The Blackburn Mars 4.0 is the brightest rear light in the range from Blackburn. It features a single super bright red LED pointing directly backwards and two smaller orange LEDs for visibility from the sides. It’s a compact lightweight unit and offers a number of mounting options.

Manufacturers specifications

Blackburn’s most powerful rear flasher
1 Watt Ultra Bright Red LED
2 Amber Side LED’s for lateral visibility
50 hour run time steady; 150 hour run time flash
No tool battery installation
2 AAA batteries included
3 mounting options included: belt clip, seat post clamp and reflector/rear rack mount
Lifetime Warranty


Best Rear Bike Light - Blackburn mars
Best Rear Bike Light – Blackburn mars

The Blackburn Mars 4.0 is about the size of a small matchbox which weighs only 58g including batteries. It’s made of tough plastic appropriate for the rough conditions these lights need to endure in daily use. Opening the case to change the battery will cost you a penny – a quick twist of which in the slot at the base of the unit prizes the case apart. A rubber seal is effective at keeping out the rain.

Mounting Options

Best Rear Bike Light - Blackburn mars
Best Rear Bike Light – Blackburn mars seatpost mount

A number of options exist for mounting the light to the bike. Most people will choose to mount the light on the seat post. The included mount wraps around a seat post of any shape or diameter. The vertical angle can be adjusted and it’s worth spending a little time getting the angle just right to ensure maximum visibility to a range of road users from cars to lorries. The clip on the rear of the light used for attaching to the seat post mount doubles up as a belt clip. A further mount is also included which allows the light to be attached to a rear rack.

The Mars 4.0 is an excellent choice for Brompton owners. It fits nicely to the seat post and doesn’t affect the folded package apart from the seat post protruding an extra centimetre.

Operating Modes

The Blackburn Mars 4.0 light is operated by a single push button on the top. The button is quite small and is tricky to operate with gloves – though with some practise it can be done. One press of the button switches the light on in steady mode. A second press puts the light into flashing mode. A third press switches the light off. All nice and simple!

Beam Pattern and Brightness

Blackburn Mars Beam Patterns
Blackburn Mars Beam Patterns

The light has a circular beam pattern which is bright over quite a wide viewing angle. With fresh batteries the Mars 4.o is at least as bright as our benchmark Cateye TL-LD1100 from the rear but while it does include side LEDs is not as bright as the Cateye from the sides. None the less it kicks out an impressive light for one so small.

Battery Life

As always I recommend the use of rechargable batteries and with AAAs, make sure you get a pair with a rating of 800mAh or greater. In my test using a pair of 850 mAh batteries (which had a measured capacity of 700mAh), the batteries lasted for approx 35 hours on steady mode before the light has finally extinguished. The brightness dropped off quite quickly though so I would say that you would probably want to be recharging the batteries after around 12 hours use (longer on flashing) to maintain maximum visibility. When I was using this light last winter for an hour a day I got into the routine of charging the batteries every two weeks. To get the most from your batteries, be sure to use a good charger.


The Blackburn Mars 4.0 is a great little light and would be a good choice if you want something smaller and lighter than the TL1100 but don’t want to compromise on brightness. It’s our recommended rear light for Brompton users and is our choice for best lightweight rear light.

Where to buy the Blackburn Mars 4.0 Light

The Mars 4.o can be purchased from here or here.

The Official manufacturer website page for this light can be found here.

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