Photopic Luminous Efficiency Function Research Articles

Measuring gloss using spectral reflectance

Abstract Gloss is historically measured at three angles of incidence, 20°, 60°, and 85°, using a light source filtered to replicate Illuminant C and a colored glass filter designed to reproduce the CIE 1931 photopic luminous efficiency function. Herein an alternate method that relies on the spectral reflectance of a gloss standard and the sample, both measured with a new reference gonio-spectrometer and in accordance with the geometries specified in internationally recognized standards, is presented. The spectral reflectance measured with the aid of a spectrometer is converted to luminous flux which is then used to calculate gloss. This alternate method eliminates the errors associated with the source actual spectral power distribution vs. that of Illuminant C, and the actual spectral transmittance of the colored glass filter used vs. the spectral distribution of the photopic luminous efficiency function. Gloss measurement results for a synthetic quartz sample, Suprasil 311, are presented. The measured values averaged over three reflectance measurements are 71.3 ± 1.2 (k = 2), 82.2 ± 0.9 (k = 2), and 98.1 ± 3.0 (k = 2), and these agree exceptionally well with the theoretical values of 71.3, 82.1, and 98.1 Gloss Units at 20°, 60°, and 85°, respectively. Components of uncertainty are discussed. In addition, a gloss scale is proposed. The components of the scale have been selected from readily available optical glass types for ease of fabrication and relatively low cost. They span a range from 4.4 to almost 170 Gloss Units for light at 20° angle of incidence.

Brightness perception under photopic conditions: experiments and modeling with contributions of S-cone and ipRGC

In 1924, the CIE published and standardized the photopic luminous efficiency function. Based on the standardized curve, luminous flux in lumens, luminance in cd/m^2, and illuminance in lux are determined by an integral of the curve and the incident light spectra in photometers and are considered physical brightness. However, human brightness perception is not only weighted by this simple determination, but is a more complicated combination of all L-cones, M-cones, S-cones, rods and later ipRGCs, which was partly described by the equivalent brightness of Fotios et al. with the correction factor (S/V)^{0.24}. Recently, new research has demonstrated the role of ipRGCs in human light perception. However, it is still unclear how these signal components of the human visual system are involved in the overall human brightness perception. In this work, human brightness perception under photopic conditions was investigated by visual experiments with 28 subjects under 25 different light spectra. In this way, the contributions of the signal components can be investigated. An optimization process was then performed on the resulting database. The results show that not only the L+M component, but also the S-cones and ipRGC play a role, although it is smaller. Thus, the visually scaled brightness model based on the database optimization was constructed using not only illuminance but also S-cones and ipRGC with R^2 of 0.9554 and RMSE of 4.7802. These results are much better than the brightness model after Fotios et al. using only S-cones (R^2 = 0.8161, RMSE = 9.7123) and the traditional model without S-cones and ipRGC (R^2 = 0.8121, RMSE = 9.8171).

Lighting simply made better: Providing a full range of benefits without much fuss

The effective application of lighting depends upon a definition of light that captures the full range of wavelengths to which the human retina is sensitive. The current definition of light, based upon the photopic luminous efficiency function, V(λ), does not. Rather, V(λ) is biased against short wavelengths that are important for some of the benefits that lighting can provide to people such as brightness perception and circadian regulation, thereby compromising the effective application of lighting. Neuroscience has revealed several visual and non-visual channels that emanate from the retina to different centers in the brain influencing our physiology and behavior. This research has also elucidated the spectral and the absolute sensitivities of these different neural channels. Since the definition of light and the many lighting standards do not reflect the neuroscience, they compromise the beneficial application of lighting. A new definition of light based upon the universal luminous efficiency function, U(λ), would be unbiased with respect to the full range of wavelengths to which the retina is sensitive. Coupled with scientific insight into the spectral and absolute sensitivities of the various neural channels, lighting can easily become more effective for delivering the benefits people expect.

A new rationale for setting light source luminous efficacy requirements

The photopic luminous efficiency function (V(λ)) is used internationally for the definition of light output from electric light sources (lumens) and thereby for regulating minimum luminous efficacy requirements (lumens per watt) for the manufacture and sale of light sources. V(λ) has, however, a long-wavelength spectral bias with respect to the overall spectral sensitivity of the human retina. When used in luminous efficacy regulations, the long-wavelength spectral bias of V(λ) effectively penalizes many of the benefits expected from lighting that can be provided by short-wavelength light (e.g. scene brightness, colour rendering, circadian regulation and off-axis detection). Regulators must use ad hoc reductions to luminous efficacy requirements for ‘cool’ light sources to ensure that lighting benefits can be provided to society. These reductions would be unnecessary if a luminous efficiency function representing the overall spectral sensitivity of the human retina were used instead of V(λ) in luminous efficacy regulations. The universal luminous efficiency function (U(λ)) is proposed as a replacement. Utilization of U(λ) would obviate ad hoc adjustments to regulations for ‘cool’ light sources, minimize wasted electric power imposed by regulations based upon V(λ), and perhaps most importantly, encourage manufacturers to produce light sources that efficiently provide multiple benefits to users.

Spectral considerations for outdoor lighting: Designing for perceived scene brightness

Photopic illuminance is the photometric metric used today for specifying parking lot lighting levels. The photopic luminous efficiency function does not represent the spectral sensitivity of the perceived scene brightness of parking lots. Sources with a greater proportion of short-wavelength radiation will be seen as brighter for the same photopic illuminance. Moreover, the psychological benefit of providing people with a sense of safety and security in a parking lot is better correlated with the perceived brightness of the parking lot than with its photopic illuminance. Because photopic illuminance is not predictive of the psychological benefit expected from the parking lot lighting system, electric energy will be unnecessarily wasted if specifications are based upon this metric. Specifying parking lot lighting with a benefit metric based upon perceived scene brightness could reduce electric power requirements as well as the amount of radiant energy reflecting from the pavement and escaping into the night sky. A method of equating brightness for different spectral power distributions is provided.

Toward a Definition of Circadian Light

Light is formally defined in terms of the photopic luminous efficiency function [V(λ)], but the spectral sensitivity of the human circadian system is poorly characterized by this spectral weighting function. A new definition of circadian light should be considered because of the impact that fabricated and natural light sources may have on human health and well-being. Establishment of a formal definition of circadian light could lay the foundation for a new generation of lighting professionals and better lighting standards.

Toward a model of outdoor lighting scene brightness

Light quantities based on the photopic luminous efficiency function do not predict brightness perceptions of lighted outdoor scenes such as streets, parking lots and plazas. This paper summarises a series of experiments conducted using scale-model outdoor scenes illuminated by different light sources to assess judgements of brightness. From the results and from previously published literature on the relative increase in short-wavelength spectral sensitivity for brightness, a tentative model for brightness perception of outdoor scenes is proposed. The model can serve as a starting point for efficiently testing future hypotheses regarding brightness perception in lighted outdoor scenes.

Spectral sensitivity for extrafoveal discomfort glare

Previously published evidence suggests that the discomfort glare response to bright lights has greater short-wavelength spectral sensitivity than implied by the photopic luminous efficiency function, V(λ). The present paper summarizes a series of experiments to characterize spectral sensitivity for discomfort glare from nearly monochromatic light sources presented in the near extrafovea (5° and 10° off-axis). The results are consistent with increased participation in the discomfort glare response from short-wavelength cones and greater short-wavelength sensitivity as eccentricity increases. From the results an empirical family of luminous efficiency functions, V DG(λ), for discomfort glare, is derived. Such data could have implications for specifications of roadway lighting, vehicle headlamps or other light sources that might contribute to discomfort glare.

３次元映像情報メディア技術 比視感度を利用したグレーティングイメージの高輝度化

３次元映像情報メディア技術 比視感度を利用したグレーティングイメージの高輝度化

生体リズムを考慮した光環境評価

Recent lines of research show that light is important not only to human vision but also to human circadian regulation. The photometric quantities based on the relative photopic luminous efficiency function are used to express lighting condition. However it has been shown that the spectra sensitivity curve for circadian regulation is different from the spectra sensitivity curve for the photopic visual system. In order to support lighting design considering circadian regulation, in this paper, a method to evaluate light based on melatonin suppression, one of circadian rhythms, was proposed. A formula, using spectrum distribution of radiant flux and action spectrum of melatonin suppression shown in a previous study, was developed to calculate the effect of light on human circadian regulation. Also a simplified formula was proposed in which illuminance and color temperature were used. The applicability of the simplified formula to actual spaces was tested by measuring light from lamps, the sun, and computer display and light in houses.

Does lighting need more photopic luminous efficiency functions?

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 VM(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 V10(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.

Autosomal Recessive Incomplete Achromatopsia with Deutan Luminosity

Four patients in three different families had a form of autosomal recessive incomplete achromatopsia not previously described. The visual acuity was 6/18 to 6/60 (20/60 to 20/200) with minimal ophthalmoscopic abnormality and normal fluorescein angiogram. The photopic electroretinographic responses were present in all four patients; the fusion rate of 60 Hz was only slightly subnormal. The high-intensity scotopic response was subnormal. The patients failed color screening plates and accumulated over 400 errors with scotopic axis on the Farnsworth-Munsell 100-hue test. The Rayleigh match was abnormal, displaced toward the red primary, but with normal luminance. The photopic luminous efficiency function was similar to that of the deuteranope. Color matching revealed a trichromatic form of color vision mediated by long wavelength and short wavelength cones, and a rhodopsin receptor.