What could be better than the Cateye Volt400 Brompton Light? We think a Cateye AMPP 500, 800 & 1100! The AMPPs are brighter, have better side visibility and have an equally integrated fit on your Brommie.
Yes, we have loved the Volt400 Brompton front light, but at Perennial Cycle we recommend 500 Lumen as the minimum brightness for night riding. 500 Lumen is a good level of brightness for being seen. If you will be relying on the light to shine a path with minimal streetlights, we'd recommend the 800 & 1100 so that you SEE the potholes before you ride through them.
Perennial Cycle is an urban shop in Minneapolis with a lot of commuting cyclists as well as a lot of potholes. This gives us a lot of expertise at setting up lights for cyclists. Our expertise with brackets and unique setups had us thinking we could likely come up with some rechargeable light solutions that would be brighter that the Volt400 Brompton front light, yet be just as clean and unobtrusive a fit to our beloved Brompton Folding Bikes. After setting up a few of these for customers, we decided to make it available for more than our in-house customers.

All 3 models of the AMPP for Brompton fit under a front bag & none interfere with the fold

Specs for the AMPP Lights for Brompton:

AMPP500: 500 Lumen: 1.5hrs/high, 250 Lumen: 3hrs/low, 50hrs/flash mode (33mm wide x 25mm tall x 100mm long)
AMPP800: 800 Lumen: 1.5hrs/high, 200 Lumen: 4hrs/low, 30hrs/flash mode (32mm wide x 24mm tall x 102mm long)
AMPP1100: 1100 Lumen: 1.5hrs/high, 400 Lumen: 4.5hrs/low, 50hrs/flash mode (48mm wide x 26mm tall x 135mm long)

The Cateye AMPP lights make a great choice for Brompton Folding Bikes because of their compactness. No worries about interfering with your front bag. Also, all 3 versions have excellent side visibility and offer a variety of light modes. If your daily use is less than 1-1/2 hours you can run on high beam, but if you need to squeeze the most out of the light, blink mode will get you an impressive 30 or 50 hours.

Extra:

If you are using a Brompton saddle (either width), you should consider the Rapid Mini rear blinky light for Bromptons. It mounts very cleanly onto your saddle. We recommend having this on your bike, no matter what other lights you are using.

Rapid Mini Saddle Light for Brompton
We recommend the Rapid Mini Saddle light as it is a simple way to make yourself more visible out on the roads (always a good idea).