LIGHT & COLOR. Thoughts on Color

Transcription

1 LIGHT & COLOR Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Thoughts on Color I fly on the breeze of my mind and I pour my soul into my pencil. I dream in color, and see the world through a rainbow. Angela, 8th grader The color of the object illuminated partakes of the color of that which illuminates it. Leonardo da Vinci Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Color The characteristic of light by which a human observer can distinguish between two structure-free patches of light of the same size and shape. Illuminating Engineering Society of North America (IESNA) the red patch the orange patch not a very design-oriented definition Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Color Color is what we call our perception of the wavelength characteristics of electromagnetic radiation W. Grondzik R O Y G. B (I) V recently, indigo (like Pluto) has fallen into question/disfavor with scientists potentially making life more difficult for generations of school children Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Color Concepts There are two key color concepts to consider for lighting design (and many sub-concepts): light source color the wavelength distribution from a source; influenced mainly by the source characteristics object color the wavelength distribution from a surface; influenced mainly by the characteristics of the object and the illuminating source same objects; different light sources Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Color Concepts LIGHT SOURCE COLOR with 2 potential VARIABLES: source and eye Source Perceiver Object OBJECT COLOR with 3 potential VARIABLES: source, object, eye Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Light Source Color involves two potential* variables 1 2 Source Perceiver quantitative qualitative 1. Wavelengths from the source = light source color 2. Impression of wavelengths from the source = perceived light source color * if a neutral observer is assumed, perceiver bias can be removed from consideration and light source color (one variable) can be assumed Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Light Source Color Light source color the wavelengths of light emitted by a source Perceived light source color the wavelengths an observer perceives to belong to a source The (potential) difference between these two concepts is the effect of the individual eye/brain often via color adaptation, but possibly via color blindness see: colourperception.html for a demo of color perception Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Light Source Color Descriptors several ways to name, specify, describe light source color Color Names Color Temperature Correlated Color Temperature Color Rendering Index (CRI) Chromaticity Coordinates Spectral Distribution Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Color Names examples include Warm White, Cool White, Daylight, Deluxe Warm White, All such names are more qualitative than quantitative They are more sales-pitch than science There is no regulation of such names But, they are potentially useful for getting in the right vicinity Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Color Temperature is defined as the absolute temperature of a blackbody radiator having a chromaticity equal to that of a given light source (wow!) -- Expressed in deg K -- Applies only to incandescent sources -- Commonly used in photography Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Some Color Temperatures note the wide range of color temperatures for daylight Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Correlated Color Temperature is defined as the absolute temperature of a blackbody radiator whose chromaticity most nearly resembles that of a given light source -- Expressed in deg K -- Applies to non-incandescent lamps -- Commonly used for fluorescent lamps color temps correlated color temperatures Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Correlated Color Temperatures some examples of correlated color temperature values for fluorescent lamps (Sylvania data): Deluxe Warm White 2950 K Warm White 3000 K Deluxe Cool White 4100 K Daylight (lamp) 6500 K as suggested above, lower color temperatures are perceived as warm and higher temperatures as cool (an interesting grammatical reversal) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Color Rendering Index (CRI) CRI is a measure of the degree of color shift that an object undergoes when illuminated by a given light source compared to the same object illuminated by a reference source of comparable color temperature Expressed as an integer number Low CRI is bad and high is good Commonly used for comparison of light sources same person and clothing different light sources Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Some Typical Color Rendering Index (CRI) Values from IESNA Lighting Handbook; note the wide range of values that may be encountered in/around buildings Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 Chromaticity Coordinates these coordinates represent the ratios of the tri-stimulus values (red, green, blue) relative to the whole of the stimulus value of a color Expressed as decimal numbers Noted as x, y, and z values (usually only 2 of the 3 are explicitly stated) x + y + z = 1.0 Can be measured (although not cheaply) Used where color specification is critical tri-stimulus refers to the current theory that there are three different cone cell types which process red, green, and blue wavelengths Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 chromaticity diagram Chromaticity Coordinates white light is a fairly even mix of red, green, and blue wavelengths (highlighted on the diagram) red, green, and blue represent the tri-stimulus values (corresponding to three distinct types of retinal cones) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Spectral Distribution Graphs these are graphic plots of relative energy content versus wavelength for a specific light source Provide a definitive color descriptor The equivalent of a spectral fingerprint Available from lamp manufacturers Requires a spectrometer to measure (done in a lab setting) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Spectral Distribution Examples sodium vapor deluxe sodium vapor incandescent incandescent has a continuous spectrum like daylight Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Spectral Distribution Examples clear mercury vapor deluxe mercury vapor warm deluxe mercury vapor note the non-continuous nature of these spectra Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 1 source quantitative 2 object Object Color involves three potential variables quantitative qualitative 1. Wavelengths from the source = light source color 2. Selective reflection of source wavelengths from the object = object color (but wait, see next slide) 3. Impression of wavelengths from the object = perceived object color 3 perceiver Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 Object Color Distinctions Object color -- the color of the light reflected or transmitted by an object when illuminated by a standard light source (unfortunately no standard source has been established for design, but let s call it incandescent) Perceived object color (1) -- the color of the light reflected or transmitted by an object when illuminated by a non-standard light source (for example, a sodium vapor or clear mercury lamp) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Object Color Distinctions Perceived object color (2) -- the color of the light that appears to be reflected or transmitted by an object when illuminated by a standard light source as seen by noncolor-neutral viewer as a designer, consider that the colors that people think they see is only statistically predictable Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Object Color Descriptors Color names As with light sources, these are arbitrary and often vague although still useful Color classification schemes Structured and standardized ways to specify object color Chromaticity coordinates Same concept as used for light sources Spectral distribution plots Same concept as used for light sources Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Color Names creative, yet arbitrary and often proprietary (company-specific) descriptions Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 Color Classification Schemes the Munsell system (there are other systems) permits generic, non-proprietary specification of colors although the system itself is proprietary Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Color Classification Schemes in the Munsell system each color has three characteristics hue ( color ) value (lightness) chroma (strength) combinations of these three variables define a specific color Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

15 Color Relationships mixing light sources: is an additive process (such mixing increases the array of wavelengths) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Color Relationships mixing pigments on objects is a subtractive process (it decreases the reflected wavelength composition as each color absorbs a different part of the spectrum) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15

16 Color and Design a discussion of color and design will best occur in studio but the issue is critical to occupant/user perceptions and responses and is greatly affected by lighting system design choices some design color schemes >> achromatic; monochromatic; analogous complementary; split complementary, triad Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 Major Lighting Organizations Illuminating Engineering Society of North America (IESNA) -- a big-umbrella organization (includes engineers, architects, manufacturers) -- publishes the IESNA Lighting Handbook International Association of Lighting Designers (IALD) -- influential, less technical than IESNA National Lighting Bureau -- an applications (results) based organization Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32 16