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Spectrocal spectroradiometer

Manufactured by Cambridge Research Systems
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The SpectroCAL spectroradiometer is a versatile instrument designed for measuring the spectral power distribution of light sources. It is capable of accurately measuring the intensity and color characteristics of various types of illumination, including LED, fluorescent, and incandescent sources. The SpectroCAL provides precise data on the radiometric and colorimetric properties of the measured light, enabling users to analyze and characterize the light's performance.

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Lab products found in correlation

Matlab, by MathWorks (4 mentions) Bits visual stimulus generator, by Cambridge Research Systems (2 mentions) Display lcd monitor, by Cambridge Research Systems (1 mentions) Diamond pro 2070, by Mitsubishi (1 mentions) Matlab 7, by MathWorks (1 mentions)

7 protocols using spectrocal spectroradiometer

1

Spectroradiometric Calibration of Primary Displays

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All stimuli were generated using MATLAB version 9.2.0.556344 for Windows (The MathWorks, 2018). The output of each primary was measured independently in 8-bit colour range using a SpectroCAL spectroradiometer (Cambridge Research Systems) at regular intervals. Photon fluxes were calculated and linearly interpolated to obtain an input–output relationship for each channel. This was used to calculate the XYZ coordinates of each primary, which was then used to calculate intensities required to generate each coordinate. Successful calibration was confirmed by measuring output from projecting single colours from across the gamut (mean Euclidean difference in xy between target and presented colour coordinates = 0.0125 SD 0.004).
Gardasevic M., Lucas R.J, & Allen A.E. (2019). Appearance of Maxwell’s spot in images rendered using a cyan primary. Vision Research, 165, 72-79.
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2

Automated Visual Stimulus Generation

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Stimuli were generated in MATLAB (The MathWorks, Natick, MA, USA) using the Psychophysics Toolbox (Brainard, 1997 (link); Kleiner, Brainard, & Pelli, 2007 ; Pelli, 1997 (link)) and displayed using a Display++ LCD monitor (Cambridge Research Systems, Kent, UK) with a resolution of 1920 × 1080 pixels, a mean luminance of 59 cd/m2 and chromaticity x,y = {0.30, 0.33}. Observers viewed the screen from a distance of 1 m, at which it subtended 40 × 22 degrees of visual angle with a resolution of 48 pixels per degree. The display supports 10-bit color resolution, with 1024 intensity levels per color channel. Linearity of the output of each color channel was confirmed using a SpectroCAL spectroradiometer (Cambridge Research Systems). The measured emission spectra of the monitor primaries were integrated with psychophysically derived cone fundamentals (Smith & Pokorny, 1975 (link)) to create a linear transformation specifying the red, green, blue (RGB) values required to elicit any target triplet of cone excitation levels.
Jiang Z., Shooner C, & Mullen K.T. (2022). Achromatic and chromatic perceived contrast are reduced in the visual periphery. Journal of Vision, 22(12), 3.
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3

Conditioning Protocols with Gabor Stimuli

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High contrast sinusoidal grating stimuli (maximum Michelson contrast: 95 %), filtered with a Gaussian envelope (i.e. Gabor patches) and shown on a dark gray background, were the primary stimuli used in the current experiment. The luminance of the dark gray background alone was 1.4 cd/m2, and the ambient light level (defined here as the mean luminance of the wall facing the participant) was 0.4 cd/m2, as measured with a Gossen MavoSpot 2 luminance meter and cross-validated with a Cambridge Research Systems spectroCAL spectroradiometer. Viewed from a distance of 150 cm, all gratings spanned a visual angle of 5.7 degrees vertically and horizontally. Eight different Gabor orientations were created in Psychtoolbox 42 (link) running on MATLAB. A grating with 45° orientation (relative to a vertical 0° grating, see Figure 1, bottom) became the CS+ condition during the acquisition phase. Additional orientations of 15, 25, 35, 55, 65 and 75 degrees served as CS- conditions, and a −45° orientation as an additional control condition. To elicit ssVEPs, two phase-reversed versions of each Gabor patch were rapidly alternated during a given trial, at either 14 Hz (7 observers) or 15 Hz (8 observers). White noise, filtered between 1 and 3000 Hz, was used for both the startle probe (duration 50 ms) and the unconditioned stimulus (1000 ms), delivered over headphones at 98 dB SPL.
McTeague L.M., Gruss L.F, & Keil A. (2015). Aversive learning shapes neuronal orientation tuning in human visual cortex. Nature Communications, 6, 7823.
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4

Color Calibration and Stimulus Generation

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Stimuli were generated in MATLAB (The MathWorks, Natick, MA, USA) using the Psychophysics Toolbox (Brainard, 1997 (link); Kleiner, Brainard, & Pelli, 2007 ; Pelli, 1997 (link)) and displayed on a CRT monitor (Sony Triniton, Sony Electronics, New York, NY) with a mean luminance of 53 cd/m2 and chromaticity xy = [0.29, 0.30]. Observers viewed the screen from a distance of 80 cm, at which it subtended 22 × 27 degrees of visual angle. A Bits# visual stimulus generator (Cambridge Research Systems, Kent, UK) was used to control the amplitude of each color channel with 14-bit precision. Nonlinearity in the output of each color channel was characterized using a SpectroCAL spectroradiometer (Cambridge Research Systems) and corrected in software. The measured emission spectra of the monitor phosphors were integrated with psychophysically derived cone fundamentals (Smith & Pokorny, 1975 (link)) to create a linear transformation specifying the RGB values required to elicit any target triplet of cone excitation levels.
Shooner C, & Mullen K.T. (2020). Enhanced luminance sensitivity on color and luminance pedestals: Threshold measurements and a model of parvocellular luminance processing. Journal of Vision, 20(6), 12.
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5

Precise Calibration of Visual Stimuli

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Stimuli were generated in MATLAB (The MathWorks, Natick, MA, USA) using the Psychophysics Toolbox (Brainard, 1997 (link); Kleiner, Brainard, & Pelli, 2007 ; Pelli & Vision, 1997 (link)) and displayed on a CRT monitor (DiamondPro 2070; Mitsubishi Electric Corporation, Tokyo, Japan) with a mean luminance of 50 cd/m2 and chromaticity xy = {0.31, 0.33}. Observers viewed the screen from a distance of 80 cm, at which it subtended 22° × 27° of visual angle. A Bits# visual stimulus generator (Cambridge Research Systems, Kent, UK) was used to control the amplitude of each color channel with 14-bit precision. Nonlinearity in the output of each color channel was characterized using a SpectroCAL spectroradiometer (Cambridge Research Systems) and corrected in software. The measured emission spectra of the monitor phosphors were integrated with psychophysically derived cone fundamentals (Smith & Pokorny, 1975 (link)) to create a linear transformation specifying the RGB values required to elicit any target triplet of cone excitation levels.
Shooner C, & Mullen K.T. (2022). Linking perceived to physical contrast: Comparing results from discrimination and difference-scaling experiments. Journal of Vision, 22(1), 13.
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6

Automated Closed-Loop Color Calibration

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We used an automated closed-loop system to establish the proper RGB values for a given CIE coordinate’s chromaticity with our video stimulation system’s CRT. Each specified stimulation color from our set of 93 stimuli was assigned target coordinates for the calibration function xt yt Yt . We then presented a one-degree patch of the stimulus on the CRT with an initial arbitrary RGB test value and measured the video output with a SpectroCAL spectroradiometer (Cambridge Research Systems, UK). We corrected the error between the measured and desired CIExyY coordinates by adjusting the RGB values to reduce the error function (e), followed by a retest, using this formula:
e=xc−xtxt2+yc−ytyt2+Yc−YtYt2
Let xc, yc, and Yc be the measured CIExyY coordinates. This search algorithm repeated until the error was optimized to a level below 1% (e > 0.01), within the CRT’s RGB color space of R±1, G±1, B±1 . Once e ≤ 0.01 for each color and achromatic stimulus in our set, the RGB values were stored for use in our experiment.
Li M., Ju N., Jiang R., Liu F., Jiang H., Macknik S., Martinez-Conde S, & Tang S. (2022). Perceptual hue, lightness, and chroma are represented in a multidimensional functional anatomical map in macaque V1. Progress in neurobiology, 212, 102251.
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7

Visual Perception Experiment Setup

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The experiments were run in a dark room and were programmed using MATLAB 7.9 (MathWorks, http://mathworks.com) and the CRS Toolbox. The stimuli were presented on a NEC MultiSync FP2141sb color CRT monitor driven by a Cambridge Research ViSaGe graphic board with a color resolution of 14 bits per gun (Cambridge Research Systems, Rochester, United Kingdom). The monitor had a diagonal screen size of 22 inches, resolution of 1024 ´ 768 pixels, and a refresh rate of 120 Hz. The screen was calibrated using a SpectroCal spectroradiometer with the calibration routines of Cambridge Research Systems. A Cedrus RB540 response pad was used to collect observer responses (Cedrus Corporation; San Pedro, CA, USA). Observer position was stabilized by a chinrest so that the screen was viewed binocularly at a distance of 80 cm.
Devinck F, & Knoblauch K. (2023). Color appearance of spatial patterns compared by direct estimation and conjoint measurement. Journal of the Optical Society of America. A, Optics, image science, and vision, 40(3).
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