Work environment. Retina anatomy. A human eyeball is like a simple camera! The way of vision signal. Directional sensitivity. Lighting.

Transcription

1 Eye anatomy Work environment Lighting 1 2 A human eyeball is like a simple camera! Sclera: outer walls, hard like a light-tight box. Cornea and crystalline lens (eyelens): the two lens system. Retina: at the back of eyeball, like a film. Iris: like diaphragms or a stop button in a camera Pupil: camera aperture Eyelid: lens cover. Retina anatomy Rods contours and motions Low resolution ~7 mln Cones colours High resolution ~120 mln 4 The way of vision signal Directional sensitivity 1. Retina 2. Optic nerve 3. Optic chiasm 5 1

2 Vision variations Photopic (daily) vision cones and rodes vision; color vision under normal lighting conditions during the day; sharp image on fovea, general perception on peripheral area Scotopic (night) vision - primarily rod vision under low lighting conditions; image with low resolution, motions easy to notice Mesopic vision - combination of photopic vision and scotopic vision in low but not quite dark lighting situations; cones work partially 7 8 Rodes and cones sensitivity Main vision mechanisms "red" cones (64%)) "green" cones (32%) "blue" cones (2%) Adaptation Accommodation Convergention 9 10 Adaptation good vision at changing lighting levels Alternations of an iris diameter 2-8 mm Light intensity alternations 1:20 Photochemical adaptation of cones and rods A. Cones B. Rods Accommodation good vision at changing distances Muscles relax, long focal length Muscles tense, short focal length

3 Convergention 3D vision A single target observed by two eyes Very fast mechanism (<~0.5s) Better in good lighting conditions Vision diagnostics Snellen charts Standard eye Nearsightedness (myopia) Farsightedness (hyperopia)

4 Astigmatism Gestalt rules perception of figures and background a) environment b) symmetry c) convexity d) orientation e) Light and contrast f) area Gestalt laws of perceptual grouping Gestalt laws of perceptual grouping Proximity Proximity Similarity Similarity Continuation Continuation Closure Light Lighting energy radiated over wavelengths sensitive to the human eye, from about 330 nm to 780 nm

5 Basic measures Φ - Luminous Flux [lm] Luminous flux Φ [lm], Intensity I [cd], Illuminance E [lx], Luminance L [cd/m2]. 25 a very basic unit of measurement for light; photometrically weighted radiant flux (power) factored by the sensitivity of the human eye energy per unit time (dq/dt) that is radiated from a source over visible wavelengths If a uniform point light source of 1 cd luminous intensity is positioned at the center of a sphere of 1 m radius, then every area of 1 m 2 on the inside of that sphere will receive a luminous 26 flux of 1 lm I - Luminous Intensity [cd] E - Illuminance [lx] the luminous flux emitted from a point per unit solid angle into a particular direction 1 candela about the intensity of a normal wax candle! luminous flux density the quantity of practical importance in judging whether an area is lighted well enough for visual tasks 1 lux is defined as a lumen per square meter Basic photometric measures L - Luminance [nit = cd/m2] used to characterize the "brightness" of flat emitting or reflecting surfaces a measure of how much the eye is stimulated and therefore of how great an impression of brightness is created in the brain the nit is the unit of luminance and is defined as a candela per square meter

6 Lighting comfort EN Standard The Lighting of Workplaces (Polish Standard: PN-EN : 2011 Światło i oświetlenie. Oświetlenie miejsc pracy. Valid from Obligatory for employers Lighting parameters for different workstations Visual task Visual elements of work Factors influencing on difficulty level Work object measures Luminance of object Contrast between the object and background Time Visual task area- area for visual tasks performance Surrounding area area encompassing task area with minimal width 0,5 m Visual task area Surrounding area

7 Main lighting criteria illuminance Luminance (glares) Colour aspects Day light Illuminance Appropriate for photopic vision Suitable contrast and detail recognition Fitted to User age Vision task Object of work Minimal required illuminance (E) Location/Task Typical recommended level of maintained illuminance (lux) Vision task area [lx] Surrounding area [lx] General offices 500 Computer workstations 500 Factory assembly areas Rough work 300 Medium work 500 Fine work 750 Very fine work Instrument assembly 1,000 Jewellery assembly/repairs 1, E appropriate for vision task area Hospital operating theatres 50, Evenness of illuminance Lighting design Relation between minimal and mean illuminance Vision task area min. 0,7 Surrounding area min. 0,5 41 Surface Work surface Floor Ceiling 42 7

8 10:1 1:3 Luminance and glare assessment To high luminance risk of glares Measuring: Simple: Illuminance + Reflectance factor - measure of the extent to which a surface reflects incident light; expressed as the ratio of incident flux to reflected flux Complex: UGR (Unified Glare Rating) - The lower the UGR value, the lower the glare Typical relative illuminance values together with suggested reflectance values Maximal contrasts in vision field Contrast - a measure of the difference of luminance levels between two areas 10: Direct and indirect glare Reflection Indirect glare Direct glare Reflection from a mirror: Normal Incident ray Angle of incidence Angle of reflection Reflected ray 47 Mirror 8

9 Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Vision decrease by different angles of luminaires layout Vision decrease Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions 50 Proper layout of luminaires CRI (R a ) Colour Rendering Index A measure of the quality of color light Quantitative measure of the ability of a light source to reproduce the colours of various objects faithfully in comparison with an ideal or natural light source CRI (R a ) Colour Rendering Index For office work R a > 80 For other visual tasks R a > 60 Colour temperature of a light source [K] defined in comparison with a black body radiator and plotted on what is known as the Planckian curve

10 Colour temperature differences 2700K 4000K 6500K Higher colour temperature colder colour of light Influence on thermal comfort Ripple small unwanted residual periodic variation of the direct current (dc) output of a power supply which has been derived from an alternating current (ac) source It caused the stroboscopic effect deceptive immobility of moving objects Ripple reduction 57 10