GB2228561A

GB2228561A - Variable colour light

Info

Publication number: GB2228561A
Application number: GB8826216A
Authority: GB
Inventors: Stuart Patrick Richards
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-11-09
Filing date: 1988-11-09
Publication date: 1990-08-29
Also published as: GB8826216D0

Abstract

A variable colour light filter comprises a filter screen 4 having a plurality of coloured sections, each section being of one colour; a masking member having a plurality of opaque sections so sized and shaped that, in use, the masking member 5 masks part, but not all, of the screen; and means 8 diffusing the light which passes, in use, through the unmasked part of the screen; the screen and the masking member being movably mounted with respect to one another, and the arrangement being such that the colour of the light passing through the filter may be varied by altering the relative position of the masking member and the screen. <IMAGE>

Description

VARIABLE COLOUR LIGHT Background to the Invention The invention relates to a device for producing diffused light, the colour of which may be varied, and is more particularly concerned with a variable colour filter for use in such a device.

The principal factor determining the colour of emitted light is the wave length of the light. However, using the additive light principle, it is possible to simulate the emission of light of practically any colour within the visible spectrum by appropriately combining light of any two or more . of the three primary colours: red, green and blue.

For example, if appropriate intensities of red and green are combined, yellow light will be seen, despite the fact that no light of a wave length corresponding to orange is being emitted.

In the context of this specification, the colour of light is taken to include the perceived colour of a combination of light of other colours, and the term variable colour should be construed accordingly.

Devices for producing light of a variable colour are known.

An example of such a device is shown in Czechoslovakian patent specification No 213 578.

Summary of the Invention According to the invention, there is provided a variable colour light filter comprising a filter screen having a plurality of coloured sections, each section being of one colour; a masking member having a plurality of opaque sections so sized and shaped that, in use, the masking member masks part, but not all, of the screen; and means diffusing the light which passes, in use, through the unmasked part of the screen; the screen and the masking member being moveably mounted with respect to one another, and the arrangement being such that the colour of the light passing through the filter may be varied by altering the varied position of the masking member and the screen.

With the filter positioned in front of a white light source, each coloured section will, when unmasked, transmit light of- the same, or predominantly the same, colour as that of the section. If light of two or more colours is transmitted from the unmasked part of the screen, the diffusing means will combine the colours, and the additive light principle will apply.

The relative intensities of the colours of the transmitted light may be varied by partially masking or unmasking the correspondingly coloured sections on the screen with the masking member. Thus, by moving the screen and the masking member relatives to one another, the colour of the diffused light may be varied.

The diffusing means may comprise any suitable light scattering material such as, for example, a translucent perspex sheet through which, in use, the light passes.

The screen preferably includes a red section, a green section and a blue section; and the relative position, sizes and shapes of the opaque sections of the masking member so correspond to the sections of the screen that, by appropriately aligning the screen and the masking member, all sections of any one of the colours red, blue and green may be masked.

In this case, the screen may, with advantage, include a plurality of red sections, a plurality of green sections and a plurality of blue sections. This feature enables the diffusing means to produce a more evenly diffused pattern of light of a relatively large area.

Each section of the screen may be contained within the sector of a circle. In this case, the masking member and the screen may be mounted for relative rotational movement about an axis passing through or near the centre of the circle, and being perpendicular to the circle.

Alternatively, the sections of the screen may be formed as a series of parallel strips, and the screen and the masking member may be mounted for relative translational motion perpendicular to the stips.

Another version of the screen has coloured sections formed as an array of rows of squares, the corresponding adjacent squares in adjacent rows being relatively longitudinally displaced by one half of one square. In this case, the opaque sections of the masking member are arranged in a tchequered" pattern.

The filter may be placed in front of a light source to provide a variable colour light.

Brief Description of the Drawings The invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a schematic sectional side view of a filter according to the invention when placed in front of a light source; Figure 2 is a plan view of the filter screen of the filter shown in figure 1; Figure 3 is a plan view of the masking member of the filter of figure 1; Figure 4 shows an alternative form of filter screen; Figure 5 shows a masking member for use with the filter screen shown -in figure 4; Figures 6 and 7 respectively show another form of filter screen, and its associated masking member; Figures 8 and 9 show a mechanism for moving the screen of figure 4 relative to the masking member of figure 5; and Figure 10 shows an alternative of blanking screen for use with the filter shown in figure 1.

Description of an embodiment Referring to figure 1, a parallelepipedal casing 1 is open at one end, and houses a flourescent lamp 2. An example of one kind of lamp which may be used is that sold in the United Kingdom by Thorn EMI under the trading style 2D. This kind of lamp, in use, in its light of a number of colours including red, blue and green, whilst generating relatively little heat.

Reflective materials (not shown) are so mounted on the inner surfaces of the casing 1 as to maximise, in use, the intensity of the light travelling towards the open end of the casing 1. A translucent screen 3 is interposed between the light source 2 and the open end of the casing 1, and acts as an initial diffuser which, together with the reflected materials, more evenly distributes the light emitted, in use, by the lamp 2.

A filter screen 4 is mounted towards the open end of the casing 1. As can be seen from figure 2, the filter screen 4 includes a number -of sections formed as a series of parallel strips of colour filters, each section being one strip. A first section 4a is coloured red, and thus, in use, allows only predominantly red light to pass through it. A second section -4b is coloured blue, and a third section 4c is coloured green.

The sequence then repeats itself so that the screen only contains red, blue and green sections, and that adjacent sections of any one of the three colours are spaced by two sections.

The predominantly red, green and blue light passing, in use, through the filter screen 4 is then incident on a masking member 5 slidably mounted at the open end of the casing 1.

Referring to figure 3 the masking member 5 includes a number of opaque sections, one of which is referenced 6, formed as a series of parallel strips* each opaque section being one strip. The masking member 5 also includes a series of parallel transparent strips, for example strip 7, which alternate with the opaque section. The width of each opaque section is twice that of a coloured section of the screen 4, whilst each transparent section is of approximately the same width as each section of the screen 4.

The masking member is, in use, mounted, with the opaque sections parallel to the sections of the screen 4, in a pair of opposed, parallel tracks (not shown) in the casing one. The tracks allow -sliding movement of the masking member 5 in a direction perpendicular to the sections of the filter screen 4.

The distance between the masking member 5 and the filter screen 4 is small, so that, by appropriately positioning the masking member 5 it is possible to align each of the opaque sections with two sections of the filter screen 4. When so positioned, the masking member 5 will mask all sections of the screen 4 of any two colours, since the sections of the screen 4 are arranged in the same colour sequence over the whole length of the screen.

A translucent sheet 8 is mounted above the masking member 5, and serves to diffuse, in use, the light being transmitted from the unmasked part of the filter screen 4, the portions of the filter screen 4 aligned with the transparent strips of the masking member 5. When in the position just described, the masking member will only allow light of predominantly one colour, for example red, to be transmitted to the sheet 8.

It is also possible to so position the masking member 5 that all sections of the screen 4 of only one colour are masked, in which case the sections of the other two colours will be partially unmasked. This results in light of predominantly two colours being transmitted to the screen 8, which mixes the two colours to give a third colour using the additive light principle.

Thus, by appropriately positioning the screen, the filter may produce not only red, blue and green light, but also light of intermediate colours, for example,rmagenta, yellow and cyan.

The masking member 5 may be moved manually or alternativly by a mechanism which would be apparent to the skilled addressee. An example of such a mechanism would be a "worm gear" acting between the masking member 5 and the casing 1 and driven by an electrical motor.

Figure 4 shows an alternative type of screen in which the sections are formed as an array of squares, each section being one square. The squares are arranged in a series of rows (referenced 9-18 inclusive).

In row 9, the first square 19 is blue, the second square 20 is green and the third square 21 is red. The sequence then repeats itself along the rest of the row 9. In row 18 the first half square 22 is green, the square 23 is red and the square 24 is blue, and the sequence of colours repeats itself along the rest of the row 18.

Rows referenced with an even number are identical to row 18, whilst those referenced with an odd number are identical to row 9. Thus correspondingly coloured adjacent squares in adjacent rows are relatively longitudinally displaced by 1r squares.

Referring to figure 5, the mask for use with this kind of filter screen has a number of opaque sections arranged in a series of rows corresponding to the rows of squares of the filter screen. Each whale opaque section, for example section 25, is a rectangle of twice the length of, and the same width as, a square on the filter screen. In each row, adjacent opaque sections are separated by a transparent section, such as section 26, which Is of the same size as a square on the filter screen.

The opaque sections are arranged in a partially overlapping chequered pattern in which adjacent transparent squares in adjacent rows are relatively longitudinally displaced by 1 squares. As a result, when each opaque section is aligned with two squares in a corresponding row of the filter screen, filter -squares of only one colour will be unmasked. If the masking member is then moved a distance of one half of one filter square in one of the directions indicated by the arrow X, filter squares of only two colours will be partially unmasked.

Thus, with the rows of opaque sections and filter squares aligned, - movement in the one of the directions indicated by the arrow X causes, in use, a variation of colour over the same range as is obtainable with the first kind of mask and filter screen.

Additionally, when the rows of opaque sections are not in alignment with the rows of filter squares, filter squares of all three colours are partially unmasked. This can be achieved by moving the masking member in one of the directions indicated by the arrow Y, and enables white light and intermediate shades, to be produced.

An example of one kind of means which may be used to move the masking screen shown in figure 5 in two perpendicular directions is shown in figures 8 and 9.

The masking screen (referenced 27) is slidably mounted on a sub frame 28. The sub frame 28 is, in turn, slidably mounted on three supports 29 which are attached to the casing 1.

Two springs 30 act between the masking member 27 and the sub frame 28 to bias the masking member 27 against a cam 31. An electrical motor (not shown) is operable to rotate the cam, and thus, in conjunction with the springs 30, to move the masking member 27 in either direction indicated by the arrow X.

Movement of the sub frame 28, and hence the masking member 27, in either direction indicated by the arrow Y is achieved in a similar way using two springs 32 acting between the sub frame 28 and the casing 1 and a motor driven cam 33.

Referring to figure 6, the sections of a third kind of filter screen 34 are formed as the sectors of a circle.

Each sector is on section, and all the sectors are of the same angular size.

A first section 35 is red, a second section 36 is green and a third section 37 is blue. This colour sequence then repeats itself around the rest of the circle so that, in total, the circle contains 8 sections of each colour.

The opaque sections of the corresponding masking member 38 (figure 7) are also formed as the sectors of a circle.

Each opaque section is of twice the angular size of a filter section and adjacent opaque sections are separated by a transparent section, for example section 39, which is of the same angular size as a filter section.

The filter screen 34 and the mask 38 are, in use, concentrically mounted, and the mask 38 may be rotated about an axis passing through the centre of the two circles.

The mask 38 may be rotated manually or by an electric motor, the output shaft of which is directly connected to the centre of the masking member 38.

Instead of producing light of a relatively uniform colour, the filter may be modified, so that, in use a pattern of colours appears on the screen 8. If, for example, the masking member shown in figure 10 is used with the filter screen of figure 2, a series of bands of gradually changing colours would, in use, appear on the screen 8.

The filter screen, the masking member and the diffusing screen may alternatively comprise a series of substantially concentric cylinders which, in use, surround a light source.

It is possible for the masking member to be interposed between the filter screen and the light source. In this case the underside of the masking member may be coated with a suitable reflective material to optimise the efficiency of the filter.

Although the filter screens just described have only red, green and blue sections, it is possible to use other colours as primary colours if, for example, the chosen primary colours were magenta, cyan and yellow, the additive light principal would still apply.

Claims

CLAIMS:

1. A variable colour light filter comprising a filter screen having a plurality coloured sections, each section being of one colour ; a masking member having a plurality of opaque sections so sized and shaped that, in use, the masking member masks part, but not all, of the screen; and means diffusing the light which passes, in use, through the unmasked part of the screen; the screen and the masking member being moveably mounted with respect to one another, and the aFrangement being such that the colour of the light passing through the filter may be varied by altering the relative position of the masking member and the screen.

2. A variable colour filter according to claim 1 in which the screen includes a red section, a green section and a blue section ; and in which the relative position, sizes and shapes of the opaque sections of the masking member so correspond to the sections of the screen that, by appropriately aligning the screen and the masking member, all sections of any one or more of the colours red, blue and green may be masked.

3. A filter according to claim 2 in which the screen includes a plurality of red sections, a plurality of green sections and a plurality of blue sections.

4. A filter according to any of the preceding claims in which each section of the screen is contained within the sector of a circle; and in which the masking member and the screen are mounted for relative rotational movement about an axis passing through or near the centre of the circle and perpendicular to the circle.

5. A filter according to any of claims 1 to 3 in which the sections of the screen are formed as a series of parallel strips; and in which the screen and the masking member are mounted - for relative translational motion perpendicular to the, Strips.

6. A filter according to any of claims 1 two 3 in which the sections of the screen are formed as an array of rows -of squares, the corresponding adjacent squares in adjacent rows being relatively longitudinally displaced by one and one half squares;. and in which the opaque sections of the masking member are arranged in a "chequered" pattern.

7. A variable colour light comprising a light source situated adjacent a filter according to any of the preceding claims.

8. A variable colour filter substantially as described herein with reference to the accompanying drawings.