Deciding which instrument to use obviously depends to a large extent on what is available - meaning another exercise in listing priorities. For 'FOH' (front of house) throws of any distance in the auditorium, profiles are essential, both to avoid undesirable lighting up of the auditorium from scatter light, and to allow sufficiently precise control of the beam to prevent spillage on to the proscenium. However in a small hall there is a lot of merit in considering fresnels or PCs (well barndoored) at close range when a lot of spread is possible from a few lamps. For onstage use, Fresnels and PCs come into their own with fast-to-set soft edges - profiles are the most versatile instruments but they inevitably take longer to focus. For backlight, fresnels and beamlights are favourite, while floods are to be thought of only for wide expanses of scenery. (Use for actor light only in situations of extreme desperation). For theatre-in-the-round, barndoored fresnels give the required smoothness and spread. Existing installations in most theatres and halls are likely to be based on fresnels and profiles: anyone buying new equipment should look seriously at including a goodly proportion of the new generation PCs giving smooth soft-edge beams without stray scatter light and at the versatility of the variable beam profiles.
Example plan for a play
This plan shows instruments being allocated to our play in a very orthodox way: profiles for the front-of-house and fresnels for onstage. If a couple of PCs were available, they would be a useful alternative on the ends of the stage spot bar: this is a position where any scatter light shows up badly on the side walls of the set. Whether 500 or 1000W units are required will depend mainly on length of throw, perhaps with the changeover around 6 to 8 metres. However, it is important always to remember that the actual level of light intensity is not so important as the BALANCE.
Example plan for 'in the round'
Fresnels have been allocated everywhere because they have a good smooth spread (profile edges can be very difficult in small theatres in the round). Every spot must have a barndoor to contain spill from the audience eyes. Each become a pair of spots since this is the only way that it is possible to light fully to the sides of the acting area. Too many-spots? Then perhaps just one cover in a neutral shade (thereby halving the number on the plan) and utilising a couple of pairs of straight downlighters to add colour toning in warm or cool.
Example plan for a musical
The actor face lights are profiles from the front and fresnels onstage, with the second bar being less powerful units - face light is rarely important upstage in a musical. The backlights are fresnels, although parcans would be nice if available. For the sidelighting, profiles have been used downstage to contain the light in a tight corridor across the front - often advisable when front cloths or running tabs are in use. Midstage sidelighting use fresnels for a good spread, while the optional upstage sidelight again uses profiles to keep the light clear of the skycloth.