OF FLUORESCENT OBJECTS

The present invention relates to a method for compensating for colour when illuminating fluorescent objects that fluoresce when illuminated with ultraviolet light.

The objects concerned may be of diverse kinds, such as different signs that have different functions, road markers, sea markers, etc. Flags are objects of primary interest.

Swedish Patent Specification No. 9200250-0 relates to a method for illuminating flags hoisted on flag poles, particularly advertising flags of the kind that are placed along automobile routes in the vicinity of restaurants, hotels, gas filling stations. The invention defined in this patent specification is characterized by illuminating one or more flags which include ultralight fluorescent material by means of one or more illuminating lamps which emit a significant percentage of ultraviolet light.

Such flags are used to a large extent to mark the presence of hotels, filling stations, restaurants, etc. , among other things. Often there is a desire to amplify the effect by placing a number of flags adjacent to one another, and often on relatively high flag poles. The intention is to draw the attention of motorists to the presence of a filling station or a rest station in good time before the motorist reaches the particular station concerned. Such flags can be seen relatively well in the daylight hours. The flags are relatively normally illuminated by illuminating lamps during the darker hours of the day. The illuminating effect is restricted by the fact that the flags normally take-up only a small part of the light cone of the lamps, therewith illuminating the flags only to a limited extent.

The flags are made visible to a very great extent when illuminated with ultraviolet light, therewith enabling the flags to be seen much more clearly during the dark hours of the day.

A very large part of flags of this nature, such as adver¬ tising flags, are often white in colour, for instance have a white background. It is relatively usual to produce advertising flags and the like from a white fabric on which different trade names and/or text are printed.

One serious problem is that when illuminating fluorescent flags that are comprised of a white fabric, the fluores¬ cence effect obtained is always more blue than white. The same applies to fluorescent white paints, dyes and plas¬ tics.

This problem is mainly due to two things. Lamps that emit ultraviolet light and are capable of being used in practice include a filter which functions to filter-out visible light. Firstly, the filter allows a certain amount of visible blue light to pass through and this light is reflected by the fabric as it impinges thereon. The fabric is therewith seen to be blue by the eye of the viewer. Secondly, white fluorescent pigment is often comprised of a so-called optical whitening agent which fluoresces in a spectrum that has dominance in the visible blue range.

Consequently, a flag for instance which is intended to be white and which is seen to be white in daylight will no longer be seen as white when illuminated with ultraviolet light during the dark hours, but will be seen as varying degrees of blue. There is a strong desire for flags to be seen as white even when illuminated with ultraviolet light. The same problem is found with objects other than flags.

An object of the present invention is to solve this problem.

Accordingly, the present invention relates to a method of compensating for colour when illuminating fluorescent objects with the aid of one or more illuminating lamps which emit a significant amount of ultraviolet light, particularly when illuminating flags that are hoisted on flag poles, wherein the objects include ultralight fluores- cent material and have a white or light colour when illuminated with visible light, said method being charac¬ terized by including in the object an additional fluores¬ cent material which when illuminated fluoresces in a colour which together with a weak blue colour, said blue colour deriving from illumination of the object with ultraviolet light, will produce a white or essentially white colour by additive colour mixture.

The invention will now be described in more detail with reference to an exemplifying embodiment thereof applied to flags, although it will be understood that the invention is not restricted to flags, but includes all manner of objects.

The present invention relates to a method of colour compensation when illuminating fluorescent objects by means of one or more illuminating lamps which emit a significant amount of ultraviolet light, particularly when illuminating flags that are hoisted on flag poles, said objects includ- ing ultralight fluorescent material and having a white or light colour when illuminated with visible light.

The invention is particularly concerned with advertising flags of the kind that are placed along automobile routes in the vicinity of restaurants, hotels and filling sta¬ tions. The invention, however, can be applied to objects

other than flags, for instance marquees, banderoles, different types of signs or road or sea markers.

Objects with which the invention can be applied are light in colour, i.e. white objects or objects in a light colour. By light colour is meant a colour which is so light that the blue light deriving from illumination of the object with lamps that emit ultraviolet light will be seen with the naked eye.

Even though the aforesaid problem is greatest when the object concerned is white, the problem also occurs with colours other than white. For instance, a light red colour tends to shift to violet as a result of the contribution of the blue light.

According to the invention, the object is caused to include an additional fluorescent material which when illuminated fluoresces in a colour which together with the weak blue colour, said blue colour deriving from the illumination of the object with ultraviolet light, will produce a white or essentially white colour by additive colour mixture.

By additive colour mixture is meant that the weak visible blue light mixes additively with the visible light emitted by the additional fluorescent material.

According to one preferred embodiment of the invention, the additional fluorescent material fluoresces in a yellow colour. This means that the blue light that derives from illuminating the object with ultraviolet light mixes additively with the visible yellow light that derives from the yellow light emitted through fluorescence to a light which is observed to be white by the naked eye.

According to another preferred embodiment of the invention, the additional fluorescent material is colourless or white

when illuminated with visible light. A colourless material will mean that the colour of the object will not be influenced by the additional material when illuminating with visible light. A white additional material is primari- ly intended for objects that are white when illuminated with visible light.

There are commercially available large numbers of fluores¬ cent pigments, both organic and inorganic pigments, which are suitable for use when practicing the invention, irrespective of whether the invention is applied for colour compensation of fabrics, paints or plastics. The person skilled in this art will therefore have no problem in choosing a suitable fluorescent pigment for the additional material according to the invention, and to dose this material so that the light emitted as it fluoresces will compensate the aforesaid blue light.

It can be mentioned by way of example that a material which fluoresces in a yellow colour and which is suitable for compensating the aforesaid blue light when the objects concerned are white flags is manufactured by Hoechst AG in Germany under the designation CD 704, and by Riedel-de-Haen in Germany under the designation CD 404, among other manufacturers.

The additional material can be applied in several conven¬ tional ways. For instance, fabrics can be dipped in a slurry containing the additional material. The additional material may also be printed onto the fabric. With regard to other objects, for instance plastic objects such as signs, the additional material may be admixed with the plastic, as is also the remaining fluorescent material.

The present invention solves the problem mentioned in the introduction, irrespective of whether or not the blue light is derived solely from the lamp that transmits ultraviolet

light, or is derived solely from the fluorescent material that is included in the object to provide the intended fluorescence effect, or is derived from both of these sources.

It will be understood that the present invention is not restricted to the aforedescribed embodiments and that modifications can be made within the scope of the following Claims.