FR2465313A1 - ELLIPSOIDAL ENCLOSURE FOR INCANDESCENT LAMPS, INCLUDING MEANS FOR RETURNING INFRARED ENERGY - Google Patents

Abstract

THE INVENTION RELATES TO AN ELECTRIC INCANDESCENT LAMP INCLUDING A COATING 12 INTENDED TO REFLECT INFRARED ENERGY TOWARDS THE FILAMENT 22 TO RAISE ITS OPERATING TEMPERATURE, THE ENCLOSURE 42 BEING ELLIPSOIDAL SHAPED AND THE FILAMENT AND THE ENVELOPE AND ONE IN RELATION TO THE OTHER SO AS TO REDUCE LOSSES DUE TO ABERRATION AND TO PRODUCE A MORE UNIFORM TEMPERATURE DISTRIBUTION ALONG THE FILAMENT.

Description

We know the use of a transmitting coating

  visible rays and reflecting infrared rays

  ges, applied to the envelope of an incandescent lamp

  so as to reflect the infrared energy towards the fila-

  and increase its operating temperature, and thereby reduce the amount of energy consumed by the filament at a desired temperature. A typical approach to this problem is to use spherical optical precision envelopes and a compact filament disposed in the optical center of the envelope. A lamp of this type is described in US patent 4,160,929 granted

July 10, 1979 to the author of this request.

  From a practical point of view, it is not possible to make a point source or a spherical filament. In

  general, it has been found that an elongated filament, is bispi-

  led, either three-spiral, mounted either horizontally or

  vertically with respect to a spherical envelope, cons-

titue the most practical embodiment of a lamp intended to be provided with a coating reflecting the

infrared rays. However, when using a reflective

  optical precision spherical tor in conjunction with a non-spherical filament such as an elongated filament, part of the radiation reflected by the reflector on

  the envelope is lost due to aberrations at extremi

filament tees. When this radiation is lost during a reflection, it is practically lost for

  all of the following reflections on the reflective coating

shrinking of the envelope, unless you use a type

any recovery mechanism.

The present invention relates to an incandescent lamp

  cence improved in which the envelope is ellipsoldale and provided with a coating to reflect infrared energy. The filament is in the form of an elongated cylinder centered inside the reflecting envelope. The ellipsoXdale envelope is constructed so that its two foci are located on the axis of the filament and at predetermined distances from each

  end of the filament to reduce losses by aberra-

  tion. Using this approach to the problem can reduce aberration losses by about half

  with respect to a sphere containing the same cylindrical filament

drique. Likewise, the use of an ellipsoldal element concentrates the IR radiation returned at two points located at predetermined distances from the ends of the filament, rather than at a single point. This makes the gradient of

more uniform temperature.

  The invention will now be explained in more detail with reference to the accompanying drawings in which: FIG. 1 is a view in elevation and in section of an incandescent lamp of the prior art, FIG. 2 is a side view of the lamp of Figure 1, showing the effects of aberrations, Figure 3 is an elevational view of an ellipsoldic envelope showing the principles of the invention, and Figure 4 is a sectional view of the lamp of the

  Figure 3, showing the location where the filament is fixed.

  FIG. 1 represents a type of incandescent lamp j0 of the prior art. The lamp comprises an envelope 11, which is preferably of a desired optical shape, the illustrated shape being spherical with the exception of the part of

  based. The lamp includes a device for returning the energy

  infrared (IR) light produced by the filament when this filament is heated to incandescent. The lamp 10 is coated on the main part of its spherical surface, i.e.

inside or outside, with a strong 12 coating-

  transparent for visible wavelength energy and highly reflective for infrared wavelength energy. A suitable coating is described in

  US Patent 4,160,929 mentioned above. We can also

their use other coatings.

A filament 22 is mounted on a pair of bushing wires 18, 20, held in a rod or tree 17. The bushing wires 18, 20 come out of the tree by being connected

  to electrical contacts 14, 16 provided on a base 13.

The shaft 17 also includes a tubular passage (not shown

  by which you can create a vacuum inside the lamp envelope, and fill it, if desired, with a gas. Gases suitable for this use consist, for example, of argon, a mixture of argon and nitrogen, or

  a higher molecular weight gas such as krypton.

  The lamp can also function as a lamp of the type

empty.

When the voltage is applied to the lamp, the filament 22 becomes incandescent and produces energy both in the visible range and in the infrared range. The exact spectral distribution of the filament depends on the

  resistance of this filament. Operating temperatures

  typical filaments are included in the range

ranging from approximately 26501K to 29001K, although the

  Also at temperatures of 20001K or 30500K is also possible.

  filament function increases, the spec-

  trale shifts towards the red, and therefore produces more energy

infrared.

  The coating 12, in combination with the optical form of the lamp, serves to return to the filament a substantial part, preferably as large as possible,

i.e. about 85% or more, of the IR energy produced

  te by the filament. When the energy is reflected towards the filament, it increases the operating temperature and thereby decreases the power (consumption in watts)

  necessary for the operation of the filament at this temperature

ture. Figure 2 shows how the aberration effects are produced from the ends of the filament. This

  figure is a section of the lamp along the longitu-

  dinal of the envelope. In view of the explanation, we consider

  will see that the envelope is a closed sphere in this direction. It will be assumed that the filament 22 has a length and that the center C of this filament is located at the optical center of the spherical envelope. The filament is also in the general form of a cylinder of diameter D. Considering the rays having their origin at one end O of the filament at a point located off the axis, when the filament is brought to incandescent, these rays are products - actually on a series of angles that cover a spherical surface. Two rays R1 and R2 of this type are shown directed at an almost acute angle

  relative to the axis of the filament. Two other spokes

felt, S1 and S2, are produced by forming a rather obtuse angle with respect to the longitudinal axis of the filament. As shown in the figure, the image point of rays R and R2 is located near the image point I2f which is outside the filament, while the image points of rays S1 and S2 are close to the image point Il which is at the end of the filament. We can demonstrate that for all the rays starting from the terminal point O, the image points of a large

number of these rays is located in a region outside

laughing from the end of the filament opposite to the end O. The infrared energy which is not reflected on the filament

is lost, unless it is recaptured.

  A similar analysis can be performed for the radii emitted from the end of the filament which is opposite to O. An analysis will be presented below to calculate

these terminal losses.

  The total aberration losses come from a distortion of the image associated with the sides, or the external surface of the filament, as well as at its ends. The losses on the sides arise from the fact that the geometry of the filament does not precisely conform to the shape of

the envelope, so that the wave front pro-

  coming from the sides of the filament also does not correspond exactly to the envelope and that there is a certain degree

aberration when they are returned to the filament.

  We can see that the aberration losses L prove-

  from the sides of an elongated filament centered on the optical center of an optical precision sphere of radius R are the following: TR Ec Ac.Ac.Ae) o: e represents the length of the filament, R represents the radius of the cylinder of the filament, Ac represents the surface area of the cylinder which is a function of the diameter of the filament, AE represents the terminal surface of the filament, Ec represents the radiation power of the cylinder, E represents the radiation power of the end

filament.

  For a filament of 13.0 mm in length contained in an envelope of spherical glass G-25 of 80 mm, when E c = 0.55 and when Ee is approximately 1, the lateral losses Lc which are calculated are about 3.1%. This means that this amount of infrared energy will only be

  not returned to the filament and will be lost.

  Figure 3 shows an ellipsoidal envelope formed to reduce terminal losses, while Figure 4 is a schematic elevational view of the shape of the ellipsoldic envelope and the location of the center

  filament. In Figure 4 and to facilitate explanation

tion, the envelope is assumed to be completely ellipsoidal.

  The same reference numbers already used in Figure 1 are used in Figure 3. As can be

  see, envelope 42 is ellipsoldic in shape, that is,

  say that it is constituted by an ellipse rotated on 3600 to produce an ellipsoid. The envelope comprises a base 13 with a rod and a tubular passage. The incandescent filament 22, which is preferably two-spiral or three-spiral, is treated as a cylinder whose axis is

arranged along the main axis of the ellipse. The envelope

  pe 42 is coated inside or outside with a coating 12 which reflects the infrared and leaves

pass visible rays.

  If we refer to Figure 4, the envelope 42 is

  formed in relation to the filament so that the use

  cement of the focal points of the ellipse are arranged so as to minimize the sum of the aberrations of extremities and lateral aberrations. In an ellipsoid, rays emitted near one of the foci located along the

length of the filament are returned by the coating available

  placed on the wall of the envelope towards associated points located near the foci on the opposite side, considering the center C as the dividing line, of the filament from which the rays are emitted. Usually it takes only one internal reflection. However, the visible energy passes through the coating in an amount determined by the transmittance of the coating, when it strikes to

the first time this coating.

  The rays emitted in places close to the hearths have no aberration. However, there is always a

aberration at the ends of the filament, due to distortion.

In an envelope reflecting infrared rays-

ges, whether spherical or ellipsoldal, the image of a ray emitted at one end of the filament and at an angle e with respect to the axis of the filament, is formed at a certain distance S at the rear of l opposite end given by equation: 2 (J / 2cosLO C2) The distance between the end of the filament and the center is J / 2. Thus, for a certain range of angles of the rays emitted at each end of the filament, there is a loss, the rays not forming the image on the opposite end of the

filament after reflection on the coating. We can demon-

  trer that the rays located inside the angle formed between 1 and 82 are lost for the filament. In other words, the rays coming from the left end of the

filament between the two conical angles are not inter-

caught by the filament.

The LE end loss can be calculated as follows: LE =. (10 $ 66 -.cos O2) f EeAe k J

  o the other quantities have been defined above.

  For a 13 mm long filament contained in a

80 mm diameter G-25 envelope, O1 and e2 are

  approximately 10.80 and 64.30. The end aberration loss LE is about 6.8% and the aberration loss on the sides is about 3.1%, as already mentioned, which gives a total of 9.9%. This would constitute the loss in a spherical enclosure where the elongated filament is centered

practically precisely.

  When we want to determine the dimensions of the ellipse

  in order to minimize the aberration losses, we consider

dère that for an ellipse which is not too eccentric, the aberration of end depends on the distance separating it from one of the focal points, in the same way as the aberration depends on the distance separating the end of the filament of center of the sphere. This spherical aberration depends on the square of

  the distance from the center, and we assume that the aberr-

  tion depends on the square of the distance from the nearest of the two foci located at a distance - X from the center of the ellipse. The loss by elliptical aberration L is then considered as the sum of the end losses and the lateral losses: (2 X) xz2 2 L- te) _L ___ (4_

o L0 = loss along the cylinder.

The terms - X) and X in the parentheses come from -

  lateral aberration at a certain distance from the

center of the ellipse and toward the center of the ellipse.

When X = 0, the ellipse becomes a sphere and L = LE + Lco as desired. 4L

The minimum aberration is given by determining- = 0.

  When we solve this equation, we end up with: dK X _ _ (Lr + L), ()

due Iz + 2Lc.

If LE = 0, X is halfway between the end of the filament and the center. The foci are therefore located in X which is at a distance of a quarter of the length of the filament from the end of this filament. In this location of the hearths, the elliptical aberration is a quarter of the aberr-

  ration of a filament contained in a spherical envelope.

If Lc = 0 X is then at the end of the filament and there is no elliptical aberration. Thus, the spherical aberration is reduced by a factor of a quarter or less to

inside the ellipse.

  In a practical example, X = 0.76 (</ 2) and the foci are located approximately three-quarters of the distance between the center and an end. The total aberration is then around 2.4%, compared with the 9.9% around that

we observe with a sphere.

As mentioned, the use of an ellipsoid having two foci has the additional advantages that the reflected IR radiation is concentrated at two points, which are the foci, rather than at a single point when it comes to spherical geometry. This allows the temperature to be distributed more evenly over the

  along the length of the filament. In addition, the energy

the view is concentrated in two points rather than in one and there is less defocus between them. Because the

light output of a filament is a function of the temperature

  crosses out, and decreases at the colder positions, the lower the

  distribution of the temperature is regular and more the emission

  lumens is important. Likewise, uneven temperature gradients result in reduced filament life and a temperature gradient

  more regular avoids this drawback.

Claims (7)

1. An incandescent electric lamp comprising: an ellipsoidal envelope provided with a base part or base, an incandescent filament mounted inside the envelope, means for supplying electrical energy to the filament and the heat incandescently so as to obtain energy both in the infrared range and in the visible range, means of cooperation with the envelope to strengthen see through the envelope and towards the filament a subset   of the infrared energy produced, and for trans-   put a substantial part of the energy towards the envelope   gie produced by the filament in the visible range, characterized in that the filament (22) is elongated and mounted along the main axis of the envelope ellipsoid (42) the focal points of the ellipsoid being arranged on the filament at points to reduce losses by aberra- lateral and end filament tion.   2. Electric incandescent lamp as claimed cation 1, characterized in that each of the foci is   located at a certain distance between a respective end of the filament and about half the distance to than in the center of the filament.   3. Incandescent electric lamp according to the claim   tion 2, characterized in that each of the fireplaces is   dried at a respective end of the filament to make minimal lateral losses.   4. Incandescent electric lamp as claimed   cation 2, characterized in that each of the hearths is arranged at approximately half the distance between   a respective end of the filament and the center of the fila- is lying.   5. Electric incandescent lamp as claimed   cation 2, characterized in that each of the foci is located approximately three quarters of the distance between the center of the filament of each respective end. 6. Electric incandescent lamp according to claim 1, characterized in that the cooperation means consist of a coating applied to the wall of the envelope 7. Incandescent electric lamp as claimed   cation 1, characterized in that each of the foci is located at a distance such that a distribution is obtained   more uniform temperature along the filament.