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PubMed1978

Colour discrimination in the frame of illuminating engineering. Effects of C and high-pressure Na sources at different illuminances.

Nowadays, people are encouraged to utilize colour information. In turn, the sources employed for both indoor and outdoor installations show a variegated gamut of spectral distributions. The colour rendering factor refers to the average observer, representative of the normal, young, adult, healthy population. In order to have an idea of the deviations from this ideal case, we have been undertaking a population study. The results up-to-date obtained by the use of the high pressure Na source are now briefly reported.

Adult↗
PubMed1997

An account of brightness in complex scenes based on inferred illumination.

Achromatic brightness matches between two small patches were measured in a display containing ten larger regions of different luminances. The spatial organization of the ten regions was varied while keeping constant the immediate surround (and thus local contrast) of each patch as well as the average luminance of the entire stimulus. Various spatial arrangements were designed to alter the illumination inferred by the observer without changing the ensemble of luminances actually in view. Some spatial arrangements of the ten regions were consistent with five (simulated) surfaces under two distinct levels of illumination, with one luminance edge within the display (an 'apparent illumination edge') dividing the stimuli into an area of lower illumination and an area of higher illumination. In other spatial arrangements the ten regions were configured so that no luminance edge in the display could be interpreted as an ecologically valid illumination edge that provides a parsimonious interpretation of the ten regions; these conditions were designed to induce observers to infer ten surfaces under a single illuminant. When the ten regions were arranged with an apparent illumination edge, the patch within the area of lower perceived illumination was perceived as dimmer than when the same patch and immediate surround were presented with no apparent illumination edge. The results are interpreted by positing that the apparent illumination edge causes an observer to group together regions under the same perceived illuminant, with a consequent effect on brightness: lowering or raising the level of a perceived illuminant causes a patch of fixed contrast to be perceived as less bright or more bright, respectively, just as occurs when lowering or raising the level of real illumination. It is suggested that changes in brightness in a complex scene that result from a change in real illumination may be caused by a difference in inferred illumination at the perceptual level, not by simply a change in the amount of light absorbed by photoreceptors.

Adult↗
PubMed2006

Material-illumination ambiguities and the perception of solid objects.

The appearance of objects depends on their material, shape, and on the illumination conditions. Conversely, object appearance provides us with cues about the illumination and the material. This so-called inverse problem is basically underdetermined and therefore we expect that material and illumination perception are confounded. To gain insight into the relevant mechanisms, we rendered a set of artificial spheres for vastly different canonical light fields and reflectance functions. We used four physics-based bidirectional reflectance distribution functions (BRDFs) representing glossy, pitted, velvety, and matte material. The six illumination conditions were collimated illumination from four directions, hemispherical diffuse illumination, and fully diffuse (Ganzfeld) illumination. In three sub-experiments we presented pairs of stimuli and asked human observers to judge whether the material was the same, whether the illumination was the same, and for a subset in which either the illumination or the material was the same to judge which of the two was constant. We found that observers made many errors in all sub-experiments. In experiment 2 the illumination direction was chosen at random. Using an interactive interface, we asked human observers to match the illumination direction of a sphere of one of the four materials with that of a Lambertian sphere. We found systematical material-dependent deviations from veridical performance. Theoretical analysis of the radiance patterns suggests that judgments were based mainly on the position of the shadow edge. In conclusion, we found no evidence for 'material constancy' for perception of smooth rendered spheres despite vast quantitative and qualitative differences in illumination and in BRDF between the stimuli. Although human observers demonstrated some 'illumination constancy', they made systematic errors depending on the material reflectance, suggesting that they used mainly the location of the shadow edge. Our results suggest that material perception and light-field perception are basically confounded.

Contrast Sensitivity↗
PubMed2000

Fractionated illumination in oesophageal ALA-PDT: effect on ferrochelatase activity.

BACKGROUND AND OBJECTIVE: Administration of 5-aminolevulinic acid (ALA) induces accumulation of the photosensitive compound protoporphyrin IX (PpIX) in certain tissues. PplX can be used as photosensitizer in photodynamic therapy (PDT). More selective or higher PpIX accumulation in the area to be treated could optimize the results of ALA-PDT. Porphobilinogen deaminase (PBGD) is rate-limiting in PpIX formation whereas ferrochelatase converts PpIX into haem by chelation of ferrous iron into PpIX. This results in a moment of close interaction (ferrochelatase binding to PpIX) during which ferrochelatase could selectively be destroyed resulting in an increased PpIX concentration. The aim of the present study was to investigate whether illumination before PDT can selectively destroy ferrochelatase. and whether this results in higher PpIX accumulation and thereby increases the PDT effect. Furthermore, the effect of a second ALA dose was tested. STUDY DESIGN/MATERIALS AND METHODS: Oesophageal tissue of 60 rats were allocated to 2 groups of 30 animals each. In one group, enzyme and PpIX measurements were performed after ALA administration (200 mg/kg orally, n=20), or a second dose of 200 mg/kg ALA at 4 h (n=10), half of each group with and without illumination at 1 h with 12.5 J/cm diffuser length. In the second group, PDT was performed. Ten animals were illuminated at 3 h after ALA administration with 20 (n=5) or 32.5 J/cm (n=5), 10 animals were illuminated at 1 h (12.5 J/cm) and received intra-oesophageal PDT treatment (20 J/cm) at 3 h (n=5) or 4 h (n=5) after ALA. Additionally, 10 animals received a second dose of 200 mg/kg ALA at 4 h and were illuminated (20 J/cm) at 7 h after the first dose of ALA with (n=5) or without (n=5) illumination at 4 h (12.5 J/cm). RESULTS: Illumination with 12.5 J/cm at 1 h after ALA administration caused inhibition of the activity of ferrochelatase at 3 and 4 h after ALA (P=0.02 and P<0.001, respectively), but not at 7 h (P=0.3). In animals sacrificed at 4 h the ratio PBGD:ferrochelatase was higher in animals illuminated at 1 h compared to non-illuminated animals (P<0.001). PpIX concentration was highest (42.7 +/- 3.2 pmol/mg protein) at 3 h after ALA administration and did not increase by illumination at 1 h. Administration of a second dose of ALA did not result in higher PpIX accumulation. After PDT, no difference in epithelial or muscular damage was found between the various groups. CONCLUSION: Illumination at 1 h after ALA administration can cause selective destruction of ferrochelatase, resulting in a higher ratio of PBGD:ferrochelatase. This does not result in accumulation of more porphyrins, even when a second dose of ALA is given. Therefore, under the conditions used in this study fractionated illumination does not enhance ALA-PDT-induced epithelial ablation of the rat oesophagus.

Aminolevulinic Acid↗
PubMed2003

Eradication of Propionibacterium acnes by its endogenic porphyrins after illumination with high intensity blue light.

Propionibacterium acnes is a Gram-positive, microaerophilic bacterium that causes skin wounds. It is known to naturally produce high amounts of intracellular porphyrins. The results of the present study confirm that the investigated strain of P. acnes is capable of producing endogenic porphyrins with no need for any trigger molecules. Extracts from growing cultures have demonstrated emission peaks around 612 nm when excited at 405 nm, which are characteristic for porphyrins. Endogenic porphyrins were determined and quantified after their extraction from the bacterial cells by fluorescence intensity and by elution retention time on high-performance liquid chromatography (HPLC). The porphyrins produced by P. acnes are mostly coproporphyrin, as shown by the HPLC elution patterns. Addition of delta-aminolevulinic acid (ALA) enhanced intracellular porphyrin synthesis and higher amounts of coproporphyrin have been found. Eradication of P. acnes by its endogenic porphyrins was examined after illumination with intense blue light at 407-420 nm. The viability of 24 h cultures grown anaerobically in liquid medium was reduced by less than two orders of magnitude when illuminated once with a light dose of 75 J cm(-2). Better photodynamic effects were obtained when cultures were illuminated twice or three times consecutively with a light dose of 75 J cm(-2) and an interval of 24 h between illuminations. The viability of the culture under these conditions decreased by four orders of magnitude after two illuminations and by five orders of magnitude after three illuminations. When ALA-triggered cultures were illuminated with intense blue light at a light dose of 75 J cm(-2) the viability of the treated cultures decreased by seven orders of magnitude. This decrease in viability can occur even after a single exposure of illumination for the indicated light intensity. X-ray microanalysis and transmission electron microscopy revealed structural damages to membranes in the illuminated P. acnes. Illumination of the endogenous coproporphyrin with blue light (407-420 nm) apparently plays a major role in P. acnes photoinactivation. A treatment protocol with a series of several illuminations or illumination after application of ALA may be suitable for curing acne. Treatment by both pathways may overcome the resistance of P. acnes to antibiotic treatment.

Acne Vulgaris↗
PubMed1996

Luminosity thresholds: effects of test chromaticity and ambient illumination.

Color constancy is often modeled on the assumption that color appearance in natural scenes is a function of the visual system's estimates of surface reflectance. Some stimuli, however, do not look like illuminated surfaces. Instead, they appear to be self-luminous. We hypothesized that the appearance of luminosity occurs when the visual system estimates a reflectance spectrum that is outside the gamut of physically realizable surfaces. To test this idea, we measured luminosity thresholds as a function of stimulus chromaticity and illuminant spectral power distribution. Observers adjusted the luminance of a test patch until it just appeared self-luminous. The test patch was spot illuminated by a computer-controlled projection colorimeter viewed in an experimental room lit diffusely by computer-controlled theater lamps. Luminosity thresholds were determined for a number of test patch chromaticities under five experimental illuminants. The luminosity thresholds define a surface in color space. The shape of this surface depends on the illuminant. We were able to describe much of the luminosity threshold variation with a simple model whose parameters define an equivalent illuminant. In the context of our model, the equivalent illuminant may be interpreted as the illuminant perceived by the observer. As part of our model calculations we generalized the classic notion of optimal stimuli by incorporating linear-model constraints. Given the equivalent illuminant, the model predicts that a patch will appear self-luminous when it is not consistent with any physically realizable surface seen under that illuminant. In addition, we show that much of the variation of the equivalent illuminant with the physical illuminant can be modeled with a simple linearity principle. The fact that our model provides a good account of our data extends the physics-based approach to judgements of self-luminosity. This in turn might be taken as support for the notion that the visual system has internalized the physics of reflectance.

Color↗
PubMed1987

Push-pull effect of surround illumination on excitatory and inhibitory inputs to mudpuppy retinal ganglion cells.

1. Changes in membrane potential and conductance were measured in on-centre and off-centre ganglion cells during the responses to illumination of different portions of the receptive field. 2. In on-centre ganglion cells the sustained depolarizing response to steady illumination of the receptive field centre was associated with a net increase in conductance. In the presence of centre illumination, stimulation of the surround with an annulus of light caused a hyperpolarization and a net decrease in conductance, and the reversal potential of the light-evoked response was shifted in a negative direction. In the absence of centre illumination the same annular stimulus caused a hyperpolarization and a net increase in conductance. 3. In off-centre ganglion cells the sustained hyperpolarizing response to centre illumination was associated with a net increase in conductance. In the presence of centre illumination, stimulation of the surround with an annulus caused a depolarization and a net decrease in conductance, and the reversal potential of the light-evoked response was shifted in a positive direction. In the absence of centre illumination the same annulus caused a depolarization and a net increase in conductance. 4. The results indicate that illumination of the receptive field surround can affect both the excitatory and inhibitory sustained inputs to a given ganglion cell in a 'push-pull' manner, by decreasing the synaptic input that was increased by centre illumination and increasing the synaptic input of opposite sign. The relative effect of a given surround illumination on these two inputs, and hence the sign and magnitude of the net conductance change, varied with the amount of centre illumination.

Action Potentials↗
PubMed1995

Suppression of flicker response with increasing test illuminance: roles of temporal waveform, modulation depth, and frequency.

This study examined the detectability of flicker for small foveal long-wavelength test stimuli centered within surrounding long-wavelength annular adaptation stimuli. Flicker threshold-versus-illuminance (tvi) curves were analyzed for four different test-stimulus waveforms--sine-wave, square-wave, and rapid-on sawtooth and rapid-off sawtooth flicker--at temporal frequencies ranging from 12 to 21 Hz and at temporal modulation depths ranging from approximately 50% to 100%. For all stimulus combinations that were examined involving temporal frequencies above 12 Hz, the resultant flicker tvi curves shared the following characteristic features: First, at operationally dim surround illuminances, there was always a single elevated threshold for detection of flicker. Second, some surround illuminance always could be found for which flicker threshold decreased abruptly, typically by approximately 1.5 log units within 0.1 log unit of surround illuminance increase. Third, when test illuminance was incremented above this lower flicker threshold, flicker always vanished; when test illuminance was incremented still further, flicker reappeared. Finally, at sufficiently bright surround illuminances flicker did not disappear with increasing test illuminance. Although these effects held for all waveforms, the abrupt decrease of flicker threshold occurred at brighter surround illuminances for sawtooth than for sine-wave flicker, and at brighter surround illuminances for sine-wave than for square-wave flicker, at least for fully modulated waveforms (of a given temporal frequency). Moreover, when modulation depth was adjusted so that any two different waveforms had the same first-harmonic contrast, the resultant flicker tvi curves became identical when plotted as first-harmonic amplitude versus surround illuminance. This identity held for any given temporal frequency, even though the flicker tvi curves for 12-Hz fully modulated sine-wave or square-wave flicker did not manifest flicker response suppression, whereas the flicker tvi curves for sawtooth flicker did. These and other results imply that the first-harmonic contrast of the test stimulus fully determines the shape of the entire flicker tvi curve and that the dc component of the test stimulus helps to cause flicker response suppression. The results also demonstrate that first-harmonic equivalence is only a necessary, not a sufficient, condition for linearity.

Female↗
PubMedDate not supplied

The importance of controlled illumination in color vision testing in a pediatric ophthalmology clinical practice.

The AO-HRR pseudoisochromatic plates are commonly used for color vision testing in pediatric ophthalmology; however, the recommended procedure for obtaining proper illumination (a completely darkened room and standard illuminant) is typically not followed. To evaluate the role of the illuminant in clinical testing with the AO-HRR, 132 children, ages 3 to 16 years, were tested with and without the recommended illuminant (MacBeth Easel Lamp) and with the self-illuminated APT-5 Color Vision Tester. Twenty-two failed the AO-HRR with the recommended illuminant; 28 failed the AO-HRR without the illuminant. Only 13 failed the APT-5. The Cochran Q test for three related samples showed that the differences among the three groups were significant (Q = 17.1, P < .001). Diagnostic evaluation following clinical screening indicated that the differences among the tests were primarily due to false alarms, which were greatest without the recommended illuminant and least with the APT-5. These results demonstrate the importance of controlled illumination in color vision testing, either by using the recommended illumination with the AO-HRR or a self-illuminated test such as the APT-5.

Adolescent↗
PubMed2006

Changes in the translucency of porcelain and repairing resin composite by the illumination.

OBJECTIVES: The objectives were to evaluate the difference in the translucency parameter (TP) by the illuminants, to determine the correlation between the contrast ratio (CR) and three TP values relative to the illuminants, and to measure the correlation between the differences in TP (DeltaTP) and color (DeltaE(ab)*) by the illuminants based on dental porcelain and porcelain repairing resin composites. METHODS: Color and spectral reflectance of three shades of one dental porcelain and three porcelain repairing resin composites were measured before and after thermocycling for 3000 cycles relative to the CIE standard illuminants D65, A and F2 over a white and a black backgrounds. Specimen was 1.8mm in thickness after polishing. CR was calculated, and the differences in TP and color caused by the change of illuminants were compared. Three-way analysis of variance by the material (porcelain or resin composite), shade and illuminant was used to compare differences (alpha=0.05). RESULTS: The TP value was influenced by the illuminant (p<0.05), and the TP values relative to the illuminants A and F2 were higher than those relative to D65. The correlation coefficients between the CR and three TP relative to the three illuminants were around -0.95. Color difference was positively correlated with the difference in translucency in resin composites (r=0.65 between A and D65 and 0.47 between F2 and D65), but was negatively correlated in porcelain (r=-0.37 between A and D65 and -0.69 between F2 and D65). SIGNIFICANCE: Difference in translucency by illumination should be considered when matching shade of porcelain and repairing resin composite.

Analysis of Variance↗
PubMed2006

Influence of illuminants on the color distribution of shade guides.

STATEMENT OF PROBLEM: Although a shade tab in a shade guide is matched to a natural tooth in the order of value, hue, and chroma, there are limited data on the color distribution of currently available shade guides sorted by these 3 parameters. Furthermore, spectrophotometric color measurements of shade tabs differ depending on the standard illuminant employed. PURPOSE: The purpose of this study was to determine the color distributions of 2 shade guides in value (CIE L( *)), chroma (C( *)(ab)) and hue angle (h(o)) scale relative to the standard illuminants D(65), A, and F2. MATERIAL AND METHODS: Color of shade tabs (n=36) from 2 shade guides (Vita Lumin and Chromascop) were measured, and the distributions for CIE L( *), C( *)(ab) and h(o) values were compared. Color differences of shade tabs depending on the illuminant were calculated. The distributions of the ratios of CIE L( *) and C( *)(ab) values of each shade tab compared with the lowest value tab or the lowest chroma tab were determined. The data for the value, chroma, and hue angle within each shade guide were analyzed with a 2-way ANOVA with the factors of shade designation and type of illuminant (alpha=.05). Color difference caused by change of illuminant was analyzed with a 2-way ANOVA with the factors of shade designation and pair of illuminants compared (alpha=.05). The Scheffe multiple comparison test was performed as a post hoc test. RESULTS: CIE L( *), C( *)(ab) and h(o) values were influenced by shade designation and type of illuminant in both shade guides. Color difference caused by change of the illuminant was influenced by the shade designation and pair of illuminants compared. The order of mean color differences of 16 Vita Lumin shade tabs by pairs of illuminants compared was as follows: DeltaE( *)(ab) (D(65)/F2) = 1.63 3.7). Color distribution of 2 shade guides by the value and chroma was not logical.

Analysis of Variance↗