TEC 36
deltalight.com
30°
30°
20°
Beam angle: 40°
20°
45°
45°
60°
60°
75°
75°
90°
90°
105°
105°
800
1200
1600
Field angle: 60°
C0
C90
30°
30°
45°
45°
60°
60°
75°
75°
90°
90°
105°
105°
200
400
500
I ( cd/klm )
Apart from the lumen output and the power it consumes, a luminaire is characterized by its
luminous distribution. At Delta Light® we have the knowledge and infrastructure in-house to
determine those characteristics of the luminous distribution.
Polar diagram
The luminous distribution of a luminaire is shown in a polar diagram, which is a two-
dimensional representation of a three-dimensional measurement of the luminaire by the
photogoniometer. The curve on this diagram tells us the direction whereto the light is
being emitted, together with the luminous intensity of the light in the different directions, in
function of the viewing angle in different planes. The C0-plane is represented by a full line
and indicates the luminous distribution of the luminaire, perpendicular to the light source’s
longitudinal axis. In case of round or square shaped luminaires where no longitudinal axis
can be determined, the C0-plane indicates the main direction of the light being emitted
The C90-plane is represented by a dashed line and indicates the light distribution along the
longitudinal axis. On the diagram each circle represents a value of the light intensity and is
expressed in candela per kilolumen (cd/klm). The circles are divided in angles that indicate
the direction of the light intensity.
As an example we have the polar diagram
of the Sneak-R on the left. The C0-plane
shows that almost all of the light is emitted
forward and only a small amount of light is
emitted backwards (full curve lies between
-15° and 90° in the C0-plane). As the
curve does not exceed the 90° line, it
means that no light is emitted upwards.
The peak of the curve is around 15° and
shows a value of over
500 cd/klm. On the C90-plane we see a
symmetrical curve between -35° and 35°
with a peak at 0° and a value of 300 cd/
klm.
Up-to-date photometrics of the luminaires
mentioned in this Lighting Bible® are
available on the website. Photometrics on
the new luminaires will be available in the
upcoming months.
Beam angle
Important to know is how ‘beam angle’
exactly is defined? It is the degree of
width of the light that is emitted by a
light source and it is determined by the
angle between the 2 points on an axis
where the intensity of the light drops
down to 50% of the maximum light
intensity (Imax) of the light source.
This 50% of Imax determines from
which point the light fades and from
where the human eye will consider the
light as being spill light. The human eye
will particularly see the inner circle as
highlight, also known as the half value
angle or beam angle, whereas the
outer circle is known as the field angle.
The example on the right has an Imax
of 2000 cd/klm.
By taking half of this value (1000 cd/
klm) and intersecting the curve, we
can determine the beam angle, which
is 40°. The outer lines of the curves
determine the field angle, which is in
this case 60°.
PHOTOMETRICS
