What are Lumen levels?
Lumen levels play a crucial role in enhancing our health objectives by training our body’s metabolic flexibility. Using a Lumen device throughout the day helps you gain significant insights into your metabolic flexibility.
Lumen levels offer insights into your present metabolic condition, categorized across 5 levels indicating fat, carb, or mixed energy usage. These levels can be interpreted thus:
- Levels 1 or 2: Primarily using fats for energy.
- Level 3: Balanced use of fats and carbs.
- Levels 4 or 5: Mainly burning carbs for energy.
Or in more detail:
- Level 1: Over 84% fat energy.
- Level 2: 63%-84% fat energy.
- Level 3: 42%-63% fat energy.
- Level 4: 60%-80% carb energy.
- Level 5: Over 80% carb energy.
Variations in Lumen Levels during the day signify changes to metabolic flexibility. Ideally, mornings show low levels, indicating overnight fat burning. Any high-carb meal will lead to elevated carb-burning levels and lower fat-burning levels. It’s MUCH easier for your body to get energy from its limited carb stores rather than from your effectively unlimited fat stores.

Lumen’s bar widget displays your current level, along with the percentage of fat and carb burned, based on CO2 data.
There are no optimal timings for high and low Lumen levels which will naturally vary throughout the day depending on your diet and activity levels. However, you should broadly expect to see this:
Last Updated on 26 January 2026 by the5krunner

tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors.

