Bril (unit)

The Bril derived from " Bril lance " is a psycho-physical unit for the perceived brightness of a light stimulus . It is defined as the brightness with which a surface with a luminance of 1 micro lambert is perceived by an eye adapted to the dark .

The perceived brightness is not proportional to the luminance of the examined test area. Instead it exists

• according to Fechner a logarithmic relationship (see Weber-Fechner law )
• a power law according to Stevens (see Stevens power function ).

The perceived brightness also depends on the state of adaptation of the eye, as it partially compensates for differences in the lighting level by adapting its sensitivity :

• an eye adapted to 100 microlambert perceives a luminance of 100 microlambert with a brightness of 3 Bril
• an eye adapted to 1 Lambert perceives a luminance of 0.01 Lambert = 10,000 microlambert also with a brightness of 3 Bril.

See also

• Sone : a psychoacoustic unit of measurement for the perceived loudness of a sound event
• Mel : a psychoacoustic unit of measure for the perceived pitch of sine tones

Remarks

1. ↑ (with for candela ) ${\displaystyle \mathrm {1\ \mu la={\frac {1}{\pi \cdot 100}}\ {\frac {cd}{m^{2}}}\approx 0{,}003\ {\frac {cd}{m^{2}}}} }$
   ${\displaystyle \mathrm {cd} }$

Individual evidence

1. ↑ JC Stevens, LE Marks: Stevens's Power Law in Vision: Exponents, Intercepts, and Thresholds. In: Fechner Day 99: Proceedings of the Fifteenth Annual Meeting of the International Society for Psychophysics . 1999, pp. 82–87 ( online ): "One bril is the brightness produced by 40 dB re 10 ⁻¹⁰ lambert [0.003 cd / m ² ] in a dark-adapted eye." (Ie the luminance causing 1 bril is around a factor of 10,000 (40 dB ) above the reference luminance 10 ⁻¹⁰ Lambert)
2. ^ G. van den Brink: Subjective Brightness during Dark-Adaptation. In: Vision Research. 2, No. 12, 1962, pp. 495–502, doi: 10.1016 / 0042-6989 (62) 90051-2 : “A bril is defined as the brightness seen by a dark-adapted observer when he views a luminance of 40 decibels (dB). "
3. ^ ^{A b} JC Stevens, LE Marks: Stevens's Power Law in Vision: Exponents, Intercepts, and Thresholds. In: Fechner Day 99: Proceedings of the Fifteenth Annual Meeting of the International Society for Psychophysics . 1999, pp. 82-87, Fig. 1 ( online ).