The Moon Arcturus Auto is a super little rear light for commuting and general riding. It's useful for a variety of scenarios, with seven modes in total – two main modes each with three sub-settings, plus a daytime mode for added safety. The single button is perfect for on-the-move adjustment.
My commute isn't lit, and includes a mix of A roads and narrow country lanes. The Moon's 35-lumen modes are easily bright enough for pitch black riding, while the extra-bright 70-lumen double flash is great for daytime. This is enhanced by the Auto Mode (hence the name), which switches the light on when it senses very low light. This came in really handy when going from sunshine into heavy tree cover, giving that bit of extra safety against drivers adjusting to the light change.
The Arcturus Auto is simple to set up, with a small bracket and just one securing band. I took it out of the box before I left for work one morning and had it on the bike and flashing in under two minutes.
It attaches to your bike via an RB-22 bracket which, helpfully, is compatible with all of Moon's other lights, making switching out lights for different situations a breeze. The Arcturus also comes with two O rings: the RS-G for 20-35mm diameters, the RS-H for 35-52mm diameters, giving a wide range of places to mount the light.
With its CNC aluminium heat sink casing and one-button operation, turning the light on while moving is very easy. Some lights have a tiny button, resulting in much under-crotch investigation, but the large button right in the centre of the Arcturus is easy to find.
The Arcturus Auto gives a spot angle of 105 degrees, which equates to a 26-metre-wide beam when 10 metres behind the light. The total angle of 270 degrees means the light can be seen by those only marginally behind you.
Its rechargeable lithium polymer battery gives a run time of between 1:20 and 17 hours, depending on the setting. As with any light, the flashing modes retain more battery life than constant ones; constant at 35 lumens will drain the battery in 1:20, whereas 35 lumens flashing will go for 8 hours. With its USB rechargeable feature, this shouldn't cause any problems, but it is worth considering the run time of each mode; I am able to charge the light at work, but this isn't an option for everyone.
Wet commutes shouldn't have any adverse effects – I've been testing the light in relatively dry conditions, so had to simulate some heavy downpours with a hosepipe, and I can report that no water got in.
A sturdy, well-made rear light with ample settings for day and night
road.cc test report
Make and model: Moon Arcturus Auto
Size tested: n/a
Tell us what the light 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?
A USB rechargeable light that is suitable for commuting and training.
270° total angle
105° spot angle
Tell us some more about the technical aspects of the light?
pc (30 chips) Rectangular ring COB high brightness red LED
*CNC Aluminium heat sink casing
*Light sensitive auto ON/OFF
*Auto safe mode
*Mode memory function
*Rechargeable lithium polymer battery (3.7V 300 mAh)
*7 modes: Mode1 / Mode2 / Mode3 /FL1/FL2/FL3/DAYFLASH(DOUBLEBLAST)
*Quick release universal bracket RB-22 (fits all round bars and AERO style bars)
*Low battery, charging and fully charged indicator
*Automatic fully charged cut-off system
*Water resistant (IPX 4)
The CNC aluminium heat sink casing gives the feel of a very expensive light. It also feels wonderfully robust.
One big button means on-the-move turning on is easy. Using big gloves is no hassle, with a positive click for each setting.
The O rings are easy to pop on and off but still feel secure on the bike. The universal bracket will also be welcome if you plan on switching out different Moon lights.
After drowning it with a hose there were no problems or any sign or water ingress.
Compared to its competitors, it does quite well but some settings drain the battery alarmingly quickly for those with a long commute or training ride. Two-hour charge time from flat.
Large range of flashes and brightnesses means it has a setting for every occasion. The day flash is super-bright.
You won't notice it, unless you're racing a hill climb, then take it off.
Tell us how the light performed overall when used for its designed purpose
Super-bright on misty mornings, with ample settings. Easy to charge at work.
Tell us what you particularly liked about the light
The single button meant I could quickly turn it on, even when I'd forgotten and had to do it while riding. The memory function that remembers your last setting is also very useful.
Tell us what you particularly disliked about the light
Battery time could be a little longer but that's a sacrifice of the super-bright modes.
Did you enjoy using the light? Yes
Would you consider buying the light? Yes
Would you recommend the light to a friend? Yes
Use this box to explain your score
A super useful light for the approaching winter. It's easy to use and sturdy in both design and attachment.
About the tester
I usually ride: Rose Xeon RS My best bike is:
I've been riding for: 5-10 years I ride: Every day I would class myself as: Expert
I regularly do the following types of riding: road racing, time trialling, cyclo-cross, commuting, club rides, general fitness riding, I specialise in the Cafe Ride!
Son of a Marathon runner, Nephew of a National 24hr Champion, the racing genetics have completely passed him by. Liam spends his time plodding his way through cyclocross races, very busy not winning. As an advocate for perfectly clean chains, he can be found cleaning his bike instead of training. A shop mechanic, Liam has many helpful skills, such as being able to identify 'cross tubs by the tread pattern alone. If you bump into him, he'll probably be eating.