AIEL MARKET
Purchase Guide

Stage Lighting Fixtures

This is a short article regarding the choice of
stage lighting luminaires. It is a general guide
and will not compare one brand to another,
but will instead discuss the three most
common light types and their typical uses.

THE FOLLOWING MAY NOT BE REPRODUCED
WITHOUT PERMISSION FROM THE AUTHOR ©

Topics

General

Deciding upon what light to buy is based on its intended purpose,
light output and coverage, beam quality, power consumption, fixture
size and weight, and price. Because what follows will be without
regard to total costs, you will have to modify your final purchase
to fit your budget. Here are suggestions regarding the other criteria.

Purpose

    While any fixture could be used for almost any stage lighting purpose, some are better suited than others. Basic uses are:

Wash:               Fresnel, PAR, Ellipsoidal
Spot:               Ellipsoidal, PAR
Special Purpose:    Ellipsoidal, PAR

Light Output

    This will be partially limited by available dimmer capacities and total line power. However, for now, concentrate just on the amount of light required and the area to be lit. 500 watts is considered the minimum for professional stage purposes, but can be lower depending on the exact purpose, distance from what is to be lit and how much area is to be illuminated. Generally, larger stages and the use of dark colours will mean a higher light output requirement or more fixtures of a lower output. This can be achieved by using high-output lamps for a given wattage, higher-wattage lamps, more fixtures, wider-angle beam spread, or some combination of these.

    Light output of a fixture itself depends on lamp wattage and filament design, reflector size and design, and lens size and design. Rather than teaching a long lesson on these criteria here, one may simply peruse the specification tables provided by the fixture manufacturers to compare one to a series of others. You may need to ask an experienced person what light levels might be required for a given purpose. Otherwise, try to experiment with sample fixtures before purchasing. Some companies will rent to you and then subtract some portion of the rental price from the purchase price if you buy within a specified time. Enquire from your chosen suppliers to see who offers the best deal.

Beam Coverage

    Coverage is determined by lens system's focal length. The wider the angle, the greater the coverage. Fresnel and ellipsoidal usable beams typically range from 10 to 75 degrees, depending on model and fixture design. For PAR fixtures, the lamp installed determines beam angle along with the fixture's barrel length. All but the most narrow PAR lamps have stippling or multiple lenses on their bulb surface to determine its beam width. Each scatters or bends the light by a predetermined amount.

    Using the 1000-watt `FF' series of lamps as examples, the stippled surface of the Narrow Spot acts as more of a diffuser which expands the beam angle as compared to the clear lens of the Very Narrow Spot. The Medium and Wide Floods have rows of small lenses on the bulb surface. The high output Medium Flood lamps (designated: FFR) have eight rows, while the Wide Flood (FFS) ones have twelve. With more rows on the latter, its individual lenses cause the beam to spread much more.

    Smaller PAR lamps behave in similar ways. Again, peruse the manufacturers' literature for beam and field angles to determine the ones suitable for your purposes. Most users have a selection of lamps available so as to make their PAR fixtures more versatile.

    In addition, realise that the PAR 38 fixtures can also use `R' lamps. These give a softer and typically much wider beam than the PAR 38 lamps. Users should also realise that there are inserts for some PAR fixtures that have a reflector and quartz lamps available. Some of these work well, while others do not. Try before buy!

Beam Quality

    Each fixture type has a different beam characteristic. Fresnels and PARs tend to be soft edged, while ellipsoidals are hard edged, although the latter may be defocused to achieve a softer-edged beam. The reason for this is the lens. Fresnels and PARs tend to have diffuse lenses, while ellipsoidals typically have plano lenses.

    There are exceptions: Very Narrow PARs (VNSP) have a fairly hard edge, although due to their design, they have a halo around the beam from direct filament projection. Ellipsoidals with step lenses have a more diffused beam, yet in perfect focus, that beam pattern is still harder edged than a PAR lamp.

    Regardless, speaking in generalities, one would choose an ellipsoidal for a precise beam, a PAR for a less precise beam, and a fresnel for the least precise beam.

    Now, there are other reasons for choosing one fixture over another. Fresnels have variable focus capability over a wide range; PARs have a fixed beam of an oval pattern, but by choosing various lamps, one may achieve wider or narrower angles. PARs also tend to be powerful (put higher light levels on to a surface) for their wattage. In addition, fresnels can have an oval beam if one uses oval-projection lenses. Ellipsoidals have built-in shutters which feature the ability to shape the beam better than the other two examples. They can also project patterns (images) on to a surface.

Power Consumption

*   75 watts draws 0.63 amps
*   90 watts draws 0.75 amps 
*  100 watts draws 0.83 amps 
*  150 watts draws 1.25 amps 
*  250 watts draws 2.08 amps 
*  300 watts draws 2.50 amps 
*  500 watts draws 4.17 amps 
*  600 watts draws 5.00 amps 
*  750 watts draws 6.25 amps 
* 1000 watts draws 8.33 amps 

    Be aware that if in your area there is higher line voltage, lamps will draw more current. Also realise that when dimming an incandescent lamp, the current draw will not be linear. That is, applying half voltage does not mean a draw of half current. This is because varying the voltage results in different filament temperatures which cause that filament to vary in resistance. This is not linear in nature, so neither is the current draw - and for that matter, neither is light output. So half voltage does not mean half intensity either. Even if it did, the eye/brain would not perceive it that way.

    In reality, half light output typically occurs at about 98 volts. At that voltage, power consumed will be about 73% of that at 120 volts. So for this example, at 82% voltage, wattage is 73% and light output is 50% - hardly linear.

Size and Weight

    If you have a low ceiling, or little pipe or truss space or weight capacity, you will have to limit the size of the fixtures chosen. If you are touring, total weight must be considered. The latter will determine truck tonnage and that is a factor at highway scales. Don't forget to include accessories such as pipe clamps and barndoors in both the size and weight calculations.

Summary Tables

The tables below list the stage lighting fixtures discussed in the
above article, along with their typical size and wattage designations.
The usual locations where they are used are also given. Be aware that
some other models, sizes and wattages are available for these fixtures.

LED Fixtures

This Article is
Available in
Plain Text for
Your Archives

Fixtures Guide, Text Format