Lighting method and apparatus having a variable illuminated field

A lighting apparatus has a lighting filament (3), a first lens (1) disposed at a fixed distance from the filament (3), divergent light from the filament falling directly on the first lens (1) which reduces but does not eliminate the divergence of the light in all directions about the optical axis upon passage of light through the first lens, and a sleeve (12) carrying a second lens (2) mounted for sliding movement relative to the box. The second lens (2) receives divergent light directly from the first lens (1) and reduces the divergence of the light upon passage of the light through the second lens, the focal length of the second lens being greater than 1 1/2 times the focal length of the first lens and the distance between the lenses being less than 1 1/2 times the focal length of the first lens. The illumination pattern is high-intensity but does not have a sharp contour so that it may be used in a surgical operating room.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a lighting method and a lighting apparatus having 
a variable illuminated field, in particular for operating-rooms. 
2. Description of the Prior Art 
Surgical operations call for high-intensity lighting systems which satisfy 
certain functional criteria. The illuminated field must have uniform 
lighting but must not have a sharp contour in order to avoid lighting 
boundaries which produce disagreeable contrasts for the surgeon's eye. 
Some operating-room lighting systems project a light source on zones having 
fixed dimensions of contours and constant illumination. These zones can be 
displaced and superimposed in order to vary the level of illumination of 
the field under observation. 
U.S. Pat. No. 4.745.526, the disclosure of which is considered as 
incorporated in the present disclosure, is directed to such known lighting 
systems. 
One object of the invention is to propose a lighting system for producing 
at a predetermined distance from an operating-room lighting lamp an 
illuminated field which is variable both in dimensions and in 
illumination. 
SUMMARY OF THE INVENTION 
The invention is directed to a lighting apparatus, particularly for 
operating rooms, comprising a box, said box supporting a lighting filament 
and a first convergent lens, said convergent lens being disposed at a 
fixed distance of said filament, wherein a sleeve carrying a second 
convergent lens slides relatively to said box along an optical axis common 
to said filament and two said convergent lens, and wherein the focal 
distance of said second lens is superior to one and half times the focal 
distance of the first lens. 
According to one embodiment of the invention, means for displacing said 
sleeve cooperate with two abutments, said abutments being apart from a 
distance inferior to one and half times the focal distance of the first 
lens. Said means for displacing comprises advantageously a fixing screw 
cooperating with a lateral groove of the box. Said screw comprises 
preferably a shoulder pressing on a flat surface around said groove when 
said second lens is in position. 
The invention is also directed to a lighting method for obtaining from a 
lamp filament an illuminated field which is variable in diameter and in 
illumination, comprising following steps: 
placing a first convergent lens having a fixed focal length F.sub.2, in 
fixed relationship with the lamp filament, 
displacing a second convergent lens having a focal length F.sub.2, this 
lens being placed on the other side of the first lens with respect to the 
filament according to a variable distance D from the first lens on the 
axis of the system, 
under the following conditions : 
the focal lengths satisfy the double inequality 1.5 F.sub.1 &lt;F.sub.2 &lt;4 
F.sub.1 
and the distance D between the two lenses corresponds to the double 
inequality O&lt;D&lt;1.5 F.sub.1.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, it is seen that the lighting system in accordance with 
the invention is composed of an operating-room lighting lamp, the filament 
of which is represented schematically at 3, of a first convergent lens 1 
which is fixed and placed near the filament 3, and of a second convergent 
lens 2 which is movable along the axis of the system. By "convergent" is 
meant that the divergence of light falling on the lens is reduced by 
passage through the lens. 
The diameter of the first lens 1 determines the aperture of the system. The 
second lens 2 serves to project the illuminated field in combination with 
the first lens 1. At a predetermined distance from the filament 3 of the 
operating-room lighting lamp, the illuminated field is represented by its 
diameter in FIGS. 1 and 2. In FIG. 1, since the two lenses 1 and 2 are 
very close to each other, the illuminated field has a large diameter 4. 
Referring to FIG. 2, since the two lenses 1 and 2 are spaced apart, the 
illuminated field has a smaller diameter 5. By varying the spacing of the 
two lenses, one varies the diameter of the illuminated field but the 
illumination of the field remains uniform. 
However, when the diameter of the field varies, its illumination varies as 
the inverse of the square of the diameter, 
In order to ensure uniformity of illumination of the field, one employs the 
combination of the geometrical aberrations of the two lenses 1 and 2 in 
order to spread-out the projection spot of the filament 3 to a sufficient 
extent. 
In a particular example of construction, the lenses 1 and 2 have the 
respective focal lengths : 
F.sub.1 =67 mm and F.sub.2 =174 min. 
The diameter of the illuminated field at a distance of 1 m varies from 220 
mm (4, FIG. 1) to 130 mm (5, FIG. 2) in respect of a displacement of the 
second lens of 48 mm. 
According to the invention, in order to obtain this uniform and variable 
illumination as well as the variation of illumination as a function of the 
variation of the illuminated field, with only two convergent lenses, the 
focal lengths F.sub.1 and F.sub.2 of the two lenses 1 and 2 respectively 
satisfy the double inequality : 
1.5 F.sub.1 &lt;F.sub.2 &lt;4 F.sub.1. 
And the distance D between the two lenses corresponds to the double 
inequality : 
O&lt;D&lt;1.5 F.sub.1. 
Referring now to FIG. 3, an apparatus according to the invention supports 
in axial relationship along a common optical axis a first convergent lens 
1, a second convergent lens 2 and a lighting filament 3. 
To this effect, the apparatus comprises a box referred to in its whole by 
reference 6. The box 6 is constituted by a hood 7 and a cylinder 8 in 
fixed relationship. 
The hood 7 receives in its inner space a filament 3. Cylinder 8 supports at 
one extremity a first lens 1 which is in position by a threaded ring 9. 
Cylinder 8 comprises also a lateral groove 10, in which a screw 11 with a 
knurled head is slidably mounted. 
Groove 10 is limited by two extremities 1Oa-10b constituting sliding 
abutments for screw 11. 
The screw 11 with a knurled head cooperates with a sleeve 12 supporting a 
second lens 12 and is advantageously provided with a shoulder 13, which 
presses against a flat surface 14 around the groove 10, in order to hold 
sleeve 12 and lens 2 in a desired position. 
While the invention has been described with reference to a particular 
embodiment, the invention is in no way limited to this embodiment but 
covers on the contrary various modifications of the details and 
embodiments within the scope and spirit of the invention.