Electrics

           

Lamps

 

 

 

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 U.S.) is about 120 V.

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.

Figure 9. Basic 2 pole synchronous machine

Figure 10. Flux voltage waveforms

A direct current is supplied to the rotor field winding through external slip rings. This d.c. field current, If , produces a magnetic field within the machine which has a N-S direction aligned with the axis of the field winding. The rotor poles are shaped such that the radial component of this field distribution varies sinusoidally around the inner stator surface. Thus, as the rotor is turned, the total magnetic field (referred to as flux linkage l ) linking a stator coil varies sinusoidally with time, at a frequency equal to the rotor speed, Figure 10a. Similarly, a sinusoidal voltage is induced in the coil proportional to the rate of change of flux linkage according to Faraday’s law. In a 2-pole machine one cycle of the induced voltage corresponds to one revolution of the rotor. However, because the individual phase coils are mechanically displaced by 120° , the peaks of the induced voltage of each phase are electrically separated by 120° , Figure 10b. Thus, a balanced 3-phase supply is created.

A practical phase winding, Figure 11, is made up of many stator coils, but the same basic principles apply. For example, the Mawdsley experimental machine has a total of 12 stator coils occupying 24 slots; each phase winding therefore consists of 4 coils connected in series.

 

Partially wound stator (Westinghouse Electric Corp.)

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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 United States. While these generally describe the utility supply, large industrial facilities may receive power at higher distribution voltage levels and derive the lower voltages internally. The voltages in the chart are the standard nominal supply values.

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

Nominal Voltages

Phase-Phase

Phase-Neutral

240

120

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.

TWO-WIRE

Nominal Voltages

Phase-Phase

Phase-Neutral

-

120

-

277

Used infrequently for residential service or industrial single-phase loads.

TWO-WIRE ISOLATED

Nominal Voltages

Phase-Phase

Phase-Neutral

120

-

240

-

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.

THREE-PHASE, THREE-WIRE

CORNER-GROUNDED DELTA

Nominal Voltages

Phase-Phase

Phase-Neutral

240

-

480

-

600

-

Used occasionally in industrial facilities with only three-phase loads. No neutral is available.

UNGROUNDED DELTA

Nominal Voltages

Phase-Phase

Phase-Neutral

240

-

480

-

600

-

Used occasionally in industrial facilities with only three-phase loads, or where isolation is required. No neutral is available.

OPEN DELTA

Nominal Voltages

Phase-Phase

Phase-Neutral

240

-

480

-

600

-

Similar to full delta, but used less frequently, for smaller three-phase loads.

UNGROUNDED WYE

Nominal Voltages

Phase-Phase

Phase-Neutral

480

-

600

-

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.

THREE-PHASE, FOUR-WIRE

GROUNDED WYE

Nominal Voltages

Phase-Phase

Phase-Neutral

208

120

480

277

600

347

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

Nominal Voltages

Phase-Phase

Phase-Neutral

240

120 (phases A & C)

 

208 (phase B)

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

Nominal Voltages

Phase-Phase

Phase-Neutral

240

120 (phases A & C)

 

208 (phase B)

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.
Filament: the substance, usually tungsten, which produces light when electricity is applied.
Base: the mechanical means of making a safe electrical connection.

The Bulb is given a name based on its shape.

”A” commonly found in your home.
”T” the tube shape is also very popular in fluorescent fixtures.
”G” the globe is often a decorative lamp used in make up mirrors.
”R” the reflector light has an inside coating that reflects light in one direction.
”P” the pear lamp has a distinctive shape with a reduced neck.
”ER” this lamp also has an inside reflective surface, shaped like an ellipse to focus light in a cone.
”PAR” the parabolic reflector in this sealed beam focuses light straight forward.


1/8ths of an Inch

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.

There are literally hundreds of bases, each one designed for its own type of fixture.

 

In the entertainment industry there are common types of bases.
They are….

 

Medium Screw Base

Mogul Screw Base

Medium Prefocus
Mogul Prefocus
Recessed Single Contact
Medium Two Pin

Mogul Two Pin

 

 

 

     

T20
Med Pf

T8 & T14
Med BiPost

T20
Mod Pf

T4
DC Bay

G6
2Pin Pf

T8
2Pin Pf

T3 & T5
RSC

T7 & T8
Med BiPost

PAR64
ExMogEndPr

PS52
Mog

T7, 8, 10,& 12
Mog Pf

T7 & T8
Med 2Pin

T12
Med Pf

T8
2Pin Pf

T6
Med 2 Pin

T5
2Pin Pf

T4
RSC

T4
RSC

PAR36
Ferrule

 

PAR36
Ferrule

 



T20
Mog BiPost

T24
Mog BiPost

 

T8
2Pin Pf

T4, T6, T7 & T8
Med Pf

T6
Med 2Pin

T7 & T8 Med BiPost

T3 & T5
RSC

 

 

 

PAR64
ExMogEndPr

T7, 8, 9, &10
Mog BiPost

T10
2Pin Pf

T7, 8, 9, 10,& 12
Mog Pf

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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 noon

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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