Due to the advantages of fast measurement speed, imaging luminance measurement devices (ILMDs) have become more and more popular in the recent years. However, even though an ILMD is corrected by flat field calibration, the measured results deviate from the real values when measuring curved surface sources. The deviation is larger in particular when the curvature of the source is smaller or when the source is unlike a Lambertian source. This paper shows how to obtain correction factors to increase the measurement accuracy of the ILMD when measuring different types of curved surface sources. The issue of how the measurement conditions affect the level of image blur is also discussed in this paper.

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The luminance and color of a traffic sign depend on the angle, illuminance, and spectrum of the illuminating sunlight. The general method for measuring the effects of sun on traffic signs is to use Xe source or Xe source with filters as a sun-simulator to simulate the CIE defined average sunlight spectrum, D65. The disadvantages of using the sun-simulator are the high cost and measurement error that arises from the difference between the spectrum of the sunlight and that of sun-simulator. Using Xe source as the sun-simulator may produce an error of around 3.5% due to the spectrum difference. To solve these problems, a measurement method has been applied to eliminate the need for sun-simulator in measuring the sun effect on traffic signs. Measuring the spectral reflectance of the target and calculating a luminance and illuminance translation factor allow us to calculate the luminance reflected from the target, regardless of the light source illuminating on it. For instance, the effects of other sunlight spectra, such as D55 or D75, on the targets can also be determined by this method without the use of any light source to simulate D55 or D75. The sunlight spectrum in the presented simulation equation is obtained directly from the CIE definition, eliminating the error associated with the difference between the sun simulator and sunlight spectra. The experimental results demonstrate that the calculated luminance is about 1% different from the measurement results. Low cost, good accuracy and high flexibility are the advantages of this method.

Ambient contrast ratio (ACR) is a useful parameter to evaluate the quality of displays when used under diffuse lighting conditions. The methodology recommended by most documentary standards calculates the ACR of the display from d:x reflectance. Reflectance measurement of flat surfaces typically employs an integrating sphere and a flat white reference plate. However, the shape difference between the flat white standard and test curved sample causes changes to the amount of light illuminating their surfaces and thus gives measurement errors. Especially for concave test surfaces, the error is significant when the sample has small radius of curvature. To increase the measurement accuracy, this paper derives the correction factor to compensate the effect caused by shape difference between the reference plate and test curved sample. The associated uncertainty analysis is also discussed in this paper.