Lecture 10 - Lighting Systems And Power Flashcards
What is the Gaffer, Best Boy, Electricians and grips roles on set?
Gaffer - ultimate person in charge of all lighting and electrical rigging- works closely with the key grip and DoP
Best boy - Electrician - is the gaffers assistant and typically handles logistical issues
Electricians - ‘sparks’ handle all wiring and lamp operation
Grips - handle all camera support and non-electrical rigging
What aspects need to be considered when evaluating a space for lighting?
Physical characteristics- dimensions, working space, building materials, dampness etc.
Existing lighting sources - windows, practical fixtures, skylights, adjacent light sources etc.
Attributes that could effect lighting - colour of paint on walls, reflectivity etc.
Existing power sources - capacity, integrity of systems/cables, locations of breakers etc.
Provision and location for cable runs - routing, length limits
Rigging positions - for lighting equipment, whether walls can be modified etc.
Location for staging areas - where equipment can be close to set but safely out of the way
What should lighting plans include?
A graphic representation of the set or location drawn to scale
Positioning of lighting fixtures and cable runs
Calculations for power requirements
Equipment lists for all required equipment
What is the gaffers primary concern?
Safety
Earthing cable runs - installed properly to accommodate ground or earth faults
Moisture - can dampness be controlled to ensure safe use of electricity
Load capacity - does the power supply being considered have adequate capacity
Cable capacity - can the cable accommodate the power needed
Heat - is there sufficient ventilation and cooling to accommodate all heat generated by lighting equipment
Fusing - is there sufficient protection within circuits on set or location to protect crew in case of faults
Trip hazards - can cables be ‘dressed’ and lighting units mounted in safe positions
All of this is in addition to the standard risk assessment.
What is electricity?
The flow of electrons through a conductor between positive and negative terminals
Direct current - flow is in one direction
Alternating current - flow constantly reverses, measured in cycles per second or Hz. U.K. AC is 50Hz, North America is 60Hz
What are the basic power units of measurement?
Amperage or current - (I) - the rate of flow of electrons, measured in amps (A)
Resistance (R) - the opposition to flow, measured in ohms Ω
Voltage (E) - the force that current flows through resistance, measured in volts (V)
Wattage or Power (P) - the total power being used, measured in watts (W)
What are the power equations?
P = I x E, power = amperage x voltage
Manipulate to solve for different units
I= P/E - for amperage
E= P/I
Power measurement is the same throughout the world but standards for power are different
U.K. and Europe - 230V, USA - 120V
Can we plug two 2K lights into a UK household socket?
Amps = watts/volts
2000/230V = 8.7A
8.7A x 2 = 17.4A
A standard uk household socket is rated at 13A, so no.
What is Ohms law?
The relationship between voltage, amperage and resistance.
I = E/R - amperage = voltage/resistance
Manipulate to solve for different units
E= I x R
R = E/I
Note: sometimes R is noted as K (kiloohms)
How do we know the resistance in our cables?
AWG - rating indicates cables current carrying capacity. The smaller the number the thicker the wire.
Resistance in cables is based on its thickness and the conductance of the metal used.
What is cmil and ampacity?
Cmil - measurement of the cross sectional area of the cable, measured in mils, 1mil = 1000th of an inch
The higher the number the greater the conductance and lower the line loss.
Ampacity is the maximum amount of current the cable can handle in amps. This varies based on distance. - if the amp rating is exceeded there is a risk of fire!
How does tripe conductor domestic cabling work?
Three wires - either a solid or twisted core, used for low to medium amperage fixtures, separate lines for ‘live’, ‘neutral’ and ‘earth’
In Europe: brown - live, blue - neutral, yellow and green - earth
In US - black - hot (live), white - neutral, green - earth
How does dual conductor domestic cabling work?
Two wires - either solid or twisted core, used for low amperage fixtures, ‘live’ and ‘neutral’ lines only, normally only used for DC fixtures.
The primary issue with this is there is no earth leg, so a short circuit will make the housing of the fixture ‘live’ thus dangerous.
What is line loss?
The drop in voltage in a cable due to resistance.
The longer the cable run, the greater the line loss
The larger the diameter cable, the greater the line loss
The larger the amperage, the greater the line loss
Too much line loss can alter colour temperature in tungsten fixtures and damage other electrical systems
Up to 5% voltage drop is acceptable
In Europe at 230V this equates to 11.5V
How do you calculate line loss?
Voltage drop = 2 x conductor resistance x amperage x length(ft)/cross section area of cable (cmil)
VD = 2 x R x I X L/Cmil
