AQUARIUM LIGHTING

Abstract: A fluorescent lamp for use in aquaria, the luminescent layer in said lamp comprising a mixture of red, green and blue phosphors, the red phosphor emitting predominantly in the spectral region of from 610 nm to 620 nm, the green phosphor emitting predominantly in the spectral region of from 540 nm to 545 nm and the blue phosphor having a peak emission wavelength between 430 nm and 480 nm with the half peak width not exceeding 80 nm, said red, green and blue phosphors being blended to form said mixture in such proportions that the colour co-ordinates of the lamp employing said mixture on the CIE chromaticity diagram differ from the point x equals 0.300 and y equals 0.232 in any direction by no more than 10 standard deviations of colour matching (SDCM). Aquaria employing such lamps are also disclosed and claimed.

Description: This invention relates to aquarium lighting and, in particular to a fluorescent lamp for use in aquaria. Aquaria, particularly the relatively small type for household use are commonly lit with fluorescent lamps. The type of fluorescent lamp most commonly used, whilst imparting a not unattractive reddish colour to orangy objects, such as goldfish, suffers from the disadvantage that, since a reddish cast is also imparted to almost all colours, the many and varied varieties of fish now popular for small aquaria do not show up to best advantage. Further disadvantages of this lamp include low lumen output, poor lumen maintenance and a large colour drift with age affecting both lamp appearance and colour rendering. EP-A-0228010 discloses a low-cost luminescent phosphor which is formed by sintering a phosphor with an alkaline earth metal sulphate. In one particular fluorescent lamp, the fluorescent layer contains blue, green and red-emitting materials, at least one of which has this sintered composition. The three colour emitting materials have peak emission wavelengths within the ranges 430-475, 520-560 and 595-630nm, respectively. It is an object of the present invention to provide an improved fluorescent lamp for use in aquaria, particularly tropical marine aquaria. Accordingly, we provide a fluorescent lamp for use in aquaria, the luminescent layer in said lamp comprising a mixture of red, green and blue phosphors, the red phosphor emitting predominantly in the spectral region of from 610 nm to 620 nm, the green phosphor emitting predominantly in the spectral region of from 540 nm to 545 nm and the blue phosphor having a peak emission wavelength between 430 nm and 480 nm with the half peak width not exceeding 80 nm, said red, green and blue phosphors being blended to form said mixture in such proportions that the colour co-ordinates of the lamp employing said mixture on the CIE chromaticity diagram differ from the point x equals 0.300 and y equals 0.232 in any direction by no more than 10 standard deviations of colour matching (SDCM). Most preferably, the lamp of our invention has the colour co-ordinates x equals 0.300 and y equals 0.232. Individual red, green and blue phosphors which may be used to form the above mixture are well known in the art and we have found that suitable such phosphors include the following:- Red phosphor Yttrium and/or gadolinium oxides activated by trivalent europium and having the following formula: (Y a Gd 1-a )₂O₃ : Eu³⁺ In the preferred case a is 1, i.e. the phosphor is:- Y₂O₃ : Eu³⁺ Green Phosphor Cerium and terbium activated aluminates, silicates, phosphates and borates selected from compounds of the following formulae:- CeMg Al₁₁O₁₉ : Tb Y₂SiO₅ : Ce, Tb LaPO₄ : Ce,Tb LaMgB₅O₁₀ : Ce, Tb Particularly suitable are: CeMgAl₁₁O₁₉ : Tb and LaPO₄ : Ce, Tb Blue Phosphor Alkaline earth hexagonal aluminates of the B-alumina structure, or alkaline earth chlorophosphates, each activated by divalent europium and having the following formulae:- BaMgAl₁₀O₁₇ : Eu²⁺ BaMg 1.7 Al₂₀O 32.7 : Eu²⁺ BaMg₂Al₂₄O₃₉ : Eu²⁺ (Sr,Ca,Ba)₁₀Cl₂(PO₄)₆ : Eu²⁺ As stated above, in order to produce the mixture for use in the luminescent layer of the lamp of the present invention, it is necessary to blend the three selected phosphors in such proportions that the lamp has the desired colour co-ordinates. The procedure for producing the correct blend is well known to experts in the art and the specific example set out hereinafter describes this more particularly. Those skilled in the art will readily appreciate that since there are many factors other than weight proportions which affect the contribution of each phosphor in a mixture to the colour of a lamp employing a phosphor layer comprising such a mixture it is not meaningful to lay down a particular weight proportion for each component of the mixture which will result, in all cases, in a lamp having the desired colour co-ordinates. These rather factors, which cause the required weight properties to vary, include (among other possible ones) particle size profiles of the component phosphors, relative efficacies of the component phosphors, relative bulk densities of the component phosphors, size and loading of lamp using the phosphor mixture. In the attached Figure 1a there is reproduced the CIE chromaticity diagram in which is marked the point A which has the co-ordinates x = 0.300 and y = 0.232. Also shown in the form of an elipse centred on A is the area covering all points in any direction within 10 SDCM of the point A. The nature of this 10 SDCM elipse can be more clearly seen on Figure 1b which is an enlargement of the relevant portion of the CIE chromaticity diagram. It will be seen that the point A is in a significantly different position on the diagram from that occupied by the co-ordinates of a lamp which prior to this invention was commonly used in aquaria and which are shown by point B on the CIE diagram of Figure 1a. The invention may be illustrated by the following example:- Example A mixture of phosphors was prepared from the following three materials:- a) Red Phosphor Yttrium oxide activated with trivalent europium as commercially supplied by Elgar Phosphors & Chemicals Ltd., Lincoln Road, Enfield, Middlesex, under the code number 2005. This material, when illuminated by the ultraviolet light produced in a low pressure mercury vapour discharge such as occurs in known fluorescent lamps emits predominantly in the spectral region of from 610nm to 620nm [see spectrum in accompanying Figure 2a]. b) Green Phosphor Magnesium aluminate activated by cerium and terbium of the formula; CeMgAl₁₁O₁₉ : Tb and as commercially supplied also by Elgar Phosphors & Chemicals Ltd. under the code number 3003. This material, when illuminated by ultraviolet light (as above) emits predominantly in the spectral region of from 540nm to 545nm (see spectrum in accompanying Figure 2b]. c) Blue Phosphor A barium magnesium aluminate activated with divalent europium of the formula:- BaMg 1.7 Al₂₀O 32.7 : Eu²⁺ as commercially supplied also by Elgar Phosphors & Chemicals Ltd. under the code number 4001. This material, when illuminated by ultraviolet light as above exhibits peak emission at a wavelength, [as can be seen from the spectrum in Figure 2c], in the range of 430 nm to 480 nm and has a half peak width of 50 nm. The mixture of phosphors contained the following proportions by weight of the above phosphors: red phosphor : 37% green phosphor : 19% blue phosphor : 44% The said mixture was coated onto the inside surface of a glass tube of 38.1 mm (1.5 inch) diameter and 1.22 m (4feet) in length which was then used to produce a 40w fluorescent lamp. This lamp had the co-ordinates on the CIE chromaticity diagram of x equals 0.300 and y equals 0.232. The lamp also had an output of 2000 lumens (cf. 1100 lumens for the corresponding lamp previously used in aquaria). After 2000 hours in use the lamp had a lumen output equal to 95% of its initial lumen output and showed only minor colour drift (less than 3 SDCM). This compares with a lumen maintenance of the lamp most commonly previously based in aquaria of 82% after 2000 hours, and a large colour drift. As will be appreciated from the above specific example, this invention provides aquarium lighting which has improved lumen output and maintenance and exhibits only minor colour drift. In addition to this it provides a very pleasing subjective effect. There is a marked absence of the reddish cast which the previously commonly based lamp types imparted to almost all colours and it is thus possible for the viewer to appreciate all the many and varied colours of the fish, coral, algae and other objects commonly included in an aquarium, whether of the cold freshwater, tropical freshwater or tropical marine type. It has further been shown that the lamps of this invention when used over tropical marine aquaria are particularly suitable for the invertebrates such as coral and algae whose individual and symbiotic growth are supported by the lamps. In practical lighting experiments carried out in marine aquaria containing a selection of light dependent marine invertebrates (e.g. mushroom corals, goniapora, anemones and clams) and micro/macro algae (e.g. Caulerpa sp.), four 20w lamps of this invention gave a substantially higher intensity of illumination, stimulated algal growth and promoted coral health and well being noticably better than the best previously known illumination comprising an elaborate combination of four existing commercially available 20w lamps comprising a 'Grolux' lamp, two 'North Light' lamps and a deep blue lamp. Such a combination is difficult to adjust properly and not easily available to the average home aquarium owner. Our invention, in contrast, provides illumination from a single lamp type which will give at least as good results and avoids these disadvantages.

Claims: A fluorescent lamp for use in aquaria, the luminescent layer in said lamp comprising a mixture of red, green and blue phosphors, the red phosphor emitting predominantly in the spectral region of from 610 nm to 620 nm, the green phosphor emitting predominantly in the spectral region of from 540 nm to 545 nm and the blue phosphor having a peak emission wavelength between 430 nm and 480 nm with the half peak width not exceeding 80 nm, said red, green and blue phosphors being blended to form said mixture in such proportions that the colour co-ordinates of the lamp employing said mixture on the CIE chromaticity diagram differ from the point x equals 0.300 and y equals 0.232 in any direction by no more than 10 standard deviations of colour matching (SDCM). A fluorescent lamp according to Claim 1 which has the colour co-ordinates x equals 0.300 and y equals 0.232. A fluorescent lamp according to Claim 1 or Claim 2 wherein the red phoshpor is an yttrium and/or gadolinium oxide activated by trivalent europium and having the following formula: (Y a Gd 1-a )₂O₃ : Eu³⁺ wherein a is equal to or less than one. A fluorescent lamp according to Claim 3 wherein a is one. A fluorescent lamp according to any one of the preceding claims wherein the green phosphor is a cerium or terbium activated aluminate, silicate, phosphate or borate selected from compounds of the following formulae:- CeMg Al₁₁O₁₉ : Tb Y₂SiO₅ : Ce, Tb LaPO₄ : Ce,Tb LaMgB₅O₁₀ : Ce, Tb A fluorescent lamp according to Claim 5 wherein the green phosphor is a compound of the formula CeMg Al₁₁O₁₉ : Tb or LaPO₄ : Ce,Tb A fluorescent lamp according to any one of the preceding claims wherein the blue phoshor is an alkaline earth hexagonal aluminate of the B-alumina structure, or an alkaline earth chlorophosphate, each activated by divalent europium and having the following formulae:- BaMgAl₁₀O₁₇ : Eu²⁺ BaMg 1.7 Al₂₀O 32.7 : Eu²⁺ BaMg₂Al₂₄O₃₉ : Eu²⁺ (Sr,Ca,Ba)₁₀Cl₂(PO₄)₆ : Eu²⁺ A fluorescent lamp according to Claim 1 wherein the red phosphor is yttrium oxide activated with trivalent europium, the green phosphor is of the formula CeMg Al₁₁O₁₉ : Tb and the blue phosphor is of the formula BaMg 1.7 Al₂₀O 32.7 : Eu²⁺ A tropical marine aquarium provided with one or more fluorescent lamps according to any one of the preceding claims.

Inventors: ABEYWICKRAMA, MILROY GAMANI, NEWMAN, BARRY JOHN
Applicants: THORN EMI PLC
Application year: 1989
Main classification: H01J61
IPC codes: A01K63, C09K11, H01J61