Evaluation of Light Measurement Instruments

Bruce Leigh Myers, Ph.D., Rochester Institute of Technology

Color critical applications require adherence to ISO 3664:2009 which outlines the minimum criteria to be met by color viewing systems. Among the criteria specified by ISO 3664:2009 are color temperature, chromaticity, spectral power distribution, and UV energy. Of these, color temperature is the most frequently discussed and monitored.

Many practitioners utilize different methods to ensure conformance to the ISO standard, including adherence to light booth manufacturer recommendations through standard operating procedures, test patches from, to assure simulation to D50 lighting, and third-party on-site services. Some color professionals have adopted spectroradiometers and other instruments to monitor color temperature: recently lower cost units have been marketed that have increased adoption among those who wish to more carefully monitor their standardized viewing.

The presently proposed study analyzes the agreement among instruments that measure color temperature, as well as benchmark the consistency of the measurement devices utilized.

The ITL 950 spectroradiometer from International Light Technologies, and instrument that is traceable to NIST will be used as a benchmark to test other instruments, including:

  1. ITL 950 spectroradiometer from International Light Technologies
  2. X-Rite i1 Pro 2
  3. Gossen Sixticolor Photographic color temperature meter
  4. Cine Meter II iPhone App ($24.99 from iTunes), requires Luxi Photosphere (22.45 from makers4good.com) Photographic color temperature meter.

The researcher proposes to visit a number of locations utilizing standardized viewing conditions in both RIT and at surrounding printers. Light booths from GTI, Just Normlicht, and X-Rite MacBeth will be analyzed.

In addition, a portable viewing booth from GTI (model: “Show Off”) will be used as a method of analyzing the consistency of the devices, and also as a means for evaluating the influence of ambient lighting on standardized viewing in the selected locations.

Research Questions:

  1. How much variance can be expected when reading color temperature using a ITL 950 Spectroradiometer?
  2. How much variance can be expected when reading color temperature with more readily available instruments (i1 Pro 2, Photographic light color meters).
  3. How close are the more readily available color measurement instruments to the Spectroradiometer?
  4. What is the influence in ambient light in normal working conditions to standardized viewing conditions in terms of color temperature?
  5. How much variation in color temperature is expected among viewing conditions selected?

Procedure:

A two Stage process is proposed.

Stage I:

In a dark room, the portable GTI unit will be set up so that it is the only source of illumination, and readings will be taken by each of the four light measurement instruments twice a day over a period of five consecutive days. In this manner, a benchmark of the consistency of the instruments and operation can be sought while controlling for the ambient light.

Stage II.a.:

Each of the four instruments will be used to read standardized viewing conditions at various locations throughout the RIT campus and nearby printing companies. The color temperature readings, which will include the influence of ambient light, will be recorded. This will represent the viewing as it is used in the field; data collected from this stage will be used to examine any variation in color temperature across multiple viewing conditions. In addition, if the consistency of each measurement instrument will be analyzed through each of the conditions, in this manner any condition that represents an outlier can be noted.

Stage II.b.

After the light with the ambient conditions is recorded at each respective location, the same portable light booth will be set up either in or adjacent to the existing light booth, and readings will be taken with the ITL950 Spectroradiometer. These readings can be compared to the readings from Stage I to ascertain any influence from ambient light in the normal working conditions.

Analysis Plan:

Research Question 1: How much variance can be expected when reading color temperature using a ITL 950 Spectroradiometer?

Analysis: Visually analyze date for normality and outliers using Q-Q test, paired t-test to examine if any differences are statistically significant.

Research Question 2: How much variance can be expected when reading color temperature with more readily available instruments (i1 Pro 2, Photographic light color meters).

Analysis: test-retest reliability assessed through a paired samples t test.

Research Question 3: How close are the more readily available color measurement instruments to the Spectroradiometer?

Systematic bias will be analyzed through an independent samples t-test, and proportional bias analyzed with an analysis of a Tukey Mean-Difference plot.

Research Question 4: What is the influence in ambient light in normal working conditions to standardized viewing conditions in terms of color temperature?

Analysis: Visually analyze date for normality and outliers using Q-Q test, paired t-test to examine if any differences are statistically significant.

Research Question 5: How much variation in color temperature is expected among viewing conditions selected?

Analysis: Range of color temperature readings graphically plotted and analyzed.