Lots more notes but here is some to start with:
LIGHT OUTPUT CALCULATIONS
a dinner candle provides about 12 lumens. A 60-watt Soft White
incandescent lamp provides 840 lumens.
Foot-candles =
candela / distance in feet * distance in feet
Foot-candles =
Lux / 10.764 = lumens/sq.
meter; 1fc=10.764lux
Foot-candles * 10.764 = lumens/sq.
meter =
lux
Lumens/sq. ft. * 1 = foot-candles; (1fc=1
lumen/ft²)
Lumens/sq. ft. * 10.764 = lumens/sq.
meter
Lumens * 0.07958 =
spherical candle
power
Lumens = Mean
Spherical Candlepower x 12.57
Luminous
Intensity (cd) = I = Luminous flux in solid angle ÷ solid angle℧(sr)
Lux * 0.0929 = foot-candles
Lux =
candela / distance in meters * distance in meters
Lambert * 0.3183 = candles/sq. cm
Lambert * 295.720 = candles sq. ft.
Lambert * 1 = lumens/sq. cm
Illuminance (lx) = E = Luminous flux falling on area (lm) ÷ Illuminated area (m²)
Illuminance (lx) = E = Luminous
intensity (cd) ÷ [distance in meters (m)]²
Luminance (cd/m²) = L = Luminous intensidy (cd) ÷ viewed luminous area (M²)
Luminous efficacy (lm/w) = h = Generated luminous flux (lm) ÷ Electrical
power consumed (w)
Efficacy=F(lu)/P(w)
F=Luminous Flux
P=Electrical
Power (wattage), in watts
LIGHT BEAM CALCULATIONS:
Beam diameter = distance * (2 * tan (
beam angle / 2))
Throw distance = Square root [(horizontal dist. * horizontal dist.) + (vertical dist. * vertical dist.)]
Inverse Square Law: E(fc)=I(cd)/D²(ft)² E(fc)=F(lm/A(ft)²
A=Area in square feet
D=Distance in feet
E=Illumination in footcandles
F=Luminous Flux in Lumens
I=Luminous
intensity (Candlepowe) in candles
Mired Shift Value = 1,000,000/d - 1,000,000/a
d=Desired
Color Temperature (no units)
a=Actual
Color Temperature(no units)
Fixture Lens Conversion Guide:
50° - 3.5Q5 / 360Q-4.5x6.5 (45°)
40° - 3.5Q6 / 360Q-6x9 (37°)
30° - 3.5Q8 / 360Q-6x12 (27°)
20° - 3.5Q10 / 360Q-6x16 (17°)
10° / 12° - 3.5Q12 / 360Q-6x22 (9.5°)
5° - None
8x8 (20°)
8x10 (16°)
8x16 (6°)
POWER CALCULATIONS
Power =
Voltage *
current (Watts = Volts * Amps)
P(w)=V(v)xI(a)
P=Electrical
Power (Wattage) in watts
V=
Voltage (
EMF), in volts
I=Electrical
Current(Amperage), in amps
Current =
Power /
Voltage (Amps = Watts / Volts)
RMS Volts = 0.707 * Peak Volts
RMS Volts = 1.11 * Average Volts
Ohm’s Law: V(v)=I(a)
V=
Voltage (
EMF), in volts
I=Electrical
Current (Amperage), in amps
R=Resistance, in ohms
Impedance: Z(Ω)=√[R²(Ω)²=X²(Ω²]
Z=
Impedance, in ohms
R=Resistance, in ohms
X=Reactance, in ohms
Power Factor: R(Ω)/Z(Ω)
pf=
Power Factor
R=Resistance, in ohms
Z=Reactance, in ohms
DC
VOLTAGE DROP OF
CONDUCTOR (cable) OF L LENGTH
V =
voltage drop, I =
current
R = resistance of
conductor per 1000 feet
L = length of
conductor in feet
R for 18awg = 6.51, 16awg = 4.09, 14awg = 2.58
12awg = 1.62, 10awg = 1.02, 8awg = 0.64
V = I * L * (R / 1000) * 1.004
Choosing the right
Stage Lighting Instruments: (Bulbtronics Which to Use? Pamphlet by Glen Cunningham for Bulbtronics 1998)
Beam Distribution Basic Terms: When you look at the total area of light, or “field,” projected by a
stage lighting
instrument you realize there are only a few basic variables: the magnitude of the center of the beam
intensity; the distribution of intensities throughout the entire field; the field’s focus; the character of shadows the field creates; the angle of spread; the shape of the field; the
color temperature; and the response to control.
The Magnitude of the Center Beam indicates how intense a field an
instrument projects. This, in turn, determines the brightness of an area on which it is projected of an area on which it is projected at any given
throw distance. For your design, you must match the
candlepower of the
instrument (measured in
candela) to the brightness you wish to have in the area it will light. The higher the
candlepower, the brighter the light. The brightness is determined by dividing the
candlepower by the square of the
throw distance.
The Distribution of Intensities refers to the
candlepower, or amount of light at every
point within the field. Mathematically speaking, it’s a distribution curve with the
candlepower as the Y factor of a
line graph and the degrees or distance away from the center beam as the X factor of the graph. Distribution curves very greatly, ranging from a very
flat filed with fairly equal intensities across the field, to a very highly-peaked field with a very intense center and a rapid drop-off away from center. Some popular field distributions resemble a classic bell-type curve with a bright center and a gradual decline in
intensity toward the outside.
No curve is better than another, since each
play a part in your design that another may not fill. “I remember using a 6"
fresnel with its
lens removed and its
reflector beaten up for one
effect on a show. By purist standards the field was horrendous - inefficient, uneven, and harsh, among other things - but it created the desired
effect better than any other
instrument.”
A
flat field is better for projecting silhouette patterns and slides, and when you use a single spot to light an area. Choose a highly-peaked field for lighting a relatively small, specific area (a “special.”) The bell-type curves are best for blending instruments to create a
wash some fields are
asymmetric, throwing more light away from a reference
line (normally a horizontal
line through the lamp, running parallel to the
stage floor) than near it. This is useful for creating even
cyclorama effects. You always can make compromises between distribution types, using for instance flatter bell-type curve for both projecting and blending a
wash, and a more peaked bell-type curve for both projecting and blending a
wash. There are no hard-and-fast rules, however. “I have used a very peaked field to great
effect for
gobo projection.
Field Focus is either hard or soft. A hard focus will produce a well-defined projected
image of anything at its
focal point and hard edges. A soft focus will project a poorly-defined
image and the field edges will have a soft, fading quality to them. You use a hard focus when you want to project the
image of either a silhouette
pattern (
gobo), including the round
gate of an
instrument for a hard spot, or when sharp, defined
shutter cuts are desired.
A Softer focus is better for lighting that is supposed to blend, and not supposed to indicate the direction of the source. It also can be used when projecting a
pattern to create texture with soft shadows. A soft-focus
instrument also will cast softer shadows on or behind objects it shines on - particularly useful when too many hard shadows make the scene too busy, change its character, or break its realism. “I often have used a break-up
pattern gobo with a soft focus to create the illusion of light shining through trees.”
The Angle of Spread defines how much of the
stage a single
instrument can
cover. All instruments have a
beam angle and a
field angle. The
beam angle is where you measure 50% of the center beam
candlepower (
cbcp). The
field angle is where you measure 10% of the
cbcp. A spot or special will want a smaller angle to help isolate it from other areas on
stage, a
wash will benefit from wider angle instruments, using fewer to
wash the entire
stage. The
beam angle often is used to determine on-center distances for blending a
wash.
Field Shapes vary greatly. Most are round, but some are square, oval, and rectangular.
Color Temperature is specific to the lamp used in an
instrument. The higher the
color temperature, measured in degrees Kelvin, the “whiter” the light is said to be. And the whiter the light is said to be. And the whiter the light the brighter it appears to be. So, using two instruments with color temperatures that differ greatly can create a bold contrast, or ruin an even
wash, depending on the circumstance. Higher
color temperature fields also project more vivid colors when gelled and so are good for bold colors washes and specials.
Response to Control refers to the rate at which the
instrument (and thus the field) changes when prompted. Some instruments, particularly those with large, heavy filaments,
lag a great deal from the time a
cue is executed to the time it actually finishes. This is a particular problem if the
lag is much slower than the
cue as you have designed it. A sharp
blackout is impossible if the
stage is washed with instruments whose fields are going to dim slowly down to black. In those cases, the best you may get is a fast
fade to black. The same problem occurs when you want to flash,
chase, or
strobe a bank of instruments. The slow burn-down can kill the
effect entirely.
Building your Lighting Sense: These field characteristics are the tone and timber of the light you will use to render your design. To those you add some of the instruments’ general mechanical abilities, such as
shutter cutting, barn-dooring, adjusting from a hard to soft focus, or narrow to wide spread. And, of course, each
instrument type provides you with its own unique capabilities. See table below for some of the field characteristics and mechanical abilities of the more common
instrument types. However, you will learn a great deal more about the character of the light projected by your instruments if you run some tests. Set up one of each of the
instrument types you have available, focusing them on an area representing a
stage with some furniture and people or objects. Be sure to choose instruments representative of those you will be using. If you don’t have access to the
stage itself, any area will do as long as you can get far enough away to look at the area being lit to see what the light actually does.
However, don’t just shine an
instrument onto a
flat wall and look at it. That’s not going to reproduce the conditions under which you will use it. You will be using equipment focused on varied surface textures and with many different objects on
stage. The
effect the light has on the atmosphere under those conditions is completely different than when you shoot it straight at a wall. And remember, creating with light is like painting with
broad strokes, not drawing with fine lines. Look at the overall field and the feel it offers.
When you have the instruments set up ( start off without any color,) carefully consider what you see the light doing. Look at the surfaces and objects that are being lit. Are there hard or soft shadows? Is a large or small area covered? Is there a hard or soft
edge to the beam? If the
instrument has some kind of shuttering or barn doors, are the cuts well defined or diffuse? Does the light punch through with an obvious indication of where
the light source is, or does it create a more general illumination, with less obvious directional quality to the field? What happens when the field is dimmed? Write down your observations - they’ll be useful as you
lay out a design.
If time and space allow, experiment by using pairs of instruments together - of the same type and different. See how their fields complement or contrast each other. How well do they blend or combine? This will be valuable time spent building an understanding of how to create the visions you wish to put on
stage. If you have never taken the opportunity to do this, regardless of how long you’ve used your equipment, try it. You may be surprised with some the characteristics you never noticed about the light that each
instrument type delivers.
Now look at each
wash, special, and
effect in your design, and write down any characteristics of light that would help them. Try to keep your descriptions brief, using single works like “hard,” sharp,” intense,” and “shuttered” when possible. When you’re finished, compare the list with the characteristics and capabilities of the instruments you have to work with. Look for the
instrument type that delivers the most characteristics for each
effect.
Sometimes you may find you don’t have enough instruments to fill every need, or even enough to go around. If you’ve gone through the process above, however, you can make intelligent compromises by deciding which characteristics are most important for each
effect and reserving the appropriate instruments for those effects, and getting the most out of the rest.
When you know what you want from an
instrument - and what you can expect from it - you can make more informed choices and compromises so your design works the best it possibly can using the tools available to you.
Ellipsoidal Reflector Spotlights: (Lekos) are usually specked out as 6x9, 6x16, 30 degree, mini-ellipse
etc, or brand name like 29°
Source Four or “Berkly” Also called
pattern unit, and spot light. Fixed focus and
zoom units are available.
units with an ellipsoid shaped
reflector, lenses in the front and framing shutters in between. The front lenses are mounted in a movable “
barrel” or
lens train. The
barrel allows the focus to change from sharp to moderately soft.
Zoom units have a variable size beam, which is adjusted by moving the lenses closer or further away from each other, as well as for fixed units by adjusting the focus some by moving the
lens train distance from the
reflector shorter or longer.
4.5x6 fixtures are 50° beam spread. 6x9 = 40°, 6x12 = 30°, 6x16 = 20° and 6x22 = 12° in general these
focal length and diameters are standard. All but the 6x16 is made up of two lenses, the 6x16 is made up of a single 6x22
lens. As the
focal length of the
instrument goes up, so does the distance the
lens must be from the
reflector, also the amount of magnification in the
lens goes down. with
focal length increases.
Fresnels are specked by
lens diameter, wattage, or model. Eg. as 6", 8",
inky, duce, 5K, tener. The
unit has a spheroid shaped
reflector and
fresnel lens in front. The
reflector and lamp move back and forward together inside the
unit to provide a variable size beam. The focus is always soft, and beam shape can be affected by barn doors and snoots (top Hats).
Scoops are specked by wattage and size. They are also called flood lights,
ellipsoidal reflector floods. the reflectors are large and elliptical sometimes used with a frosted lamp and no
lens. It is used for soft even lighting of a large area usually a
cyc or
backdrop.
Cyc Units are specked by wattage and number of cells also called a far
cyc or
Ianiro. These fixtures are open faced that use a linear
filament lamp and irregular
reflector to light a
cyc or
backdrop evenly from top to bottom. Usually wired for 3 or 4 color cells per
unit.
Strip Lights specked out by lamp type and wattage, length, and number of circuits or lamps. Used primarily for lighting drops or overall
stage toning, these units have a series of lamps wired to work in sets of 3 or 4 circuits. Lamps available include
MR16, Par38,
R40, Par56, Par64 & T-3 lamps from 50 to 1,000 watts.
Follow Spots: A high
intensity fixture that is generally used to highlight a single performer. and operator is required. Units range from small
incandescent units for small stages, to large HTI or Xenon (arc) lamps for arenas. Color changers are internal and can be customized. Most units have
iris and
zoom capabilities. Appropriate units are chosen by the
throw distance, and overall light levels on
stage. Designlab Chicago Rental Catalog 1.0 (1992) pp.6-10
Lenses - Focal Points: The relationship between the positions of
the light source or the object (slide,) and the
point where the transmitted rays from an
image is determined by the “
Lens Formula.” When P = the distance from the object to the principal plane of the
lens, Q = The distance from the principal plane to the
image, and F = The
focal length of the
lens; than 1/P+1/Q=1/F.
Focus of Focal Center: when the source (given the lamp is out of focus with its
reflector,) is moved forward from the principal focus, the reflected rays converge. When moved back from the principal focus, they diverge with a dark spot in the center of the beam. Also a bright half or partial moon like figure hanging around the center of the beam, denotes a lamp horizontally out of focus with the
reflector and its lenses in the opposite direction as is shown
Radius and
Focal Length: Lenses are about .52 times their
focal length by radius of curvature of the
lens. For
ellipsoidal lenses. ?
360Q Series
Safety Instructions and Operating Procedure, Alltman
Stage Lighting Co. Inc. 1996