a dual-position bracket that clamps to round or aero seatposts from 25.4mm to 31.8mm diameter. The same bracket also grips standard saddle rails, giving you mounting flexibility for bikes with limited seatpost exposure or integrated seat masts.
The Ion 100 R uses a silicone strap mounting system that wraps around virtually any tube diameter or profile. We reinforced the strap material to prevent stretching, and the ladder-lock buckle maintains tension through thousands of mount-and-remove cycles. This universal mounting approach works on seatposts, chainstays, helmet vents, and backpack straps—anywhere you need supplemental visibility.
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Common Questions About Bontrager Rear Lights
Runtime varies by model and mode selection. The Flare RT delivers up to 20 hours on All-Day Flash mode, 6 hours on Day Flash, and 4 hours on Day Steady. The Ion 100 R provides up to 14 hours on Eco Flash mode, 5 hours on Flash, and 3 hours on Steady. The Flare R City runs up to 6 hours on Day Flash and 3 hours on Night Flash.
Actual runtime depends on ambient temperature, battery age, and how frequently you cycle between modes. Cold weather reduces runtime by approximately 15-20% compared to room temperature operation. We recommend charging your light after every 4-5 rides to maintain consistent brightness and avoid unexpected shutdowns.
Yes, our Day Flash modes are specifically engineered for daytime visibility. The Flare RT produces 90 lumens in a focused beam pattern that remains visible from up to two kilometers away, even in direct sunlight. The Ion 100 R and Flare R City deliver 35 lumens with strategically timed flash patterns that trigger drivers’ motion detection response.
We tested these lights extensively in real-world traffic conditions to ensure they cut through visual noise during morning and afternoon commutes. The focused beam technology concentrates output into attention-grabbing patterns rather than dispersing light in all directions, making them significantly more effective than generic tail lights with similar lumen ratings.
The Ion 100 R’s silicone strap mounting system works excellently on backpack straps, messenger bags, and helmet vents. The universal strap design wraps securely around virtually any profile without requiring dedicated mounting points. Many commuters use it as a supplemental light on their backpack while keeping a Flare RT or Flare R City on their seatpost for maximum visibility.
The Flare RT and Flare R City require their included bracket, which is designed for round or aero seatposts and saddle rails. These models don’t adapt well to soft mounting points like backpack straps. For helmet mounting, we recommend checking whether your specific helmet model has compatible mounting points before purchasing.
The Flare RT is our premium model with 90-lumen maximum output, five lighting modes, an integrated light sensor that adjusts brightness automatically, and up to 20 hours runtime. It’s designed for riders who want maximum daytime visibility and advanced features. The Flare R City produces 35 lumens with two simplified modes (Day Flash and Night Flash) for commuters who prioritize straightforward operation.
Both models use USB-C charging, carry IPX7 waterproof ratings, and include the same dual-position mounting bracket. The Flare RT costs $20 more but provides significantly longer runtime and greater visibility range. The Flare R City offers excellent value for recreational riders and urban commuters who don’t need extreme output levels.
All our lights include battery status indicators with low-charge warnings. The Flare RT displays a four-stage battery gauge that updates continuously, and the power button begins flashing 15 minutes before shutdown. The Ion 100 R and Flare R City use color-coded indicators—green shows full charge, amber indicates medium charge, and red signals low battery.
We calibrate these warnings to provide adequate notice for completing your ride safely. When you see a low-battery indication, you typically have 30-60 minutes of runtime remaining depending on your selected mode. Switching to a lower-power mode immediately after the warning extends this buffer significantly.
The Flare RT and Flare R City carry IPX7 waterproof ratings, meaning they survive full immersion in one meter of water for 30 minutes. This protection level handles torrential rain, wheel spray, bike washing, and muddy conditions without any performance degradation. The Ion 100 R has an IPX4 rating that protects against heavy splashing and rain from all directions, suitable for most riding conditions.
All models feature sealed USB port covers with double-lip gaskets that prevent moisture intrusion even when charging ports face upward in rain. We recommend wiping port areas dry before opening covers for charging, but the internal seals provide backup protection. Conformal coating on internal circuit boards prevents corrosion if moisture does penetrate the housing.
Many riders run two rear lights simultaneously for redundancy and increased visibility. Common configurations include a Flare RT on the seatpost paired with an Ion 100 R on a chainstay or backpack strap. This setup provides 360-degree visibility and ensures you’re never left without a working light if one battery dies unexpectedly.
There’s no functional interference between multiple lights—they operate independently and don’t affect each other’s performance. For maximum safety, position lights at different heights and angles to create a larger visual profile that’s easier for motorists to recognize as a cyclist rather than a single point of light.