Lumen can mean:
- Lumen (unit), the SI unit of luminous flux
- Lumen (anatomy), the cavity or channel within a tubular structure
- Thylakoid lumen, the inner membrane space of the chloroplast
- Phenobarbital (trade name)
- 141 Lumen, an asteroid discovered by the French astronomer Paul Henry in 1875
- Lumen (band), Russian alternative rock band
- Lumen Pierce, a fictional character played by Julia Stiles from the television series Dexter
- Lumen (branding agency), a design and branding company headquartered in Milan, Italy
- USS Lumen (AKA-30), a US Navy ship