Gemini's Iris rear light claims to pump out a retina-melting 180 lumens of red. That's enough to get you seen in any conditions, and there are plenty of lower-power modes for general riding too. And it's well made.
First things first: ye gods, this thing is bright. You know when you turn a light on, and you think, "MY EYES!"? Well I did that with the Iris, only to find out it wasn't even on the brightest setting.
In fact, it wasn't even on the second-brightest setting. Seriously, this is one bright rear light. I think I can safely say it's the brightest rear light I've ever fitted to my bike. It's positively nuclear on its top power. I haven't ever used that setting out on the road, for a couple of reasons. Firstly, I've been using the light at night, when it's more light than I think I'd ever need, unless I was venturing out onto a trunk road or something. Secondly, you'll suck the battery dry in about an hour.
So why even have it, then? Well, if I were to head out to an evening time trial in the summer on a fast (read: busy) course, it's exactly the kind of light output I'd want. You can probably see it from a mile away in broad daylight. And for a 10, or even a 25, it'll go the distance. Assuming your 25 goes well...
There's more to the Iris than full nuclear, though. It has two different flash settings, and five different power levels, and you can program the light to use the power levels you want. You get to choose from 10, 30, 50, 100 and 180 lumens. For most riding I found the 10-lumen setting to be more than adequate, and you get the best part of a day of light on pulse mode (the more-off-than-on flash setting). For daytime running, 50 lumens in pulse mode gives you 8hrs of run time and left me thinking that I'd get seen even on quick roads. The brighter settings, and the more intense flash mode, mean shorter run times that might not last a club run.
Talking of club runs, I expect you're wondering if there's a group-friendly constant option... The answer, if you were to read the instructions, or go to the Gemini website, is no: there's no mention of one. But it is there, hidden away. Press the power button for six seconds and you can cycle through the power levels on constant. Mostly I used that for chaingangs and rides with friends, and the 10-lumen low-power level was good for more than 8 hours, with higher power knocking down the battery life considerably. The power button serves as a visual indicator of the power level, giving you a decent warning that the lights are going to go out.
Mounting is simple enough. There's a seatpost mount (really only suitable for a round section post) and the light fixes on with a chunky silicone O-ring. The light tends to point down a bit, but that's pretty good because it lights up the rear tyre and the road behind you, and doesn't point directly into the eyes of anyone behind you, which they wouldn't thank you for. There's a clip for bag-mounting too.
Charging is via a Micro-USB socket and the 900mAh Li-Ion battery takes a couple of hours to fill back up. The port is covered by a rubber flap that needs a bit of attention to make sure that it's snugly fitted, but I've not had it pop off during a ride and the light has seen some pretty dismal conditions with no water getting inside.
It's a nicely made light: the aluminium body gives it a quality feel, and it's survived a few knocks with only the odd scratch. The downside to the recessed lens is that it can collect mud on mucky lane rides, and the Iris doesn't have the kind of side visibility that you get from a rear light with a translucent body, so it's not quite as obvious around town as something like a Cateye Rapid X.
Although £60 is a lot for a rear light, if you're looking for one that will offer top-class long-range visibility on fast roads, and in daylight, this should be near the top of your list. If you're going to use the Iris as more of an all-rounder then lower modes preserve the battery life and they're more than enough light for nearly anything. The lack of side visibility marks the Iris down in the overall safety stakes, but the build quality means it's a light that should last. Overall, it puts in a very good performance and it's a light I've been happy using as a single rear for all kinds of riding.
Top-of-the-class brightness for when you really need to get seen, with a good range of lower power options
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road.cc test report
Make and model: Gemini Iris Rear Light
Size tested: 180 Lumens, Four Modes
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?
Be Visible with 180 Lumens.
With 180 lumens, the incredibly small, yet powerful, Gemini IRIS LED Rear Light will let other road users know exactly where you are, allowing you to ride your bike with confidence.
Seat Post and Clip Mounts Included.
Use the seat post mount with o-ring attachment to quickly mount the Gemini IRIS to your bike, or opt for the clip mount to secure it to your backpack.
Built-In USB Rechargeable Lithium Ion Battery.
The Gemini IRIS is powered by a high capacity lithium ion battery. A quick 90 minutes of charging through a USB port will get you up and going again with a full battery.
12-Hour Runtime with a Smart Battery Indicator.
Designed as a high performance safety light, the Gemini IRIS will last a full 12-hours of continuous usage. Ride through your nightly commute comfortably, and when it's time to charge, the indicator will let you know.
User Programmable Brightness Levels.
To give you ultimate control, we've designed the Gemini IRIS to be user programmable and given you four flash modes to play with. For each mode, you can choose your preferred brightness with adjustable levels of 10, 30, 50, 100 and 180 lumens.
Tell us some more about the technical aspects of the light?
Brightness 180 Lumens
Battery and Runtime 900mAh Lithium Ion Battery.
Built-In Battery Level Indicator.
Four Modes Low Flash, High Flash.
Low Pulse, High Pulse.
Adjustable brightness levels 10-180 lumens.
Material Hard Anodized Aluminum
Safety Low Battery Warning and Battery Overcharge Protection.
In the Box IRIS Rear Light
USB Charging Cable
Seat Post Mount and Clip Mount
It's easy once you've found out how to switch between flashing and steady.
Simple silicone O-ring, no angle adjustment.
Put up with plenty of abuse with no problems.
Not great in super-high-power modes but good on the ones you use most.
Overall performance really good: lower settings great for everyday use with nuclear options for daytime and big roads. Side visibility not as good as some.
Feels like a solid unit.
Not exactly heavy.
Good value for what you get.
Tell us how the light performed overall when used for its designed purpose
Tell us what you particularly liked about the light
Good range of brightnesses, well made.
Tell us what you particularly disliked about the light
'Secret' steady mode, battery life in high beam, side visibility.
Did you enjoy using the light? Yes
Would you consider buying the light? Yes, especially if I was an A-road rider.
Would you recommend the light to a friend? Yes
Use this box to explain your score
If you want bright and well made, this is definitely that. If you're looking for something for long-range visibility in the daytime, then it's an excellent choice. As an all-rounder it gets marked down a bit for battery life and side visibility.
About the tester
I usually ride: whatever I'm testing... My best bike is: Kinesis Tripster ATR, Kinesis Aithein
I've been riding for: Over 20 years I ride: Every day I would class myself as: Experienced
I regularly do the following types of riding: road racing, time trialling, cyclo-cross, commuting, club rides, sportives, general fitness riding, fixed/singlespeed, mountain biking, Mountain Bike Bog Snorkelling, track
Dave is a founding father of road.cc, having previously worked on Cycling Plus and What Mountain Bike magazines back in the day. He also writes about e-bikes for our sister publication ebiketips. He's won three mountain bike bog snorkelling World Championships, and races at the back of the third cats.