This is the simplest type of lantern, consisting of a lamp and a reflector in a box, with no lens. The reflector concentrates the light towards the opening in the box. There is no control over the focussing of a flood, other than its general direction. Some floods have an asymmetric / directional reflector and are designed to light cycloramas. Older type symmetrical floods use standard ES (Edison Screw) or GES (Giant Edison Screw) filament lamps. The newer asymmetrical reflector floods (often called Cyc Floods) use linear lamps (to ensure an even cover across the reflector).

Symmetrical reflector

Asymmetrical reflector

The Fresnel (pronounced "Frennel") is a soft-edged spotlight with more control over beam angle than floods, but less control than profiles.
The lens is a series of stepped concentric circles on the front and pebbled on the back and is named after its French inventor, Augustin-Jean Fresnel (1788-1827). He developed the lens for French lighthouses so that they could be seen further out to sea and could achieve a longer focal length with a lot less glass than a standard plano-convex lens. It was first used in stage lighting in the late 1920s.
The size of the beam can be adjusted by moving the lamp and reflector closer to or farther from the lens, either by a screw mechanism or a simple slide. The beam can be shaped by the four barndoors attached to the front of the lantern.

Fresnel "spotted down"

Fresnel "flooded"

The PC is common in Europe, but is rarely seen in the US. The basic design of this lantern dates back to the first days of stage lighting, but the modern version has one important difference. This lantern uses a modified plano-convex lens with a pebbled effect on the plano (flat) side. The pebbled effect gives the beam its characteristic soft edge. The edge of the beam is slightly harder than a Fresnel, but is not hard edged. The pebble convex lens uses the efficiency of the plano convex lens and gives the light a softer edge. Like a Fresnel, there is one focussing knob to change the beam angle.

PC "spotted down"

PC "flooded"

Profile lanterns produce clearly defined spots of light and are the most focussable and versatile of the lanterns. They have a lens (some have two lenses), a lamp and a reflector, and they also have shutters and a gate.
Profiles get their name from their ability to project the shape of anything placed in the gate of the lantern between the lamp and the lens. These shapes may be formed by the shutters, or they may be cut out of thin metal (a "gobo" - see diagram right).
Some profiles with only one lens have two sets of shutters, one of which gives a hard edge to the beam, and one which gives a softer edge. These are known as bifocal profiles.
Profiles with two lenses (zoom profiles) are best for projecting gobos and other shapes, as the size and sharpness of the beam is fully adjustable throughout the beam angle range of the lantern.
A zoom profile lantern is known by the range of its beam angle (e.g. Prelude 16/30, Cantata 18/32 are both zoom profiles from Strand Lighting's range).

A Leko is an ellipsoidal profile spot. Leko's are much more common in the US than the Zoom Profiles we tend to prefer in the UK. They are of fixed beam angle. The name Leko is a contraction of the original manufacturer's names (Joseph Levy and Edward F. Kook - founders of Century Lighting). Leko's were originally patented in 1933, and is still manufactured today by Strand Lighting (which now owns Century Lighting).
Ellipsoidal profile spots are sometimes known as ERS (Ellipsoidal Reflector Spots).

A followspot is a special type of profile lantern with addional controls, extra handles, sights, built-in colour changer and iris, and is usually of much higher power.
Page about Super Trouper followspots

With the lenses far apart, the beam is narrow

With the lenses close together, the beam is wider.

This lantern first came into use in the 1970's in the Rock and Roll industry. It quickly found favour due to the relative cheapness of the lantern, the weight and the ease of focussing. The lantern itself is simply a "can" in which the PAR lamp is contained (hence "Parcan"). The PAR (Parabolic Aluminised Reflector) lamps are available in a range of beam angles (see table below), depending on the amount of diffusion on the front lens of the lamp. The lamp is a sealed beam unit consisting of a lamp, reflector and lens in one.
Because the light produced can be very intense, Parcans are especially suited to strong colours or for special effect. Be aware that deep colours can burn out quickly at full intensity.
The beam produced by a Parcan is an elliptical projection of the filament of the lamp, and this can sometimes be seen (as shadowed lines across the beam) in the Narrow lamps. The elliptical beam can be rotated simply by rotating the lamp. Access to the lamp is via the rear of the lantern.

PARCAN LAMP SIZES
The size of the parcan is given by a number which relates to the diameter of the lens in eighths of an inch. The most common is the Par64 1000W. Other sizes are the Par 16 (used in Birdies, and now superceded by the MR 16 dichroic lamp), Par 36, Par 38 (150W), Par 56 (300W). There are many variations of lens and wattage within a given size bracket.

PARCAN BEAM ANGLES (Par 64)
UK/Europe lamps are in blue, US lamps in red

Although the 240V lamps are most often used in the UK, 110V PAR lamps are often used in large UK venues or for touring due to the increased light output. Because the current is greater, the lower voltage lamps have smaller thicker filaments which give a more focussed beam than the thinner 240V filaments.

Standard parcan lamps have a GX16d cap.

OTHER BEAM ANGLES
PAR 16 (MR16 - birdies) - massive range of beam angles available
PAR 36 (pin spots) - beam angle around 5°
PAR 46
PAR 56