There seem to be 2 versions of the VIKA, one that takes two CR123A rechargeable 3.6V batteries, and another that takes one 18650 battery. My guess would be that the 18650 version would be less bright because of the lower voltage than two CR123As, but that is supposition on my part. In response to a question posted on the FifthUnit website asking about the relative brightness of the GLIMT and VIKA flashlights, Kai of FifthUnit posted this reply:
Hello:
The VIKA with 2xCR123A has lower light output relatively to GLIMT. VIKA 2xCR123A gives about 62 lumens (76 lumens for GLIMT) but a stronger beam center (61.16 relative lux). However the VIKA burns hot after 5-10 minutes of usage. I get about 30 minutes of light from VIKA. I haven't try the GLIMT yet regarding beam duration.
Kai