Electrics
Lamps
- Bulb Type
- Bases
- Color Temperature
- Visible Spectrum
- Red Shift
The Hydro Metaphor
Current
Current is the flow of electrons in an electric circuit. Flowing water is a good analogy of electricity. When water flows through a pipe, or down a stream, there is current.
Sometimes the current flows faster, and sometimes it flows slower. If we were to measure how fast the current was flowing in a pipe, we might say it was so many gallons per minute. When we measure how much current is flowing through a wire, it is based on the number of electrons flowing past that point in one second. There is a unit of measure called the Coulomb that enables us measure the amount of charge an object has (e.g. an electron). Since there are billions upon billions of electrons flowing through the wires, we instead measure the charge with the Coulomb, which is 6,240,000,000,000,000,000 (6.24 billion-billion) electrons.
When one Coulomb of electrons passes through a wire in one second that is one Ampere of current. Ampere is the basic unit of electric current. It is sometimes referred to as amps. When writing down a value of current, it is usually abbreviated with an "A" (e.g. 1 A = 1 Ampere).
Since we aren't able to "see" electrons or Coulombs of electrons, how do we tell how much current is flowing through a circuit? We use an ammeter to measure electric current.
Voltage
Water flows through a pipe because of water pressure. Water pressure forces the water to flow. Likewise, electromotive force (EMF) is the pressure that forces electrons to flow through a circuit. Electromotive force is also known as voltage. The basic unit of electromotive force is the Volt. 1 Volt could be abbreviated as 1 V.
If you wanted to measure how much voltage a circuit or battery had, you would use a voltmeter.
In your house, you have wires in the walls that carry electricity to lights
and plugs. The voltage in those circuits (if you live in the
Resistance
In the same fashion that only so much water can flow down or stream, or through a pipe, only so much current can flow in a circuit. Water is limited by the amount of friction it encounters as it flows. Electricity is limited by the amount of resistance it meets as it passes through a circuit. However, if we increased the water pressure in a pipe, more water would flow. If we turned up the voltage, then more current would also flow. Resistance limits the current that flows through a circuit for a particular applied voltage.
The basic unit of resistance is the Ohm. 1 Ohm could be written as 
(greek letter Omega).
In order to measure the amount of resistance in a circuit, you would use an ohmmeter.
Power
When
you combine current and voltage as factors, the result
is a measurement of power. In
electricity that power is called wattage.
Consequently the following formulas apply to our basic theatrical environment….
W=VA
A=W/V
V=W/A
Lamps
are commonly referred to by there wattage and type. Dimmers also have maximum power handling
capacities and are often stated in KW, 2.4 KW or 2400 watts.
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Wire Size
Just as a water pipe must be of a certain size and thickness to deliver the
desired water and pressure, so does electrical wire.
The general scale is inverted, so as wire size goes down the physical size goes
up. At 120v, our basic theatrical current,
consider the following chart.
|
AWG gauge |
Diameter Inches |
Ohms per 1000 ft |
Maximum amps at 120v |
|
OOOO |
0.46 |
0.049 |
400 |
|
OO |
0.3648 |
0.0779 |
200 |
|
0 |
0.3249 |
0.0983 |
175 |
|
1 |
0.2893 |
0.1239 |
150 |
|
2 |
0.2576 |
0.1563 |
125 |
|
4 |
0.2043 |
0.2485 |
100 |
|
6 |
0.162 |
0.3951 |
80 |
|
8 |
0.1285 |
0.6282 |
50 |
|
10 |
0.1019 |
0.9989 |
30 |
|
12 |
0.0808 |
1.588 |
20 |
|
14 |
0.0641 |
2.525 |
15 |
|
16 |
0.0508 |
4.016 |
10 |
Keep
in mind that wire size applies not only to the fixture being used but also to
the electrical cable that you may use to extend a circuit. Finally as cable length increases, voltage
goes down and equipment may fail to operate properly.
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Three Phase Synchronous Generator
Today, almost all electrical power is generated and transmitted as three phase a.c. The generator sets found in power stations consist of a prime mover, which may be a steam turbine, a gas turbine, or a diesel engine, and a 3-phase synchronous generator. Synchronous generators are the largest of all electrical machines with ratings of up to 1000 MW, and the development of several thousand MW sets is in progress. The principles of operation of a synchronous machine are independent of size, and practically all the important characteristics can be investigated on a small machine.
The basic construction of a 2-pole, 3-phase synchronous machine is shown in Figure 9. The rotor consists of two iron salient poles onto which are wound two concentric coils connected in series. The stator is a laminated iron cylinder, and is slotted to accommodate three sets of stator coils, displaced circumferentially at 120° intervals.
A direct current is supplied to the rotor field winding through
external slip rings. This
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ELECTRICAL SUPPLY CONFIGURATIONS
Following are the typical transformer configurations that
are used to supply 60 Hz power at 600 volts or less in the
Several of the systems are rarely used for new
installations, although they are still found in existing facilities. Other
arrangements exist that are used only occasionally or for special purposes, and
these have not been included at this time.
The colors green, green/yellow, white, natural gray, orange,
brown & yellow are reserved for specific conductors as defined by the NEC.
All other conductors may be any color except these. While the chart shows
typical color usage, some installations will differ.
SINGLE-PHASE
|
|||||||||||
|
|
THREE-WIRE
This is the most common supply
for residences and small commercial facilities. It is also used for the
offices in industrial facilities, where it may be derived from a higher
available voltage by means of a local transformer.
|
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|
|
TWO-WIRE
Used infrequently for
residential service or industrial single-phase loads.
|
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|
|
TWO-WIRE ISOLATED
Used to
prevent ground fault arcs in hazardous atmosphere areas in hospitals and
other similar applications. It may also be used as part of a power quality solution for
sensitive loads. Isolated sources are generally derived locally near the
point of use.
|
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THREE-PHASE, THREE-WIRE
|
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|
|
CORNER-GROUNDED DELTA
Used occasionally in industrial
facilities with only three-phase loads. No neutral is available.
|
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|
|
UNGROUNDED DELTA
Used occasionally in industrial
facilities with only three-phase loads, or where isolation is required. No
neutral is available.
|
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|
|
OPEN DELTA
Similar to
full delta, but used less frequently, for smaller three-phase loads.
|
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|
|
UNGROUNDED WYE
Used occasionally in industrial
facilities with only three-phase loads, or where isolation is required. The
center point may be grounded through a high
impedance, but no neutral is available.
|
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THREE-PHASE, FOUR-WIRE
|
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|
|
GROUNDED WYE
This is the most common system
for large commercial office buildings at 208 volts, or industrial facilities
at 480 volts with 277 volt lighting. All three phases can supply
phase-to-neutral loads.
|
||||||||||
|
|
CENTER-TAP GROUNDED DELTA
Used for commercial or
industrial facilities with primarily three-phase loads. The high leg (phase
B) must be identified, and is not usable for phase-to-neutral loads.
|
||||||||||
|
|
CENTER-TAP GROUNDED OPEN DELTA
Similar to
full delta, but used for smaller systems with minimal three-phase loads.
|
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Bulbs and Bases make a Lamp
|
|
It may sound elitist, but a light bulb is what you find in
your house. A lamp has components,
each with a specific function in mind.
A lamp has the following parts… Bulb: the glass envelope that surrounds the filament. |
|
|
There are two numbers used in describing a bulb. The first is for wattage or the power that the light will consume. The second modifies the general bulb shape by describing its diameter. Therefore a “100A17” describes a 100 watt household bulb, an “A” shape, that is 2 1/8th inches at its widest point. A “40T8” would describe a tube shaped lamp that is 1 inch in diameter and pulls 40 watts of electricity. It could be any length. A “Par 64” is a Par shaped lamp that is 8 inches across. Simple. |
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Lamp
Bases
|
|
Lamp bases safely connect the electrical wiring to the
filament and seal the filament in a vacuum. In the entertainment industry there are common types of
bases. Medium Screw Base Mogul Screw Base Medium Prefocus Mogul Two Pin |
|
T20 |
T8 & T14 |
T20 |
|
T4 |
G6 |
T8 |
T3 & T5 |
|
T7 & T8 |
PAR64 |
|
PS52 |
T7, 8, 10,& 12 |
T7 & T8 |
|
T12 |
T8 |
T6 |
T5 |
T4 |
|
T4 |
PAR36 |
|
|
PAR36 |
|
T20 |
T24 |
|
T8 |
T4, T6, T7 & T8 |
T6 |
T7 & T8 Med BiPost |
|
T3 & T5 |
|
|
|
|
PAR64 |
|
T7, 8, 9, &10 |
T10 |
T7, 8, 9, 10,& 12 |
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Color Temperature
Kelvin
Color temperature is a simplified way to specify the spectral distribution
curve of a light source. While in reality the color of light is determined by
its weight in each point of the spectral curve, the result can still be
summarized on a linear scale.
The resulting value is useful eg. for
determining the correct film in photography depending on the lighting situation
(resp. for determining the white balance in digital
photography), and for planning the right light source types in lighting design.
Note, however, that light sources of the same color
temperature can vary widely in the quality of light emitted. One may
have a continuous spectrum, while the other just emits light in a few narrow
bands of the spectrum.
Low color temperature implies warmer (more yellow/red) light while high color
temperature implies a colder (more blue) light. Daylight has a rather low color
temperature near dawn, and a higher one during the day. Therefore it can be
useful to install an electrical lighting system that can supply cooler light to
supplement daylight when needed, and fill in with warmer light at night. This
also correlates with human feelings towards the warm colors of light coming
from candles or an open fireplace at night.
Standard unit for color temperature is Kelvin (k).
(The kelvin unit is the basis of all temperature
measurement, starting with 0 k (= -273.16° C) at the absolute
zero temperature. The "size" of one kelvin
is the same as that of one degree Celsius, and is defined as the fraction
1/273.
Technically, color temperature refers to
the temperature to which one would have to heat a theoretical "black
body" source to produce light of the same visual color.
Some typical color temperatures are:
|
1500 k |
Candlelight |
|
2680 k |
40 W incandescent lamp |
|
3000 k |
200 W incandescent lamp |
|
3200 k |
Sunrise/sunset |
|
3400 k |
Tungsten lamp |
|
3400 k |
1 hour from dusk/dawn |
|
5000-4500 k |
Xenon lamp/light arc |
|
5500 k |
Sunny daylight around |
|
5500-5600 k |
Electronic photo flash |
|
6500-7500 k |
Overcast sky |
|
9000-12000 k |
Blue sky |
Visible Spectrum
Isaac Newton discovered in 1672 that light could be split into many colors by a
prism, and used this experimental concept to analyze light. The colors produced
by light passing through a prism are arranged in a precise array or spectrum
from red through orange, yellow, green, blue, indigo and into violet. The
students' memory trick is to recall the name "Roy G. Biv"
where each letter represents a color. The order of colors is constant, and each
color has a unique signature identifying its location in the spectrum. The
signature of color is the wavelength of light.
Fig. 1. The electromagnetic spectrum, which encompasses the visible region of light, extends from gamma rays with wave lengths of one hundredth of a nanometer to radio waves with wave lengths of one meter or greater.
. The visible light region occupies a very small portion of
the electromagnetic spectrum. The light emitted by the sun falls within the
visible region and extends beyond the red (into the infrared) and the ultraviolet (UV) with a maximum
intensity in the yellow.
When we consider light as an electromagnetic wave, a color's spectral signature
may be identified by noting its wavelength. We sense the waves as color, violet
being the shortest wavelength and red the longest. Visible light is the range
of wavelengths within the electromagnetic spectrum that the eye responds to.
Although radiation of longer or shorter wavelengths are
present, the human eye is not capable of responding to it.
Figure 2. A wave representation of three different light hues:
red, yellow-green and violet, each with a different wavelength
, which
represents the distance between wave crests.
As we move through the visible spectrum of violet, blue, green, yellow, orange
and red, the wavelengths become longer. The range of wavelengths (400 - 700 nm)
of visible light is centrally located in the electromagnetic spectrum (Fig. 1).
Infrared and radio waves
are at the long wavelength side while ultraviolet (UV), x-rays and gamma rays
lie at the short wavelength side of the electromagnetic spectrum. Radiation
with wavelengths shorter than 400 nm cannot be sensed by the eye. Light with
wavelength longer than 700 nanometers is also invisible.
We can describe light as electromagnetic waves with color identified by its
wavelength. We can also consider light as a stream of minute packets of energy-photons
- which create a pulsating electromagnetic disturbance. A single photon of one
color differs from a photon of another color only by its energy.
Figure 3. Diagram showing the visible region
of the electromagnetic spectrum in terms of wavelength and corresponding
energies. The visible region extends from 400 nm to 700 nm (wavelength)
with corresponding energies of 3.1 to 1.8 electron volts (eV).
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Dimming and Red Shift
Lamps are designed to emit a specific color temperature at
full voltage. Most
theatrical lamps burn at around 3200 K.
Other high pressure arc lamps burn brighter and hotter, at around 5600 K
As energy, or electricity is removed from a filament the color temperature
begins to drop. While this is happening
the nature of the wavelength is affected and it also begins to lengthen or
shift to the red end of the visible spectrum.
This is important because colored filters are often used. When the color temperature of a lamp begins
to shift to the red, so does the value of the pink light the fixtures was
producing. All of a sudden, a single
color gets a whole new range.
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