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What is “Feu” ?


“Feu” is a space brightness index that quantifiers the human sense of brightness. In other words, it assigns a numerical value to brightness as perceived by the human eye. Using “Feu,” it is possible to execute lighting design more objectively and quantitatively, rather than relying solely on the perceptions of the designer. In spaces where indirect or architectural lighting is utilized, a lighting designer can plan the overall environment so that it appears bright to the eye, without excessively raising the average illuminance at floor level.
“Feu” makes it possible to express, in concrete terms, the “human sense of space brightness,” which cannot be achieved with “illuminance,” the conventional index of brightness. It is a new approach that promises to facilitate both energy conservation and the design of pleasant, comfortable light environments.

Feu : 16.8

The “Feu” for this space, visualized as a building lobby, is 16.8. The atmosphere is open. LED base lights are capable of illuminating the ceiling as well, and generate higher brightness than conventional base lights.

  • Image
  • LED Base Light
    FYY26677C LT9
    FYY26681C LT9

1 “Feu” makes it possible to express human sense of brightness in numerical terms.

If you compare the two spaces shown, Space A appears to be brighter. However, the average illuminance of floor in Space A is 120 lx, while that of Space B is 190 lx, meaning that when measuring illuminance (brightness of a planar surface, in this case the floor), Space B is actually brighter. When using “Feu,” however, the brightness of Space A is Feu10 while that of Space B is Feu6, clearly and numerically expressing the greater brightness of Space A.

  • Space A
  • Space B

2 “Feu” can be utilized for energy-efficient, pleasant lighting plans.

If you compare the two spaces shown, Space A appears to be brighter. However, Space A contains only four lighting fixtures, while Space B has five, meaning A consumes less energy. With “Feu” it is possible to predict the overall brightness of the space, including walls and ceiling, which could not be done by quantifying average illuminance of floor, and facilitates energyefficient lighting plans.

  • Space A
  • Space B

3 Precisely targeted lighting design is possible with combined use of “Feu” and “lx” values.

Combined use of the units “lx,” which measures illuminance, and “Feu,” which gauges overall brightness, enables lighting design precisely targeted to create specific atmospheres such as “soft,” “open,” “calm,” etc.

  • Simulation A
  • Simulation B
  • Simulation C
  • Feu value benchmarks for each area