| 摘要 |
The modified Fresnel lens includes a zone giving improved utilization of light internally reflected in an associated guide layer The guide comprises several progressively elongated glass layers, stacked under spring compression in a reference frame. A filament or arc light source in an elliptical reflector illuminates the guide's entry face (the coplanar ends of the stacked layers), normally. Light penetrating each layer, axially, is internally reflected at its terminating facet . Optionally., a layer may terminate in a stepped facet. Reflected beams exit through the side faces. Each beam is collimated by a Fresnel lens and directed on the illuminated area as the component of a composite beam oriented (E) generally parallel to the vehicle's longitudinal axis, to which the guide is mounted transversely. Where a cut-off beam is required one or more component beams is obstructed by a mask fixed between guide and lens, or on the latter's exit face. Each layer's emitted beam includes a primary fraction, ie. light (14) traversing the layer (12) with reflection only at the terminating facet, and a secondary fraction (eg. 16) internally reflected between the main surfaces. Primary light is confined to the lens's (20) central zone, secondary to the outer. The latter, though less intense, is quantitatively significant. The invention seeks as far as possible to make it available in the target illuminated area. Using molding techniques, a horizontal boundary is set somewhat above the center, the lens below following conventional Fresnel design for the primary light. The upper zone, for the secondary light is also Fresnel configures, but on a different center, with different optical characteristics. Optionally, the upper zone forms a set of prisms, curved or flat-sided, with vertical or horizontal striation. Opt., also, the effect is obtained by two separate lenses instead of a composite.
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