The Influence of a Photometric Distance on Luminance Measurements
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Luminance measurements are the least frequent of all photometric measurements. This article characterizes and systematizes the various methods of luminance measurement. In particular, the method of direct luminance measurement using modern luminance meters (ILMD) is described in detail. This paper presents the results of the study on the influence of the measurement distance on the luminance measurement results. Two ILMD meters (laboratory and portable) and a luminance standard were used in this study. The conducted research showed that an incorrectly chosen measuring distance can lead to significant measurement errors of up to several tens of percent. In addition, the possible impact of incorrect measurements on the design of an interior lighting installation was presented. It was shown that the selected interior lighting installation can consume more than 40 percent more electricity compared to the installation based on the correct luminance measurements of the luminaires with diffuse shades. In the final stage of the study, the definition of the photometric test distance for luminance measurements using ILMD was proposed. The test results can be particularly useful for the luminance measurements of OLEDs or the luminaires with diffuse luminous character. However, these results can also be used for luminance measurements of other light sources and luminaires.Keywords:
Luminous efficacy
Luminous flux
In the luminance distribution of a lit sign, having no irregularities in brightness is desirable, that is, the uniformity ratio of the luminance should be good. The uniformity ratio is decided by various factors such as the number of lamps, the spacing of the lamps, the distance between the light source and the luminous surface, the inner surface reflectance, and the luminous surface reflectance. A simple prediction method to obtain the relationship between these factors and the uniformity ratio of the luminance was tested by using calculations on a two-dimensional surface. We found that the method was suitable, because the calculated and experimental results agreed with each other.
Luminous efficacy
Luminous intensity
Contrast ratio
Luminous flux
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Based on the experimental visual data obtained for self-luminous stimuli surrounded by a dark background, a new colour appearance model (CAM) for unrelated self-luminous stimuli, CAM15u, was previously developed. To extend the model to related self-luminous stimuli, the colour appearance of coloured self-luminous stimuli surrounded by a luminous background was evaluated using the magnitude estimation method. Experiments have been performed in Belgium and in Argentina using two different experimental setups. With a LED setup in the Belgian laboratory, visual data on the perception of brightness, hue and amount of white of 30 coloured self-luminous stimuli surrounded by a luminous background were collected. Luminance levels of the stimuli and the background were respectively 50 cd/m2 and 28 cd/m2 (positive contrast condition). With a projector setup in the Argentinian laboratory, visual data on the perception of brightness and amount of white of 32 coloured self-luminous stimuli surrounded by a luminous background were collected. Luminance levels of the stimuli and the background were respectively 10 cd/m2 and 5.6 cd/m2 (positive contrast condition). For both experiments; the brightness scaling shows a clear and prominent Helmholtz–Kohlrausch effect. This effect describes the impact of the saturation of a stimulus on the perceived brightness and has been seriously underestimated in earlier CAMs. Both brightness, hue and amount of white are found to be well predicted by CAM15u, for this positive contrast condition.
Hue
Luminous flux
Luminous efficacy
Sensory threshold
Stimulus (psychology)
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In 1924 the Commission Internationale de l’É clairage (CIE) established the photopic luminous efficiency function, V(γ), that subsequently has been used to measure luminance. Some have assumed luminance to be synonymous with brightness. Luminance is based mainly upon flicker photometry, and this methodology does not provide data predictive of the apparent brightness of steadily viewed lights. This paper discusses alternative photopic luminous efficiency functions that could be used for measuring luminance. A proper treatment of brightness is outside the scope of the present paper, although the CIE is actively studying this topic. Moreover, this paper does not discuss the scotopic luminous efficiency function established by the CIE in 1951. Vision research conducted since 1924 using methodologies other than flicker photometry has shown that the V(λ) function slightly underestimates human foveal spectral sensitivity at short wavelengths in the visible spectrum. This has been partly corrected by recommending the V M (λ) luminous efficiency function, but it has been used only by the research community. Further research using both physiological and psychophysical techniques have shown that there are several visual pathways between the eye and the cortex that mediate visual information. For example, the CIE is investigating the adoption of a provisional V 10 (λ) luminous efficiency function to characterize luminance for off-axis stimuli. Lamp manufacturers and illuminating engineers should be clear that the classical V(λ) function does not predict luminance under all conditions, although it remains a useful measure of the luminance of foveal visual tasks and for describing acuity and reaction time.
Scotopic vision
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Mesopic vision
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Luminous flux
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The usual engineering interpretation of luminance (photometric brightness), luminous intensity per unit projected area, is adequate for many applications. However, the basic definition involves a limit of two independent variables, area and solid angle. Luminance is luminous flux per unit projected area per unit solid angle. Using this definition it is possible to explain why meters never exactly measure luminance and to determine what functions of luminance produce the responses of luminance meters. — All meter measurements and practical applications of luminance involve some type of averaging process. Generally, this presents no problem. There are many cases, however, in which a precise definition of the average must be based on the application since two independent variables are involved. It is important to recognize when this is required. This is especially true in scientific applications and in the design and analysis of luminaires, light sources, projection systems, and other optical systems. Many different values of luminance can be used to describe a light source, and it is important to choose the appropriate definition for each use.
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Summary form only given, as follows. AC-plasma display panel (AC-PDP) is using gas discharge display device which has great potential as a flat display with large display area and high brightness. Because of their high picture quality, light weight, and large screen size, these are now attracting considerable attention in digital broadcasting for use in suitable TV monitors. However, the present-day PDP with a luminous efficiency of typically about 1.0 lm/w is low in comparison with a CRT (5 lm/w) and limits the brightness. Improvement of the luminous efficiency is, therefore, a key factor to obtain a better panel performance. In this research, in order to increase the luminous efficiency of PDP, three new types of AC-PDP cells have been proposed and investigated. New-shaped types of electrodes were developed for high luminance coplanar type AC-PDP. The new-shaped type electrodes had been 3 types in one cell, A, B, and conventional type, respectively. The new-shaped type electrodes that have been developed have a lower breakdown voltage than the conventional type electrode at normal pressure. Also, the luminance efficiency is improved by about 20% at the same firing voltage. This result means that the currents are limited by characteristics of the new-type electrode.
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Flat light guides are modern solution enabling production of luminaries characterised by large area and low height. The amount of the luminous flux, which might penetrate the side-lit flat light waveguide with a predefined thickness depends on the light source's luminance. Special fluorescent lamps equipped with an internal reflector layer were designed for this kind of illumination systems. Such lamps are typically characterised by small aperture along the spine of the lamp. The aperture technology boosts the luminance value within the lamp's aperture to levels even 4 to 5 times higher than the average luminance of a standard fluorescent lamp. The presented article contains a detailed analysis of the impact of the aperture angle size on the coupling efficiency. It was also shown that application of a mini aperture fluorescent lamp influences changes in the luminous intensity curves of prismatic elements, which are most commonly used to direct the luminous flux.
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Fluorescent lamp
Aperture (computer memory)
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Luminous intensity
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Fluorescent light
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Sufficient illumination enables the observer to identify the true colors of an object captured by an imaging sensor, whereas dim illumination restricts proper observation. This paper proposes a single image enhancement algorithm based on human visual system. First, the image is transformed by the proposed Luminance Perception procedure from the spatial domain into the proposed Brightness Domain, where the image can be assessed as to whether or not it has sufficient illumination. Further, if the image is determined to have insufficient illumination, the assessed range of insufficient illumination and sharpness is used to restore the image's true illumination and textures to best fulfill the requirements for human visual perception. Our experiments show that the enhanced images generated by the proposed algorithm exhibit more brightness and appreciably better contrast than those generated by other state-of-the-art image enhancement algorithms that use images captured under various illuminant levels in various kinds of natural scenes.
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Human eye
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The concept of a high-luminance light source based on luminescent conversion of LED light and optical concentration in a transparent phosphor is explained. Experiments on a realized light source show that a luminous flux of 8500 lm and a luminance of 500 cd/mm2 can be attained using 56 pump LEDs at 330 W electrical input power. The measurement results are compared to optical simulations, showing that the experimental optical efficiency is slightly lower than expected. The present status enables applications like mid-segment digital projection using LED technology, whereas the concept is scalable to higher fluxes.
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Luminous efficacy
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Four kinds of traffic lighting sources HPS, MH, LED and EDL are widely used in roads and tunnels, the luminance at this place almost in the range of 1-10 cd/m 2 , which is the mesoptic vision. The mesoptic luminous efficiency can be calculated from photopic vision spectral luminous efficiency function. The results indicate that HPS’s luminous efficiency increased with improve of adaptation brightness, while the rest three kinds of light sources’ luminous efficiency reduced. At the same luminance level, HPS, MH, LED and EDL’s mesoptic luminous efficiency reduced in turn.
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The fundamental goal of color appearance research is to establish a correlation between the optical properties of stimuli and their corresponding perceptual attributes. Stimuli seen on a self-luminous background occur frequently in everyday situations when viewing lamps and luminaires, luminous panels with light emitting diodes (LEDs) and organic light emitting diodes (OLEDs), traffic signals, and advertisements. In this article, the impact of the luminance of a neutral self-luminous background on the brightness perception of neutral self-luminous stimuli was investigated in a series of magnitude estimation experiments. A brightness model has been developed with the spectral radiance from stimulus and background as input. The cone excitations are calculated using the CIE 2006 10° cone fundamentals. Luminance adaptation to the background is included by adopting a background-dependent semisaturation constant in the Michaelis-Menten function modeling cone response compression. The performance of the model is very good if negative and positive contrast scenes are modeled independently.
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Stimulus (psychology)
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