The Exposure Sirius Mk4 has gained another 100 lumen over its predecessor but there is more to it than just pure power. It's a clever little light that is good enough to be used on its own, as a backup or getting the commuter noticed year-round, all in a small, lightweight package.
UK brand Exposure has a huge range of lights, and the Sirius sits in amongst the smaller mini torch shaped ones like the legendary Joystick (we tested the Mk 10 last month). They all follow the same design, a one-piece, CNC machined alloy body with an internal battery. It makes for a compact unit and the Sirius weighs just 79g including its plastic bracket and rubber o-ring fixing.
Up front you get a single LED, which on its maximum setting pumps out 500 lumen for two hours from the single 2,600mAh lithium ion battery or 36 hours on its lowest. With seven different settings on offer, thanks to Exposure's Optimum Mode Selector you can tweak the Sirius to emit the brightness/burn time ratio you require.
It's simple to set up: you just press and hold the on/off button until the number of flashes corresponds with the setting number. They're printed on the bottom of the light so you don't need to memorise them. With all of the settings you also get the pulse function if you hold the on button for just a little longer than normal.
You can keep an eye on the juice level by the colour of the on/off button – it changes from green to amber to red as the charge drops. A charge time of four hours from completely flat means that most people could charge it up at work to avoid getting caught out on your next ride. The light comes with a USB charger cable.
It's in the urban environment that it works best. The bright white light stands out in the orange hue of streetlighting in any mode, but as a commuter I would tend to have it on pulse more often than not as it is really eye-catching without being antisocial, especially when filtering through busy streets. In pulse mode the LED stays on the whole time on a low mode while emitting a stronger 'flash' at a constant pace. It's bright enough to work in daylight too.
Fitting is easy: a simple curved bracket for the light to be pushed into holds things firm, with a ladder style o-ring keeping it in position on the bar. It makes for simple attaching and removing should you need to leave your bike during the day in public. The light body can sometimes slide forward because of vibration but it's not really a problem.
On unlit roads the beam is usable if not really ideal, as it is very focused in the centre without much light thrown to the sides. You can still ride at a decent pace though – on dark lanes I was quite comfortable up to around 25mph with regards to seeing potholes and the like, though you can knock 5mph off that if the surface is wet and less reflective.
The Sirius comes with the same Smart Port Technology as the rest of the range. You can plug things into the rear charge port, such as Exposure's Red-Eye rear light or piggyback batteries, which can make the light quite versatile.
The charge port does always have a small amount of power going to it even if it's not being used, so you need to make sure the rubber cover is closed if you are riding in the rain. Earlier lights didn't have this cover and they could short out, returning to normal once dried out. I've never had this issue with my own Sirius Mk1 or this latest version, mind, and it's seen plenty of heavy rain.
The Sirius is built in the UK and comes with an impressive two-year warranty, but should you have any reliability issues Exposure is renowned for its customer service.
In conclusion, the Sirius Mk4 is an excellent little light for a range of applications. It excels in towns and cities, with that bright pulse setting making you seen when filtering through traffic, and the sheer number of modes means you can set it up exactly how you want it.
At just 79g and 100mm long it's easy to keep in a rear pocket or rucksack as a backup to your main light, and thanks to its brightness it'll get you out of any dark trouble you find yourself in.
Compared with some lights on the market the £99.95 price tag might seem steep, but you really are paying for what you get here: the solid body and technology all backed up by top notch customer services should things ever go wrong.
My own Mk1 is a fair few years old now and has never failed me, and still puts out the same burn times as it did when new.
A worthwhile investment for the year-round commuter and occasional night time trainer
If you're thinking of buying this product using a cashback deal why not use the road.cc Top Cashback page and get some top cashback while helping to support your favourite independent cycling website
road.cc test report
Make and model: Exposure Sirius Mk4 front light
Size tested: n/a
Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
Exposure says: "The Sirius is built to excel in urban environments. With a 500 lumen output, suitable for off-road riding and side illumination it rules the road. The Sirius will keep you safe and seen for miles with; constant and pulsing modes, long battery life, USB charging and OMS for adapting burntimes. Every Sirius is hand built and individually tested in the UK."
It certainly is a clever little light that is capable of many tasks.
Tell us some more about the technical aspects of the product?
- Smart Port Technology +
- Cable Free Design
- Intelligent Thermal Management
- Optimum Mode Selector
- Fuel Gauge
- Hand Made in the UK
In the box: Sirius MK4, QR handlbar bracket, USB charge cable, Quick start guide
Exposure lights are really well put together – solid engineering.
Excellent for urban applications but can cope with much more.
No flimsy complex brackets or weak buttons in sight. It's been dropped and soaked many times with no issues.
Barely noticeable on the bike or in a rear pocket for emergencies.
You get what you pay for. I don't think you are getting a bad deal considering the quality of the light.
Tell us how the product performed overall when used for its designed purpose
Brilliant as a commuter light or backup to your main.
Tell us what you particularly liked about the product
The range of modes.
Tell us what you particularly disliked about the product
The bracket can sometimes move through vibration.
Did you enjoy using the product? Yes
Would you consider buying the product? Yes
Would you recommend the product to a friend? Yes
Use this box to explain your score
The Sirius Mk4 is a cracking little light that does everything it is designed to do well. As a commuter light, the range of options and that pulse setting are perfect, offering decent burn times and quick charging. The underlying fact is that you are paying for the quality and the design; you always know it's going to turn on and get you home regardless of weather conditions.
About the tester
I usually ride: Kinesis T2 My best bike is: Mason Definition
I've been riding for: 10-20 years I ride: Every day I would class myself as: Expert
I regularly do the following types of riding: time trialling, commuting, club rides, sportives, fixed/singlespeed
With 20 years of road cycling and over 150,000 miles in his legs it's safe to say Stu is happiest when on the bike whatever the weather. Since writing his first review for road.cc back in 2009 he has also had a career in engineering including 3D-CAD design and product development, so has a real passion for all of the latest technology coming through in the industry but is also a sucker for a classic steel frame, skinny tyres, rim brakes and a damn good paintjob.
His fascination with gravel bikes is getting out of control too!