One of the keys to understanding automated lighting, or any lighting, for that
matter, is to follow the flow of energy from the input to the output. A fundamental
law of nature is that energy can be neither created nor destroyed; it can only change
forms. Electricity is one form of energy, and the job of any lighting system is to take
electrical energy and efficiently convert it to light energy. In the real world, only a
fraction of the energy put into a lighting system comes out as visible light. Most is
lost to heat, some is lost to mechanical energy, and some is converted to invisible light
waves.
The process of converting electrical energy to light can be as simple as passing a
current through a filament to heat it up to the point where it gives off light, or it
can be a much more complicated process involving electronic switching power
supplies with voltage regulation, current regulation, and arc lamps. In automated
lighting, you will come across both of these scenarios, and it is imperative that you
understand them both. In each case, understanding begins with the concept of direct
current, or DC, electricity.
An electron is an electrostatically charged particle. Electricity is the flow of electrons.
When a voltage is applied to a conductor, the more loosely bound electrons in the
outermost orbit of the atom are pulled from their orbit and follow the path of least
resistance toward the higher voltage potential. When one electron is pulled away from
an atom, it leaves a “hole,” and that atom now carries a net positive charge in the
absence of the electron. The free electron will “drift” toward the higher potential,
colliding with atoms along the way. Each collision the electron encounters takes away
some of its kinetic energy and converts it to heat energy. As the kinetic energy of the
traveling electron is lost it slows down. The more it slows down, the more likely it is
to “fall” back into the orbit of another atom that has lost its outer electrons. This is
known as electron drift.
When a voltage is applied to a conductor, electrons are pulled from the outermost orbit
of the atoms. The free electrons move toward the higher potential, colliding with atoms
along the way. As the electrons collide, they lose energy and eventually “fall” back into
the orbit of an atom with a missing electron.
these interactions are going on at lightning speed, creating the massive flow of energy
due to the motion of the electrons. This is what we know as electricity. More
specifically, we refer to the flow of energy through the motion of the electrons as current.
In the process of the mass migration of electrons, the collisions between free electrons
and the larger molecules produce friction that heats up the conducting material. For a
given amount of current, the amount of friction produced is directly proportional to the
resistance of the conducting material.
In order for current to flow, there must be a conducting medium such as a wire or
cable. Some materials are better conductors than others because their molecules
contain atoms that more readily give up electrons. These materials are known as good
conductors, and they offer little resistance to the flow of electrons. Copper, gold,
silver, aluminum, and other metallic elements are good conductors and have a very
low resistance value (Table 4-1). Other materials such as carbon, wood, paper and
rubber are poor conductors of electricity. They are considered good insulators because
they inhibit the flow of electricity. Still others, such as germanium and silicon, will
conduct electricity under certain conditions and are known as semiconductors.
When we think of the direction of the flow of DC electricity, we tend to think in positive
terms. For example, if a current flows from left to right, then we tend to think of some
ethereal substance traveling from left to right. But electrons are negatively charged.
Therefore, when an electron travels from left to right, the standard convention is that the
current is flowing in the opposite direction (Figure 4-4). Only the U.S. Navy refers to
the direction of current flow as the same direction as the flow of electrons
Voltage, Current, and Resistance.
In the study of DC electricity, it is important to have a firm grasp of at least three basic
concepts: voltage, current, and resistance. Those three parameters are closely related in
an electric circuit. You already have a basic understanding of current, which is the flow
of electrons, and resistance, which is the resistance to the flow of electrons.
Voltage is sometimes referred to as potential because, like gravity, it has the potential
to cause something to happen. Gravity has a potential to make something fall, thereby
giving it kinetic energy; electricity has the potential to make electrons flow, thereby
producing electrical energy. In both cases, there is potential energy available.
A simple DC circuit is shown below. The battery provides the voltage that makes the
current flow when the circuit is completed. The wiring provides a path for the flow
of electricity, and it completes the circuit. The resistor prevents the current from
becoming too large and destroying the entire circuit. The load, in this case, is a light
bulb, but it might just as well be a motor, a fog machine, or anything that uses
electricity.
The water pressure from the reservoir forces water through the pipe, the flow restrictor
limits the amount of flow, and the flow valve turns the flow on and off. Bottom: The
voltage supplied by the battery drives current through the wires, the resistor limits the
flow of electricity, and the light bulb draws the current.
Series Resistance
When a series of resistors are connected in a circuit end to end, then the total value of
resistance is the sum of the individual resistors. They are said to be connected in series.
In the resistor network shown in Figure 4-8, the total resistance can be calculated by
adding the value of each resistor in series.
Rtotal
Rtotal
100 k
100,000
Rtotal
150 k
300 k
150,000
300,000
600,000 ohms
50 k
50,000
600 k ohms
Parallel Resistance
When two or more resistors are connected to common nodes, they are said to be
connected in parallel. To find the value of resistors in parallel, use the following
formula:
1
1
1
1
1
=+
+
+
…+
𝑅(𝑇)
𝑅1 𝑅2 𝑅3
𝑅𝑛
Ohm’s law is one of the most important fundamental relationships in elec- tronics. It
describes the mathematical relationship between the voltage, current, and resistance.
V (volts) = I (amps) □ R (ohms)
According to Ohm’s law, for a constant resistance, the current is directly proportional
to the voltage in a circuit; the higher the voltage, the higher the current. Alternatively,
for a constant voltage, the current is inversely proportional to the resistance; the higher
the resistance, the lower the current.
DC POWER
Ohm’s law is one of the most important fundamental relationships in elec- tronics. It
describes the mathematical relationship between the voltage, current, and resistance.
V (volts) = I (amps) □ R (ohms)
According to Ohm’s law, for a constant resistance, the current is directly proportional
to the voltage in a circuit; the higher the voltage, the higher the current. Alternatively,
for a constant voltage, the current is inversely proportional to the resistance; the higher
the resistance, the lower the current.
Alternating Current (AC)
The principle of induced current is the basis of AC generation. Once we have
established that we can induce a current by moving a conductor through the magnetic
lines of flux, building a generator is a simple matter of configuring a rotor with windings
that spin about an axis suspended in a magnetic field. As the rotor spins, the windings
rotate through the flux and generate a current.
If the phase angle between the voltage and current is zero, the power is simply the
product of the voltage and the current.
Transformer symbol showing the input voltage and the output
voltage.
Power (watts) = voltage (volts) □ current (amps)
POWER SUPLIES
THE DIODE
A diode, or rectifier, is a component that allows current to pass in one direction and not
the other. It acts as a sort of turnstile for electrons, letting them through as long as they are
traveling in the right direction.
Like most electronics components, a diode can be a discrete component or it can be
etched into an integrated circuit. Either way, it is made of a type. These materials are
made by “doping,” or adding impurities such as silicon, germanium, or selenium to a
semiconductor material. An N-type semiconductor has an excess of electrons, and a Ptype has a shortage of electrons or an excess of “holes.” When a junction is formed
between an N-type and a P-type material, it makes a diode. The lead connected to the Ntype side is called the cathode and the other lead is called the anode. When a positive
voltage is applied to the anode and a negative voltage is applied to the cathode, then the
diode is forward biased. The electrons in the N-type side are attracted to the positive
voltage on the opposite side of the junction, while the holes in the P-type are attracted to
the negative voltage on the opposite side of the junction. The electrons cross the junction
and fill the holes.
Alternatively, if the diode is reverse biased (positive voltage applied to the cathode and
negative voltage applied to the anode), then the electrons are pulled away from the
junction and no current flows.
In real life, there is a forward-biased threshold voltage below which no current will flow.
This is called the forward breakover voltage, which is
0.3 V for germanium diodes, 0.7 V for silicon diodes, and about 1 V for selenium diodes
the vast majority of discrete diodes in most electronics applications are silicon diodes.
Diodes are used for a variety of functions, one of which is voltage rectification in a power
supply. Voltage rectification is the conversion of AC to DC voltage or current.
In an AC circuit, a diode will conduct only during the positive half cycle of the waveform.
During the negative half of the cycle, the diode is reverse biased and does not conduct.
The result is a half-wave rectified waveform that is a type of pulsing DC.
Forward-biased diode showing electrons crossing the P-N junction and filling the holes
in the P-type semiconductor material. Bottom: Reversed- biased diode showing depletion
zone. No charges cross the P-N junction, and therefore no current flows. Full-wave
rectification converts the entire AC waveform to DC by reversing the direction of the
negative half of the sine wave. This is accomplished by using four diodes arranged in a
certain configuration called a full-wave bridge rectifier. The diodes in a full-wave bridge
rectifier conduct in alternating pairs depending on whether the AC voltage is in the
positive half cycle or the negative half cycle.
Voltage versus current in a diode. When the forward-biased voltage exceeds the turnon voltage, then current starts to flow. A reverse-biased diode will not conduct current
(except for the leakage current caused by the voltage drop across the junction) unless
the breakdown voltage is exceeded.
Symbol for a diode.
A single diode in series with an AC generator produces a half-wave rectified waveform.
When an AC input is fed to a full-wave bridge rectifier, one pair of diodes conducts during
the positive half cycle and the other pair conducts during the negative half cycle. The
result is a full-wave rectified DC waveform.
With an understanding of diodes and full-wave rectification, building a regulated DC
power supply is simply a matter of adding a few components. Figure 7-6 shows a schematic
diagram of the power supply for a Lightwave Research Track spot fixture.
The first step in the DC power supply is to convert the power from the line level voltage
to the maximum voltage required by the fixture. In this case both the fans and the motors
need 24 volts. A multi-tap transformer steps down the voltage from the line voltage to 24
VAC.
The next step is to rectify the AC voltage and convert it to a pulsing DC voltage. The
bridge rectifier is represented in the schematic in Figure 7-8 as a square block (Br1) with
four leads. The input is 24 VAC and the output is a fully rectified DC pulsing waveform.
After the bridge rectifier, the voltage is split into two separate rails: one for the motors and
one for the fan. The motor power supply rail is fused (F1) to protect it from current
overload. From there, a pair of 2200 microfarad smoothing capacitors (C41 and C42) filter
out the pulses in the waveform to convert it to a nonplusing steady DC waveform. The
capacitors filter out the ripples by holding a charge at the peak voltage. When the voltage
tries to drop below the peak, they provide the energy to keep the circuit at steady-state
DC voltage. When the voltage peaks, the capacitors recharge.
The Track spot power supply has a 5 VDC rail for the logic section, a 24 VDC rail for
motors, and another 24 VDC rail for the fan.
A multi-tap transformer accepts a line level voltage input and outputs 24 VAC,
Lighting design involves creating well-thought-out lighting solutions for various spaces,
considering both aesthetics and functionality. However, it is important to know the relationship
between lighting design and electricity production.
1.
Technical Understanding: Lighting designers need to master the technical aspects of
electricity, light sources, and vision. Understanding how different lighting equipment works and
how to create safe and effective designs.
2.
Energy Efficiency: Lighting design plays a crucial role in energy efficiency. By
maximizing daylight use and matching light quantity and quality to specific functions, designers
can reduce electricity consumption while maintaining visibility and comfort. Hence lighting design
combines science (electricity, optics) with artistic sensibilities to enhance architectural spaces and
meet human visual needs.
3.
Visual Impact and Aesthetics: Lighting design significantly influences the visual
experience of a space. It’s akin to architecture and interior design, emphasizing both form and
function. Different tasks require varying light levels. For instance, complex tasks demand higher
illumination, while non-critical areas can have lower levels. The Society of Light and Lighting
(SLL) provides valuable guidance on recommended lighting levels for diverse tasks and building
types Consider the interplay of direct and diffuse light: a balance between the two helps define
surface texture and facial features.
4.
Surroundings and Reflectance: The colors and reflectance of walls, ceilings, and furniture
impact lighting. Dark matte finishes absorb more light, potentially resulting in a gloomy space.
Opt for paler-colored surfaces to enhance light reflectance and maintain a pleasant ambiance.
5.
Energy Efficiency and Quality: Lighting design affects both energy consumption and
quality. LED lighting, recommended by energy consultants, offers a short payback period
(typically less than three years) and often comes with a five-year warranty