These teachings relate generally to luminous systems that provide observed visible color, and more particularly to a luminous system that provides a first observed visible color that is primarily produced by the emission of the system when such system is powered, and also provides a second observed visible color that is primarily produced by the reflection of the system when such system is non-powered.
The primary purpose of luminous systems is to generate light of certain desired visible color(s), white, blue, green, etc., with the use of illumination source(s), e.g. LEDs, for a broad range of applications, e.g. general lighting, illuminated graphics, etc. Thus, when the illumination source(s) are powered, the observed visible color of such systems is predominantly a result of the emission produced by the system. However, when the illumination sources are non-powered, the observed visible color of such systems is mainly produced by way of ambient light reflected from the surface of the system, e.g. a luminous system having a white surface will reflect ambient light that is observed as a white visible color, whereas a luminous system having a red surface will reflect ambient light that is observed as a red visible color.
In general, white illumination sources, including white light LEDs, have been used in luminous systems to generate light of observed visible color, e.g. white light or colored light. In instances where colored light is desired, these systems generate color through the absorption of all the wavelengths of light produced from the white illumination source(s), except those wavelengths associated with the color desired. Unfortunately, this approach to color generation results in substantial loss of energy due firstly, to the amount of energy needed to create the white light, and secondly, to the additional energy lost in the subtraction of the wavelengths to create a colored emission. This can be a particular problem when the white illumination source does not contain sufficient energy of the desired color, such as for example in the case of white light LEDs that provide only modest amounts of energy at red wavelengths. An additional drawback to utilizing white illumination sources is the difficulty in manipulation of the reflected light of the system, therefore suffering from the limitation that the observed visible color produced when the white illumination sources are non-powered must be substantially the same as the observed color when the illumination sources are powered. This is due to the color generation mechanism of the system since wavelengths associated with that of the white illumination source are similar to those associated with the ambient light, therefore making it difficult to tailor the emission of the system without affecting the reflection of the system and vice versa.
In an effort to provide more efficient luminous systems, UV or blue illumination sources have been utilized, rather than white, to generate light of visible color, e.g. white light or colored light. This is generally accomplished by down-converting the emission energy of the UV or blue illumination source(s) into longer wavelengths with the use of energy converting material(s), e.g. phosphorescent and/or fluorescent materials. For example, when a blue LED is used as the illumination source to provide the primary electromagnetic radiation, the luminous system can generate white light by absorbing a portion of the primary electromagnetic radiation, i.e. blue light in this case, using a energy conversion layer and down-converting this radiation to a secondary electromagnetic radiation having green and yellow wavelengths, thereby resulting in an emission of the system comprising blue, green and yellow wavelengths which produce an observed visible color of white. Although these systems may be more efficient in generating light than those which utilize white light sources, when these systems are non-powered, the observed visible color of the system is also difficult to tailor to a desired observed visible color. However, with the use of UV or blue illumination source(s) along with energy converting material(s), the observed visible color of the system when the UV or blue illumination source(s) are non-powered is now not only the unabsorbed ambient light that is reflected from the surface of the system, but also the emission of the energy conversion material(s), although minimal, due to the system's exposure to ambient light. For example, the absorption of blue light by the energy conversion layer causes the reflectance of the surface of the system to appear yellowish when the primary electromagnetic radiation is not supplied, i.e. the illumination source(s) are non-powered, resulting in an undesirable observed visible color.
There is, therefore, a need for utilizing higher efficiency luminous systems which are capable of not only providing a desired observed visible color when powered, but also a desired observed visible color when non-powered. It is also desirable to provide higher efficiency luminous systems, wherein the system not only embodies elements for achieving desired observed visible color when powered and when non-powered, but also embodies elements that enable the system to provide a wider gamut of observed visible color without substantial loss of energy. Furthermore, it is also desirable to incorporate within these systems elements that enable the luminous system to not only generate light of observed visible color, but also for a broad surface area.