Optical components for daylighting and other purposes

Details Optical components for daylighting and other purposes Optical components for daylighting and other purposes

2001-06-12

2002-08-20

Sikder, Mohammad (Department: 2872)

Optical: systems and elements

Glare or unwanted light reduction

With mirror

C359S609000, C359S613000, C359S599000

Reexamination Certificate

active

06435683

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical components for daylighting and other purposes.
2. Description of Related Art
The term “daylighting” as used in the specification will be understood to refer to applications in which natural daylight is allowed into buildings or other structures (such as vessels or aircraft) through openings provided with means by which the amount of usable light entering through the opening is enhanced by various means. This may be achieved, for example, by diverting light from incident angles at which they would not otherwise provide useful light within the building or other structure, or by capturing light passing the opening which would not otherwise enter the building through it.
A number of previous attempts have been made to improve the daylighting of buildings through transparent elements fitted in openings, such as doors and windows. It was appreciated at an early stage that the provision of a plurality of elementary prism-like structures on one side, or even on both sides, of a pane of glass would provide diversion of incident light utilising the known properties of a prism to refract the light. The benefit of such light-diverting properties lies in the fact that light incident on a window or glazed door from the outside is of greater intensity at high angles of incidence (assuming that the glazing element is planar, lies in a substantially vertical plane, and angles of incidence are measured from the normal or horizontal plane) which means that with traditional plane glazing elements the strongest light arriving from the highest angles passes straight through to illuminate a limited region on the floor of the interior of the building closest to the window, whereas regions further into the room, although they receive light arriving at shallower angles of incidence, are not so strongly illuminated. It is a well-recognised phenomenon that in large rooms lit by a single window in one wall, the level of daylight illumination nearer the back wall and further from the window is less, and frequently considerably less, than the illumination closer to the window.
So-called “daylighting” glazing elements have sought to rectify this situation by diverting light arriving at high angles of incidence, by refraction as it passes through the glazing element, so that the exit angle of at least some of the light arriving from an incident angle above the horizontal is itself above the horizontal so that this light is directed upwards and towards the back of the room instead of being directed downwards to the floor.
Previous attempts to provide daylighting glazing, however, have suffered from the fact that the light-diverting optical properties of the glazing elements have resulted in diffusion of the light into a range of different directions so that an observer within a room has no view through it because light arriving at his eye comes from a wide range of different directions. For this reason, although the daylighting principle is desirable the prior art systems have effectively closed the room from the outside which is a considerable disadvantage from the point of view of the occupants, reducing the daylight to little more than the equivalent of artificial light even though it may have the desirable properties of day light in term of spectral range and colour temperature.
In recognition of this problem a number of element profiles have been developed which are capable, when used in the vertical orientation of traditional glazing, that is with panels lying in a substantially vertical plane, of diverting light incident at high angles above the horizontal and allowing light incident at shallow angles close to the horizontal (both above and below it) to pass through substantially undeviated whereby the occupants of a room can obtain a view through the glazing elements to the outside whilst the high intensity light arriving from high in the sky is diverted towards the back of the room to improve the level of illumination.
The applicant's own earlier International Applications Nos. PCT/GB94/00949 and PCT/GB97/00517 describe various different profiles using both individual elements and components comprising composite structures, for achieving this desirable effect. One of the profiles utilised comprises what amounts to a parallel series of shaped grooves in one face of an element which, in use, is orientated with the grooves horizontal. The size of the grooves is such that they do not exceed the average pupil diameter of the human eye, but are not so small that diffraction effects predominate, so that the eye effectively integrates the optical effects making it possible to see through the element without significant distortion or interruption of the image.
Of course other applications of the optical component of the present invention are not excluded, and its description with reference to daylighting purposes is to be understood as being without prejudice to the generality of the invention. In particular, the optical component of the present invention may be utilised as a cover for a light source where it may be desired to divert light generated thereby or for any of a range of other applications in which optical components may be used, such as in the illumination of screens (both those bearing images and those acting as barriers) transmission of images and/or illumination of advertising signs, shop windows or the like. When diverting light by the use of refraction and/or reflection one problem which continually arises is that of chromatic dispersion which can be of significance especially if the diverted light is to be used for imaging purposes. Another problem arising with daylighting elements generally, is the possibility of glare arising from, for example, the region immediately around the sun, which is usually out of the normal line of vision but which, because of the diversion of incident light, may have an apparent direction which impinged detrimentally on the field of view of occupants within the building. Brightness variations from day-to-day can also mean that a daylighting system which works well for average conditions is inadequate in dull or overcast conditions and excessively or uncomfortably bright in clear-sky conditions.
SUMMARY OF THE INVENTION
The present invention seeks to provide means by which these disadvantages of daylighting systems can be mitigated at least to some extent, and to provide configurations of daylighting elements and components which will improve the performance of daylighting systems generally and extend the range of applications to which they can be put. The present invention also seeks to introduce further ideas and concepts about how optical elements can be adapted to enhance the internal illumination of buildings.
According to one aspect of the present invention, therefore, an optical element of the type comprising two optically transparent bodies each having two major faces one of which is interrupted by a plurality of cavities separating the said major face into a plurality of first elementary surfaces, between the cavities there being cavity separators defined by second elementary surfaces at which light incident through the corresponding optically transparent body above a certain threshold angle is reflected by total internal reflection and below which threshold it is transmitted and refracted, in which the shape of the cavities of the two bodies is complementary and such that the cavity separators between the cavities of one optically transparent body and the cavities of the other optically transparent body interpenetrate one another such as to define, for each cavity, at least two voids between facing elementary surfaces at which total internal reflection takes place.
In embodiments of the present invention the interpenetrated bodies may be in the form of substantially flat panels positioned face-to-face and these bodies may be sufficiently rigid to be self-supporting, or may be formed as thin films to be carried on other transparent supports such

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