Lecture 8-Light And Colour

Question 1

What is colour temperature?

Answer 1

A measurement of colour from a light source, measured in K.

Question 2

What is white balance?

Answer 2

Refers to the colour temperature considered to represent white for the system. Cameras can either use presets or be calibrated to existing source, digital cinema cameras store white balance info in metadata.

Question 3

Colour temperature often doesn’t reflect the actual temperature of the light source:

Answer 3

Warm colour=low colour temperature

Cool colour=high colour temperature

Question 4

Define gels:

Answer 4

Heat resistant transparent polyester sheets in specific colours to accurately change source colour.
Gels do not add the colour we want, gels remove unwanted wavelength of light, a green gel filters out red and blue light.

Question 5

Define CTO:

Answer 5

Colour correction orange, makes daylight sources warmer (towards 3,200K and lower.)

Question 6

Define CTS:

Answer 6

Colour temperature straw, makes daylight sources warmer (towards 3,200K and lower but with less red than CTO.

Question 7

Define CTB:

Answer 7

Colour temperature blue, make tungsten sources cooler (toward 5,600K and higher).

Question 8

What strengths do CRO, CTS and CTB typically come in?

Answer 8

Full, 3/4, 1/2, 1/4, 1/8

Question 9

Define MIRED:

Answer 9

Micro reciprocal degrees- a measurement used to calculate shifts in colour temperature. MIRED=1,000,000/colour temperature. Colour correction gels have a MIRED shift rating, enables calculation of new colour temperature when gel is used.

Question 10

How do you calculate a MIRED shift?

Answer 10

1. Calculate the MIRED value for each target.
2. Subtract the current colour temperature value from the target colour temperature value.
3. Refer to a swatch book or gel guide to determine a suitable gel to use.
   MIRED SHIFT= (1,000,000/target temp)-(1,000,000/current temp).

Question 11

What gel should be used to convert light from a studio tungsten unit to standard daylight (5,600K)?

Answer 11

MIRED shift=1,000,000/target temp-1,000,000/current tempt
MIRED shift=10^6/5,600-10^6/3,200=-133
The gel that gives the closes shift is full CTB (-137).

Question 12

What else is a consideration when using gels?

Answer 12

Gels reduce the amount of light coming from the source.

Question 13

What are the transmission ratings from full CTB and 1/2 CTO?

Answer 13

Full CTO- 36% (about 1.5 stops less)
1/2 CTO- 73% (about 0.5 stops less)
How do you factor this is? Determine the required illuminance of the unit using the gel.

Question 14

How do you calculate the effect if a gel on illumination?

Answer 14

Required illumination=target illumination/gel transmission

Question 15

What does colour compensation (CC) refer to?

Answer 15

The amount of magenta (M) or green (G) needed to correct a source to a certain colour spectrum and colour temperature. You cannot directly calculate MIRED shift.

Question 16

What is a full plus green (30G)?

Answer 16

To convert daylight-balanced sources to cool white fluorescents, to convert tungsten sources to warm white fluorescents. Adds a green spike to mimic the spectrum of fluorescents.

Question 17

What is a full minus green (30M)?

Answer 17

to convert cool white fluorescents to daylight balance, removes the green spike to mimic the spectrum of daylight balanced lighting fixtures.

Question 18

What is a fluorofilter?

Answer 18

To convert cool white fluorescents to tungsten balance, removes the green spike to mimic the spectrum of tungsten lighting fixtures.

Question 19

What are diffusion gels used for?

Answer 19

To soften light, the stronger the diffusion the less distinct the shadows become, the stronger the diffusion the lower the transmission.