GB2170256A

GB2170256A - Natural-light illumination enhancement assembly

Info

Publication number: GB2170256A
Application number: GB08602134A
Authority: GB
Inventors: Donald Louis Critten; Albert Louis Critten
Original assignee: National Research Development Corp UK
Current assignee: National Research Development Corp UK
Priority date: 1985-01-29
Filing date: 1986-01-29
Publication date: 1986-07-30
Also published as: GB8502150D0; GB8602134D0; GB2170256B

Abstract

A natural light enhancement assembly (Fig. 3) of prismatically-profiled sheets of which sheets 1 redirect the incident light forwardly by refraction and the remaining sheets 2 redirect the incident light rearwardly by internal reflection. Each sheet comprises transparent or translucent material profiled so as in cross-section to present a series of projections, light receiving surfaces of which are all inclined to the mid- plane of the sheet at an angle of between about 30 DEG and 60 DEG . The walls of the prismatic projection may be convex (Fig. 4). <IMAGE>

Description

SPECIFICATION Natural-light illumination enhancement assembly The present invention relates to an assembly for enhancing greenhouse or factory illumination using natural light.

In the past attempts at enhancing greenhouse illumination, a fully reflecting north wall has been provided to direct back on to the house floor sunlight which would otherwise have passed out through the north wall. Such an arrangement suffers from a number of disadvantages. For example, the illumination may not extend over the entire house floor; tall crops can obscure the reflecting surface; and, unless the reflector can be removed, significant losses will occur under diffuse overcast conditions due to the obscuration of the north sky by the north wall of the house.

In an attempt to provide a natural-light illumination enhancement assembly in which the above disadvantages are overcome or at least significantly reduced, UK Patent Application 8316511 (NRDC) discloses a natural-light illumination enhancement assembly in which an array of wholly or partially reflecting louvres is suspended so that natural light which otherwise would not fall on crop in the greenhouse is reflected on to it by the assembly. Typically, the assembly would be suspended from the highest point of a single-span greenhouse or along the north or most northerly side of the greenhouse.

A somewhat similar proposal is contained in GB 1148677 (Talium AG) where an array of specially made slat-form or prism-form louvres is used to improve daylight illumination in a domestic dwelling.

The present invention seeks to provide a more easily mounted natural-light enhancement assembly than those referred to above.

According to the present invention, a natural-light enhancement assembly comprises a sheet of transparent or translucent material profiled so as in cross-section to present a series of projections, light-receiving surfaces of which are all inclined in the same sense to the mid-plane of the sheet at an angle of be tween about 30 and 60 , a value of about 45 , e.g. 45" +5 , currently being preferred.

Conveniently, the projections are each in the form of an approximately 90" prism. In one such case, the wall of the prism are convex.

Conveniently, the assembly is mounted with the mid-plane of the assembly substantially vertical or within 20 of the vertical.

Alternatively, the assembly is mounted with the mid-plane of the assembly at an angle in excess of 20 to the vertical.

Conveniently, the mean thickness of the sheet is about 3 mm to 5 mm and the sheet is grooved to a depth of about 1 mm to about 3 mm to provide said prismatic projections.

Conveniently, the sheet is one of a plurality of such sheets, one or more of which are inclined so as to redirect incident light forwardly i.e. in the same general direction as the incident light, by refraction within the sheet and one or more others of which are inclined so as to redirect light rearwardly i.e.

in the opposite general directions to the incident light, by internal reflection within the sheet.

Conveniently, the sheets are arranged one above the other with alternate ones of the sheets redirecting incident light forwardly by refraction and the intervenening sheets redirecting incident light rearwardly by internal reflection.

Conveniently, the total light-receiving area presented by the light-refracting sheets bears a 3:2 ratio to the total light-receiving area presented by those sheets relying on internal reflection to redirect the incident light.

If desired, the sheets may be of approximately the same size as one another but in this case the number of light-refracting sheets present in the assembly will preferably bear a 3:2 ratio to the number of sheets relying on internal reflection to redirect the incident light.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawing in which: Figures 1 and 2 are diagrammatic end views of part of a first embodiment of the invention mounted to give forward and rearward lightredirection respectively; Figure 3 is a scrap diagrammatic end view of a second embodiment of the invention designed to give both forward and rearward light-redirection; and Figure 4 is a diagrammatic end view illustrating a modified form of the first embodiment mounted to give forward light-redirection.

Thus referring first to Fig. 1 of the drawings, this shows part of a natural light enhancement assembly comprising a sheet 10 of transparent plastics material profiled so as in cross-section to present a series of projections 12 each in the form of an approximately 90" elongate prism.

Conveniently, the sheet is extruded acrylic e.g. ''perspex" or polycarbonate.

The broken line 14 in the Figure, indicates the path of light incident on sheet 10 and refracted downwards as illustrated. The amount of light transmitted by sheet 10 in this mode of operation can be increased by tilting the sheet at up to 20 to the vertical but as soon as the critical angle at the rear face 16 is reached, total internal reflection will occur. This is illustrated in Fig. 2 for a 25 tilt situation.

Obviously, there is clearly scope for adjustment of the tilt value between the two extremes indicated to accommodate variations in sun position over the month but even so the basic choice is whether to forwardly redirect the light as shown in Fig. 1 or to rearwardly redirect it as shown in Fig. 2. This, too, will obviously decide whether it is best to hang the assembly near the north wall or the south wall of the greenhouse if, as will usually be the case, the ridge of the greenhouse lies along the east-west direction.

Fig. 4 illustrates a modified form of the first embodiment in which the projections 12 are slightly convex so as to spread the transmitted light and give a somewhat more uniform light distribution across the floor of the greenhouse. In the example shown, the peak angle of the projections is about 90" and that of the troughs about 70" but other values are possible e.g. with the peak angle greater or less than 90".

Fig. 3 shows an alternative design of natural light enhancement assembly in which the incident light is redirected to either side of the assembly by having some sections (sections 1) arranged in the manner of Fig. 1 and some sections (sections 2) arranged in the manner of Fig. 2. Obviously, in the latter case, the best place to suspend the assembly is from the central ridge of the greenhouse.

As before, adjustment is possible to suit the prevailing light conditions, this time by rotational adjustment of the sheets in each group of sheets.

Calculations show that the light losses from sections 1 and 2 differ because of the different redirection mechanism involved. The ratio of transmitted light to reflected light, everything else being equal, is about 2:3 and to compensate for this the ratio of the height dimension of sections 1 to their separation is in the ratio 3:2. The corresponding dimension of the inclined sections 2 is ideally the maximum allowable for non-interception of light directed towards the vertical sections 1 above each said inclined section.

Claims

1. A natural-light enhancement assembly comprising a sheet of transparent or translucent material profiled so as in cross-section to present a series of projections, light-receiving surfaces of which are all inclined in the same sense to the mid-plane of the sheet at an angle of between 30 and 60".

2. An assembly as claimed in Claim 1 in which the surfaces are inclined at about 45" to said mid-plane.

3. An assembly as claimed in Claim 1 or Claim 2 in which the projections are each in the form of an approximately 90" prism.

4. An assembly as claimed in Claim 3 in which the walls of the prism are convex.

5. An assembly as claimed in any preceding claim in which the assembly is mounted with the mid-plane of the assembly substantially vertical or within 20 of the vertical.

6. An assembly as claimed in any of Claims 1 to 4 in which the assembly is mounted with the mid-plane of the assembly at an angle in excess of 20 to the vertical.

7. An assembly as claimed in any preceding claim in which the mean thickness of the sheet is about 3 mm to about 5 mm and the sheet is grooved to a depth of about 1 mm to about 3 mm to provide said projections.

8. An assembly as claimed in any preceding claim in which the sheet is one of a plurality of such sheets, one or more of which are inclined so as to redirect incident light forwardly as hereinbefore defined by refraction within the sheet and one or more others of which are inclined so as to reflect light rearwardly as hereinbefore defined by internal reflection within the sheet.

9. An assembly as claimed in Claim 8 in which the sheet are arranged one above the other with alternate ones of the sheets redirecting incident light forwardly by refraction and intervening sheets reflecting incident light rearwardly by internal reflection.

10. An assembly as claimed in Claim 9 in which the total light-receiving area presented by the light-refracting sheets bears a 3:2 ratio to the total light-receiving area presented by those sheets relying on internal reflection to redirect the incident light.

11. An assembly as claimed in Claim 10 in which the sheets are of approximately the same size as one another but the number of light-refracting sheets present in the assembly bears a 3:2 ratio to the number of sheets relying on internal reflection to redirect the incident light.

12. An assembly substantially as hereinbefore described with reference to, and/or as illustrated in, Figs. 1 and 2 of the accompanying drawing.

13. An assembly substantially as hereinbefore described with reference to, and/or as illustrated in, Fig. 3 of the accompanying drawing.

14. An assembly substantially as hereinbefore described with reference to, and/or as illustrated in, Fig. 4 of the accompanying drawing.