The mechanical and
optical system
of the fresnel luminaire is similar to that of the PC, i.e. a
lens
and a spherical reflector, except that the
lens
is a fresnel lens.
Fresnel
lenses are moulded and have a diffusing
pattern
on the plane side of the
lens
which diffuses the inherent ring
pattern
of the fresnel lens. Sometimes a diffusing
pattern
of parallel lines is used in order to distort the round shape of the
beam
into an elliptic shape, which is useful when the
lighting angle
is shallow.
A fresnel luminaire is shorter than a PC luminaire as its
lens
has a shorter focal length, and the
lamp
and
reflector
travel a shorter distance. Accessories such as barndoors, flags and top hats can be inserted in the color frame groove in front of to the
lens
to
cut
off unwanted spill and ambient light.
The fresnel is designed for short throws where a wide
beam
angle is required. The short focus fresnel
lens
produces a typical wide, intense and soft light
beam
. Fresnels
throw
a substantial amount of indirect light, or spill, over a large area surrounding the luminaire.
The fresnel is an essential tool of
stage
lighting. The fresnel
lens
is relatively inexpensive and simple to manufacture, hence fresnels are affordable even on the humblest budget.
Fresnel
luminaires are most often used for short throws, where a wide
beam
angle is required, and a short focus fresnel
lens
can replace the plano-convex
lens
with better effect.
The soft and diffused light of a fresnel Note that the merging are not clearly define.
Fresnels are available in various sizes and wattages. Typically,
beam
angles vary from 16O to 60O .The
light distribution
pattern varies, depending on the
beam
angle. A wide angle setting (flood) will produce an even flat field of light with a soft, undefined edge. A narrow angle setting (spot) will produce a distinct light
pattern
with the light concentrated to a
hot spot
in the center of a wider scatter of light.
Fresnels are typically hung above the actor, or are used for backlight. The
soft edge
quality makes the
fresnel useful for blending acting area lighting, especially when backed by scenery on which the
clear
cut of a PC
beam
would be glaringly obvious. Fresnels are almost never placed front of house since the
indirect light
would illuminate the audience, and they can severely obstruct effects such as projections
A fresnel luminaire with a 650 watt
lamp
with a 150 mm lens, or 1000
watt
fresnel with a 200 mm lens, hung on any of the on-stage lighting position, will adequately illuminate an actor on a small stage. On larger stages, where a longer
throw
is needed, fresnels with lamps of 2000, 2500 and 5000 watts with lenses in the range of 250 - 300 mm, are used.
Fresnels are an essential luminaire in film and television lighting, where large areas must be lit from a close range. A wide range of fresnels is available, customized for the needs of television and film lighting.
Fresnels with high wattage
HMI
lamps (1,200-12,000 W), are basic film lighting equipment due, among other things, to the high
color temperature
of the discharge lamp. On occasion
HMI
fresnels are used for special
lighting effects
in the theatre when extremely powerful light is required. Since these
HMI
lamps cannot be dimmed by theatre dimmers, a
mechanical dimmer
must be used.
