Lecture 7-Light, Lighting And Exposure Flashcards
Why do we use lighting fixtures?
To establish depth: for modelling,
To establish colour,
To direct the viewers attention,
To establish mood.
What is the illumination level measured in?
fc or lux
What are lighting fixtures source intensity ratings measured in?
Candelas (cd)
Lights are also rated by wattage (how much energy they use)
Source intensity is not always related to power: some lighting systems are more efficient than others.
What are the properties of tungsten units?
Lowel lights, red heads, blondes, babys, zip softs- robust, old technology but not very efficient. 3,200K colour temperature (tungsten balanced).
What are the properties if an HMI?
Hydragyrum medium-arc iodide
Arri HMIs
Discharge lighting units, reasonably energy efficient, 5,600K colour temperature (daylight balanced)
What are the properties of Kino Flos?
Fluorescent discharge technology, very energy efficient, low heat output, flexible colour temperature.
What are the properties of LED units?
Highest energy efficiency and very low heat output, flexible application, flexible colour temperature but limited spectrum.
Measuring intensity:
Illumination across the beam of light is not even, it is important to understand which part of the beam you are measuring.
Define hot spot:
The brightest area of the beam.
Define spread:
The main beam area that has a roughly even level of illumination.
Define Fall off:
The area between the edge of the spread and the edge of the beam.
How do you use the inverse square rule to measure intensity?
The level of incident illumination is inversely proportional to the square of the distance from the source. Illuminance=source intensity/distance ^2
fc=cd/ft^2
Lux=cd/m^2
You are shooting an interior scene in a store at night for a UK TV project but you want to simulate a sunny day. You are using an HPX171. The gaffer suggests using a 1.2K HMI fresnel shining through a window positioned about 7 feet away to stimulate sunlight. Is this a good choice?
Calculate the aperture required ogives the level of illumination in the store.
Luminance: 60,000cd/7^2=1,224fc
200fc is a typical illumination of a store
Yes the sunlight is within the latitude of the camera- 1124fc, 2.5 stops brighter than the store. The HMI is suitable because the illumination level can be adjusted easily.
200fc, exposure time for UK TV PAL is 25fps so exposure time is 1/50 sec, Exposure index of the HPX171 is ISO 500. f=(square root (fc x t x EI/ 25)) f=(square root (200 x 1/50 x 500/25)). Aperture needed is T 9
Possibly too much depth of field, use a ND filter 1/4ND reduces light by 2 stops, = T4.5
You are shooting a UK TV interview with a 35mm lens on a Sony F3 and you want your subject to have a medium depth of field in a close up. You want to use one 4-foot 4-bank Kino Flo as your key light. Can this work? If so, how far does it need to be from the subject (in meters)?
A close up with a 35mm on an F3 is about 1.5m from camera, using a depth of field chart, medium depth of field at 1.5m is T8, ISO 8 (EI). Lux=269xf^2/txEI
Illumination needed = (269 x 8^2) / (1/50 x 800) = 1,076 lux.
Candela rating for the kino flo is 5,000 cd: m=square root (cd/lux)
Distance=square root (5000/1076=2.16m
This can work because the init should be out of shot and is low heat.
Not a definitive distance only a guideline
What issues can effect lighting units intensity?
Age and condition of the bulb/lamp, atmospheric conditions, actual voltage of power source, line loss, condition of fixture lens and reflectors.
