The Helmholtz-Kohlrausch effect is the influence of color purity on the perceived brightness of a surface. In the following are spectral characteristics of stimuli given that have proven to attract attention equally strong. The high spectral purity that colored LED sources can provide induces the perception of considerable brightness. To test conspicuity a chromatic light patch on a wall was compared to an achromatic one. Below are the profiles given for blue, green, red and purple stimuli that demonstrate equal conspicuity measures than a white spot with a luminance of 10.1 cd/m².

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In this new series light sources, surface characteristics and visual stimuli are characterized by unified profiles. Information about unified profiles to describe spectral data you can find here.

Below two phosphor-converted white LEDs are compared. Light with a Correlated Color Temperature of 4000K causes usually a more cool and bluish impression than light with a CCT of 3000K.

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For wayfinding signage it is essential that the sign is conspicuous and that the messages it contains are legible. This study investigated the optimal luminance for internally lit wayfinding signs in Swiss railway stations. The results demonstrated first, that increasing the light output of the LEDs inside the sign improved conspicuousness of the signage against its surroundings, and second, that considerable improvement of the signage’s legibility could only be observed until its white text reached a luminance of 100 cd/m². Hence, for internally illuminated signage in general indoor situations, a luminance of 100 cd/m² is recommended. Very high luminances should be avoided because even if conspicuity is improved, legibility might worsen.