Best Rear Bike Lights: Radar, Brake-Sensing and Budget

For a plain light that shows up in daylight, we would buy the Cateye ViZ450 at about $50. Its day flash is 450 lumens and Cateye says it lasts 14 hours. If you want to know about cars coming up behind, Garmin’s Varia RearVue 820 at about $300 is the radar pick, because it runs 24 hours in day flash and works as a brake light too. The cheapest radar light here is Magicshine’s SEEMEE R300 at about $130.

The figures below are the makers’ own. We compared their spec sheets and store prices, and nothing here is a claim about how a light looks on the road.

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Rear lights compared

Prices are from each maker’s US store, rounded, except Exposure, which sells from the UK in pounds. Run times are the maker’s shortest and longest modes.

Plain lights

• Knog Plus Rear, about $22. A 17-gram strip of 20 lumens that mounts on the seat post or clips to a bag or jacket. Knog gives 2 hours steady and 40 hours in eco flash. It plugs straight into a USB-A socket to charge. Buy it as a second light, or for lit city streets. Knog Plus Rear on Amazon
• Cateye ViZ450, about $50. Four modes: constant at 40 lumens for 5 hours, flashing at 40 lumens for 65 hours, group ride at 20 lumens for 10 hours, and the 450-lumen daytime flash for 14 hours. It weighs 45 grams and its bracket fits aero seat posts. The weak point is water resistance, at IPX4. Cateye ViZ450 on Amazon
• Lezyne Strip Drive Pro 400+, about $60. The current version of the Strip Drive Pro from our old list. Ten LEDs, 400 lumens at most, seven modes, up to 80 hours, 71 grams, and a strap that fits round or aero posts. Lezyne does not include a USB-C cable. Lezyne Strip Drive Pro 400+ on Amazon
• Knog Blinder Link, about $65. It bolts under the saddle or onto the back of a rack, so a seat bag or pannier cannot hide it. The high flash is 100 lumens for 7 hours and the eco flash runs past 50. Knog Blinder Link on Amazon
• Trek Flare RT, about $70. Sold as the Bontrager Flare RT when we first listed it, and still 90 lumens. Trek gives flash modes of 90 lumens for 6 hours, 45 for 12 and 5 for 15, and steady modes of 25 lumens for 4.5 hours and 5 for 13.5. A sensor adjusts brightness to the light around you, and it weighs 40 grams. Trek Flare RT on Amazon

Lights that react when you brake

These detect the bike slowing and flare to warn whoever is behind. They work from a sensor inside the light, with no wire to the brake lever.

• Magicshine SEEMEE 300, about $55. 300 lumens, an aluminium body at 80 grams, and both a seat post and a saddle mount in the box. Magicshine says the brake function can be switched off, and a light sensor adjusts brightness. It is the cheapest brake-sensing light here by $15. Magicshine SEEMEE 300 on Amazon
• Lezyne Strip Pro Ai Alert 400+, about $70. The Strip Drive Pro with brake sensing added. Lezyne says it switches to a rapid 150-lumen flash when it detects you slowing. Lezyne Strip Pro Ai Alert 400+ on Amazon
• Exposure TraceR 4 ReAKT, £75. A machined aluminium light of about 35 grams from a British maker. Exposure says it brightens under braking and when daylight gets stronger, then dims for a rider sitting close behind. It charges by USB-C in 90 minutes. The plain TraceR 4 without the sensors is £55. Exposure TraceR ReAKT on Amazon

Lights with radar

A radar light watches the road behind and sends a warning to a bike computer or a phone app when a vehicle approaches. It is no use without one of those on the handlebar, so count that in.

• Magicshine SEEMEE R300, about $130. Radar to 140 metres, 300 lumens, and a flash that gets brighter by itself as a vehicle closes. It pairs with cycling computers over ANT+. At 113 grams it is not light. Magicshine SEEMEE R300 on Amazon
• Lezyne Radar Drive, about $180. Radar to 150 metres, a 300-lumen day flash, Bluetooth and ANT+, and Lezyne’s own phone app. It weighs 144 grams and runs up to 20 hours. Lezyne Radar Drive on Amazon
• Trek CarBack, about $200. The longest stated range at 240 metres, with a 90-lumen day flash and a phone app that shows how far back a vehicle is. Trek puts the battery at 7 hours or more and gives no figure for each mode. Trek CarBack on Amazon
• Garmin Varia RTL515, about $200. Garmin’s older radar, still on sale. Garmin lists 140 metres of range, 65 lumens in day flash for 16 hours, 20 lumens solid for 6 hours, and 71 grams. Garmin Varia RTL515 on Amazon
• Garmin Varia RearVue 820, about $300. Range of 175 metres, 100 lumens in day flash for 24 hours, 25 lumens solid for 10 hours, a brake light and a USB-C port. Garmin says it also reports a vehicle’s size and its side-to-side position. Garmin Varia RearVue 820 on Amazon

Garmin sells two more. The Varia RCT715 adds a camera for about $400, and the eRTL615, about $300, has no battery and takes its power from an e-bike.

What to check before buying

• The run time in the mode you will use. A headline figure of 80 or 200 hours is for the dimmest mode. Cateye’s 450-lumen flash lasts 14 hours and Trek’s 90-lumen flash lasts 6, which is the fairer comparison.
• The charging port. Most are USB-C now, and several makers leave the cable out. Knog builds a USB-A plug into the Plus, so there is no cable to lose.
• The water rating. Garmin defines its IPX7 as surviving a metre of water for 30 minutes. Cateye’s IPX4 is the lowest in the table.
• The mount. Aero and D-shaped seat posts need the right bracket or shim. Garmin, Lezyne and Cateye say theirs are included. Exposure sells its saddle rail and aero brackets separately.

What the law asks for

Rules for bike lights differ from country to country, so check your own before you rely on a flashing mode. As one example, Rule 60 of the UK’s Highway Code says a cycle ridden at night must have a lit red rear light and a red rear reflector, and that flashing lights are permitted. Germany is stricter about the light itself. Lezyne marks most of the lights above as not approved under Germany’s StVZO rules and sells separate versions that are.

Which to pick

• One bright light for day and night: the Cateye ViZ450, unless you ride in heavy rain often, in which case the Lezyne Strip Drive Pro 400+ and its IPX7 rating.
• A brake light on a budget: the Magicshine SEEMEE 300.
• A seat bag or a rack in the way: the Knog Blinder Link.
• Radar for the least money: the Magicshine SEEMEE R300, if you already have an ANT+ bike computer.
• Radar for long rides: the Garmin Varia RearVue 820. The RTL515 saves $100 if 16 hours is enough.
• A spare in the pocket: the Knog Plus Rear.

If you ride with a phone on the bars, our guide to speedometer apps for Android covers the free ones.

Quick answers

How many lumens should a rear bike light have?

The lights here run from 20 to 450 lumens. Exposure’s view is that 200 lumens in a pulse is enough to show in daylight and 75 constant suits lit roads after dark, and that more is not always better. Garmin’s radar lights manage with 65 to 100.

Should I use a rear light in the daytime?

The makers build a mode for it. Cateye and Trek each say their day flash can be seen from up to 2km.

Is a radar rear light worth it?

It costs $130 to $300 against about $50 for a bright plain light. What you get for the difference is a warning of vehicles from 140 to 240 metres back, shown on a bike computer or phone.

Where should the rear light go on the bike?

The seat post, for most of these. If a saddle bag or rack blocks it, use a saddle rail or rack mount. Knog makes the Blinder Link in both forms for that reason.

How does a brake-sensing bike light work?

A sensor inside notices the bike slowing and the light flares for a moment. Lezyne, Magicshine, Exposure and Garmin all sell one.

Prices move, so confirm on the maker’s store before you pay.