Evaluation of light sources through the uniques hues and a new multisensory semantic differential

DA POS OSVALDO; PIETTO MARCOS LUIS

Roma

Conferencia; VII Conferenza Nazionale del Colore; 2011

GRUPPO DEL COLORE - ASSOCIAZIONE ITALIANA COLORE

Although illumination is not the centre of our normal visual attention, it has relevant influences both on colour perception and on the feelings of the observers. Here we use two relatively new methods for determining the power of artificial light sources in triggering suitable colours and conveying specific meanings. The determination of unique hues by the observers seems to be a new and very useful methodology for typifying the colour rendition of light sources. Moreover the semantic differential can reveal unexpected characteristics of the illumination otherwise concealed. Traditionally in research with the semantic differential one uses verbal terms, often in opposing pairs (called bipolar scales, for instance: "elegant - dowdy") and the task is to evaluate how much the object under examination can be associated with the characteristics expressed by the scale by placing it in a point of the interval which corresponds to the amount of associability with the two extremes; or else one uses single verbal terms as two terms hardly are exactly opposed (unipolar scale, for instance: "elegant"), and in this case the evaluation can vary from maximum to zero. The novelty of our method is the use of multisensory scales to evaluate the different illuminations. Specifically we used visual, tactile, gustatory, auditory, haptic, and verbal as well, bipolar stimuli (13 in all) for the semantic differential, and four series of coloured cylinders (highly chromatic unique hues) The first task of 18 observers was to chose the unique hue from four series of six coloured cylinders well scaled in hue (NCS highly chromatic yellow, red, blue, and green), under six light sources in a white viewing booth. The second task was the execution of the semantic differential for each light source. Results from the unique hue task show that there is no significant difference due to the different illuminations used in this experiment. Nevertheless unique Yellow is significantly different under the fluorescent and the LED sources. Moreover the unique blue chosen by the observers (S-2065 R90B) consistently differ from the unique blue of the NCS Atlas (S-1565 B; 2nd edition). Results from semantic differential show that the light sources differing in CCT are significantly differentiated (F2,20= 7.394, p < 0.004); the LED 4000K source is differently evaluated from the others, except the fluorescent 6500K (t2,34 ≈ 2.80, p < 0.05); the fluorescent sources are discriminated from the LEDs by a single visual scale (the fluorescent lamps are judged more ´orange´, t12,120 =3.32, p< 0.001); highly significant interactions between illuminations of different CCT and scales are found (F24,240 = 7,1; p = 0,0000). This latter result, strengthened by a factorial analysis, not only shows the great potentialities of the new s.d. method for differentiating light sources, but is also very relevant in highlighting the qualitative aspects which characterize and differentiate the various illuminations.