Marc Steinmetz Photography | The seven SI base units

ROBOT ACROBATS
The PTB’s unique robot-goniophoto-
meter measures light sources to be
used as transfer standards for cali-
bration of industrial applications. Its
three multi-jointed arms adjust the
light fixture – here an array of blue
LEDs – in space and orbit two photo-
detectors around it to measure its
luminous intensity and color in all
directions and at various distances.

[cd] ‘The CANDELA is the
luminous intensity, in a given
direction, of a source that emits
monochromatic radiation of
frequency 540 · 10¹² hertz and
that has a radiant intensity in
that direction of 1/683 watt per
steradian.’