Lesson 10

The Reading Module

Read the text: Correlated color temperature

CIE (1931) xy chromaticity diagram including the Planckian locus, with temperatures indicated. Wavelengths of monochromatic light are shown in blue. The lines crossing the Planckian locus are lines of constant correlated color temperature.

The Kelvin system for lamp description works well for an incandescent lamp. Since there are very nearly black body radiators, their chromaticity coordinates land directly on the Plnckian locus in the CIExy color space. Fluorescent lighting is not incandescent and presents a new challenge. Fluorescent lamps are made using myriad combinations of phosphors and gases. The illumination that they produce is almost never described by a point in color space that lies on the Planckian locus.

The question then becomes how to describe the quality of light from a fluorescent lamp. The method used is called the “non-elated color temperature”, which is a method for assigning a color temperature to a color near, but not on, the Planckian locus. The above plot shows lines crossing the Planckian locus for which the correlated color temperature is the same. Nevertheless, the colors are not the same, and the method gives only an approximate specification of a particular color. Due to this shortcoming, the rated CCT of any fluorescent tube does not completely specify its color.

To be more precise: a number of color spaces have been developed in which the distance between them on a chromaticity diagram may estimate the difference between two colors. There include the 1960 CIELuv (which is now outdated) and the 1976 CIELuv’v’ and CIELab spaces. On a chromaticity diagram for which distances specify color distances, the best estimate of the color temperature of any point will be the color temperature of the point on the Planckian locus closest to that point. Although it is outdated, the CIE specifies distances in the 1960 CIELuv chromaticity space to define correlated color temperature.

Photographers often use color temperature meters. Color temperature meters are designed to read only two regions along the visible spectrum (red & blue), more expensive ones read three regions (red, green & blue). They are almost useless under fluorescent light. There are general guidelines and some specific filters recommended to obtain optimum quality under such frustrating circumstances.

I. Reading exercises:

Exercise1. Read and memorize using the dictionary:

chromaticity diagram, locus, constant correlated color temperature, incandescent lamp, fluorescent lighting, myriad combinations, non-elated color temperature method, visible spectrum

Exercise 2. Answer the questions:

1. What is chromaticity diagram?

2. What are fluorescent lamps?

3. What is “non-elated color temperature” method?

4. What are color temperature meters designed for?

Exercise 3. Match the left part with the right:

1. The method used is called the “non-elated color temperature”	1. in which the distance between them on a chromaticity diagram may estimate the difference between two colors.
2. A number of color spaces have been developed	2. color temperature meters.
3. Photographers often use	3. which is a method for assigning a color temperature to a color near Planckian locus.
4. Fluorescent lamps are made	4. using myriad combinations of phosphors and gases.

Exercise 4. Open brackets using the right words:

Color temperature meters are almost (useless/useful) under fluorescent lamps.

The Speaking Module

II. Speaking exercises:

Exercise 1. Describe chromaticity diagram; fluorescent lighting; myriad combinations; non-elated color temperature method; visible spectrum using the suggested words and expressions:

chromaticity diagram include; locus; temperature; indicate

fluorescent lighting incandescent, fluorescent lamp; myriad combinations; phosphors; gases

myriad combinations fluorescent lamp; make; use; phosphors; gases; illumination; describe; point; color space

non-elated color temperature method assign; color temperature; near; locus

visible spectrum color temperature meters; design; read; region; expensive

Exercise 2. Ask questions to the given answers:

1. Question: ____________________________________ ?

Answer: Fluorescent lamps are made using myriad combinations of phosphors and gases.

2. Question: ____________________________________ ?

Answer: The Kelvin system for lamp description works well for an incandescent lamp.

3. Question: ____________________________________ ?

Answer: The non-elated temperature method gives only an approximate specification of a particular color.

4. Question: ____________________________________ ?

Answer: Photographers often use color temperature meters.

The Writing Module

III. Writing exercises:

Exercise 1. Complete the sentences with the suggested words: on; of; closest; on; are made; best; may; using

Fluorescent lamps _____ _____ myriad combinations _____ phosphors and gases. _____ a chromaticity diagram the _____ estimate of the color temperature _____ any point will be the color temperature of the point _____ the Planckian locus _____ to that point.

Exercise 2. Fill in the table with words and expressions from the text:

Color temperature meters are designed
Color temperature meters are almost useless
The lines crossing the Planckian locus are lines

Exercise 3. Compose a story on one of the topics (up to 100 words):

“Chromaticity diagram”

“What is ‘non-elated color temperature’ method?”

“Color temperature meters”