JPH0130255B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The reflecting mirror of a projection lamp is often an ellipsoidal one. In the case of such an ellipsoidal surface, light emitted from the first focal point of the ellipse is condensed at the second focal point.

However, in reality, the light source is not a point but a filament having a volume, so the amount of light passing through the aperture window varies depending on its shape. Since a filament is generally a cylindrical coil having the same diameter over its entire length, the following disadvantages arise.

In FIG. 1, a filament 2 of a cylindrical coil is vertically attached to the first focal point _O1 of a mirror 1 having an ellipsoidal surface. Further, the second focal point O ₂ of the ellipse forming the mirror 1 is located slightly forward of the center of the window of the aperture 3.

In this case, the light rays reflected from points a and b at the ends of the filament 2 and hitting arbitrary reflection points P ₁ , P ₂ , P _{3 ,} etc. on the surface of the mirror 1 are diffused and reach the aperture 3.
The amount of light passing through the windows is reduced, reducing efficiency.

The same applies when the filament 2 is placed horizontally as shown in FIG.

In order to solve such problems,
As with the idea described in Japanese Patent No. 14288, a flat coiled filament is provided at the first focal point of the spheroidal surface in an attempt to bring it one step closer to a point light source. However, as long as the filament has a volume, it goes without saying that it cannot become a perfect point light source.

The purpose of this invention is to solve the above-mentioned problems. Instead of making the shape of the filament closer to a point light source, the invention aims to create a three-dimensional shape guided by the aperture size of the projector determined by the purpose of use and the shape of the mirror condenser. To provide a filament in which light rays exiting the filament are efficiently focused within a window of an aperture by enclosing the filament in a shape.

First, in Fig. 3, mirror 1 and the first focal point
The positional relationships among O ₁ , second focal point O ₂ , aperture 3, etc. are the same as in the conventional example shown in FIGS. 1 and 2, and mirror 1
In order for the rays reflected by hitting arbitrary reflection points P ₁ , P ₂ , P ₃ , etc. on the surface of , to pass through the window of the aperture 3, there are points A ₂ , B ₂ before and after the first focal point O ₁ . For example, A ₂ as shown by the diagonal lines passing through point P ₂ on the mirror surface to the upper and lower ends C and D of the window of aperture 3.
The light must be directed from between B ₂ and towards P ₂ .
This point P ₂ is moved and drawn as points P ₁ , P ³ , Pn on the surface of mirror 1, and P ₁ , A ₁ , P ₁ , B ₁ , P ₃ ,
When the virtual envelope F of A ₃ , P ₃ , B ₃ , Pn, An, Pn, Bn, etc. is determined, it becomes approximately triangular when viewed from the side as shown in FIG. Further, since the mirror 1 is a rotating body centered on the straight line L connecting the first focal point O ₁ and the second focal point O ₂ of the ellipse, the envelope F has a substantially conical shape.

For the above reason, all light rays emitted from points inside the envelope R will pass through the window of the aperture 3, so it is preferable to make the shape of the filament approximately conform to the inside of the envelope F.

That is, the filament may be arranged in a conical shape within the range of the envelope F as in the case of the coiled filament 5 shown in FIG. 6 should be approximated.

In this case, the cross section perpendicular to the axis of the filament 6 has a shape that corresponds to the envelope F, but the cross section in the axial direction has a rectangular shape in the case of FIG. Therefore, it is advisable to narrow down the spiral shape at both ends of the filament 6 so as to make it as close to the envelope as possible.

As described above, this invention assumes by drawing a virtual envelope F such that all the light emitted from the filament at the first focal point _O1 in the ellipsoidal reflecting mirror 1 enters the window of the aperture 3. Since the filament 5 or 6 formed into a conical or triangular shape that fits approximately within the envelope F of the lever is used, almost all of the light rays emitted from the filament pass through the window of the aperture 3. The efficiency of the lamp is therefore significantly increased. In particular, 100V,
By using the filament of the present invention, even in a lamp with a long filament length such as a 120V high voltage projection lamp, a much brighter screen can be obtained compared to a lamp using a conventional filament of the same power.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views explaining the operation of a lamp using a conventional filament, and Figures 3 and 4 are
The figure is a side view illustrating the operation of a lamp using the filament of the present invention, and FIGS. 5 and 6 are perspective views showing examples of the filament of the present invention. 1... Reflection mirror, 3... Aperture, 5, 6... Filament, O ₁ ... First focal point, O ₂ ... Second focal point, F
…envelope.

Claims (1)

[Claims] 1. In a projection lamp in which a filament is provided at the first focal point of an ellipsoidal reflecting mirror to condense light at the second focal point, the shape of the filament is changed to the second focal point.
A virtual light point on the outline of the aperture window placed near the focal point reaches any reflection point on the mirror on the same plane that includes that point and the optical axis of the mirror, and is reflected to the first
A filament of a projection lamp whose profile approximately conforms to the envelope near the first focus, drawn by an imaginary ray directed near the focus. 2. A filament for a projection lamp according to claim 1, wherein the filament has a conical shape. 3. The filament for a projection lamp according to claim 1, wherein the filament has a triangular cross section.