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(11) | EP 0 233 016 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Fluorescent tube lampholder |
| (57) A fluorescent tube lampholder comprises a flat base (30) which is arranged to receive
the end of a fluorescent tube, and two sockets (32, 34) to receive the pins of the
tube. The distance (d) between the live socket (32) and the periphery of the base
(30) is greater than the distance (s) between the two sockets. Thus, the user cannot
accidentally receive a shock by inserting one of the pins into the mains socket (32)
while the other pin is free; this is prevented by the other pin fouling the base (30).
The other socket (34) need not be similarly protected since it is connected to the
starter switch side of the circuit and is therefore dead unless the tube is correctly
plugged into both the sockets. |
[0002] Fluorescent tubes are conventionally provided, at each end, with two round protruding pins spaced apart by about l3mm. When the tube is in position for use, the two pins at each end are received within corresponding sockets of a fluorescent tube lampholder. The lampholder acts both to support the tube and to provide the electrical connections to the pins.
[0003] Lampholders sold in the United Kingdom must comply with a number of specifications, such as the BS and VDE specifications, to ensure that they are safe. One requirement of the specifications is that it must be impossible for one of the two pins to be inserted into a socket in such a way that the other pin is exposed and live. Prior art lampholders have met this requirement by being one of three types, as will be described below.
[0004] Another desirable feature of a lampholder is that it can be used with, and will look attractive with, tubes of any of the three standard sizes: 26, 32 and 38mm in diameter. It is not difficult to make a holder that can be used with any one of the three sizes since the pin-spacing is always the same, about l3mm. However it is more difficult to fulfil the second critereon since holders which are large enough to be used with 38mm tubes often look unsightly when used with 32 or 26mm tubes, the main reason for the unsightly look being those parts of the holder which extend beyond the outer circumferences of the tube appearing to stick out. Finally, since tube holders are mass-production items sold in large quantities it is desirable for the holder to use as little material and as few mouldings as possible.
[0005] The first current type of holder has a large flat base, against which the end of the tube is placed, and in the centre of which are formed the two sockets. To ensure that neither pin can be inserted into one of the sockets leaving the other pin free, the base extends around the sockets for a distance greater than the l3mm pin spacing. Thus, it is not possible to insert only one of the pins since the other will always be fouled by the large base. Although this type of holder may be manufactured with few mouldings and looks reasonably attractive when used with any of the three sizes of tube (the base, however, sticking out considerably when used with the smaller sizes), the amount of material used is large.
[0006] The second current type of holder again has a flat base immediately surrounding the two sockets, but in this case the base is substantially the same size and shape as the end of the tube to be used. With this smaller-sized base it would be possible for one of the pins to be inserted into one of the sockets and the other to avoid the holder entirely and be left free; this is avoided by providing an upstanding flange which surrounds, or partially surrounds, the edge of the base. When a tube is in position this flange therefore closely surrounds one end of it. The flange is sufficiently deep in relation to the length of the pins so that, with one pin overhanging the edge of the holder and the second placed over one of the sockets, the second pin is not long enough to make electrical contact. This type of holder looks good when used with the size of tube for which it was designed, but very unsightly when used with a smaller-sized tube. Furthermore, of course, a holder cannot be used at all with a tube of a larger size than that for which it was designed; stockists therefore have to carry stocks of all three sizes of holders and tubes. And finally, the presence of the separate flange makes the holders more difficult and thus more expensive to produce; valuable material is used in providing the flange.
[0007] The third current type of socket holder is constructed so that the two sockets are normally protected by a separate rotatable member mounted on the holder base. In order to make electrical contact the two pins have to be inserted into apertures in the rotatable member and the whole tube rotated by 90°. The torque required to do this is considerable, making it impossible to achieve accidently if only one of the two pins is correctly positioned. This type of socket, being smaller overall than even the smallest tube, looks attractive when used with any of the three sizes. However, it has serious disadvantages: it is difficult and expensive to manufacture, since a separate moulding is needed for the rotatable member, and it is more difficult for the customer to use than the other types.
[0008] The invention proceeds from the recognition that protection against misconnection is only needed with respect to one of the sockets, that which is connected to the mains supply or choke. The connection in the other socket is connected to the starter switch, and will therefore be live only when both pins are connected in the proper manner. It is an object of the present invention to attempt to alleviate at least some of the problems of the prior art.
[0009] According to the present invention a fluorescent tube lampholder comprises first and second sockets, with first and second electrical contacts therein, arranged to receive first and second identical pins of a fluorescent tube, the lampholder being so shaped that one pin can touch the first contact when the other pin is not in the second socket, but that one pin cannot touch the second contact when the other pin is not in the first socket; the reason for the latter preferably being because the other pin is fouled by a part of the lampholder, for example a flat base portion or a mounting portion.
[0010] The base portion may be of any suitable shape, and may have a free edge which is substantially parabolic or hyperbolic, or is generally circular in the vicinity of the second socket. Alternatively the free edge may include generally parallel edges in the vicinity of the second socket joined by a curved connecting edge in the vicinity of the first socket.
[0011] According to a second aspect a fluorescent tube lampholder comprises a substantially flat base arranged to receive the end of a fluorescent tube, and within which are first and second sockets having first and second electrical contacts therein and arranged to receive first and second identical pins of a fluorescent tube, the minimum distance between the first socket and a free edge of the base being less than the distance between the sockets, and the minimum distance between the second socket and a free edge of the base being greater than the distance between the sockets.
[0012] The invention thus provides a fluorescent tube lampholder which is inexpensive to manufacture and which looks attractive when used with any of the three commonly available sizes of tube. Since the base needs to extend a certain distance from only one of the two sockets, less material is used than in prior art holders of a similar type.
[0013] The invention may be carried into practice in various ways and one fluorescent lamp holder embodying the invention will now be described, by way of example, with reference to the drawings, in which
Figure l is a simplified diagram showing the electrical connections to a fluorescent tube; and
Figure 2 is a simplified diagrammatic view of a fluorescent tube lampholder embodying the invention.
[0014] Figure l illustrates the electrical connections to a fluorescent tube l0 having two pins l2, l4 and l2′, l4′ at each end. These pins are received within corresponding sockets of two lampholders l6, l6′. The pins l4 and l4′ are connected together via a line l8 and a starter switch 20, while the pin l2 is connected to the mains live line 22 via an inductor 24, and the pin l2′ is connected to the mains neutral line 26. Thus, it will be seen that while the sockets into which the pins l2, l2′ fit are permanently connected to the mains supply, the sockets into which the pins l4, l4′ fit are connected only to the starter switch, and are dead until both the pins l2, l4 or the pins l2′, l4′ make electrical contact. It would therefore be entirely safe if either or both pins l4, l4′ were connected with the corresponding sockets on the starter switch side of the circuit, and the pins l2, l2′ were free and unconnected. It would, however, not be safe for the pins l2, l2′ to be connected and the pins l4, l4′ to be free.
[0015] Figure 2 is a simplified diagrammatic view of a lampholder in which only the unsafe type of misconnection, mentioned above, is physically prevented. The lampholder includes a mounting portion 28, which may be of any convenient shape, and a flat base portion 30 against which one end of a fluorescent tube is to be placed. Two sockets 32, 34 are provided at a spacing S (approximately l3mm) suitable for receiving the pins l2, l4 or l2′, l4′ of a fluorescent tube, and the electrical connections are arranged so that the socket 34 connects to the starter-switch side of the circuit and the socket 32 connects to the mains side of the circuit. The base portion 30 has an outer free edge (that is, an edge just beyond and rearward of which there is no material which would prevent a pin from being positioned there) which is generally parabolic, hyperbolic, or of some other similar or other shape. The edges near the mounting portion 28 may be straight as indicated by the dotted lines 36 or cut away in a generally circular arc as indicated by the dotted lines 38. The shape of the base is arranged so that any part of the free edge of the base is further away than the spacing S between the sockets 32, 34, so that it is impossible for one of the pins of a tube to be inserted into the socket 32 while the other overhangs the edge of the base 30. The distance between the mains socket 32 and the mounting portion 28 may be less than S if the mounting portion is suitably shaped so that it would foul the free pin if the user attempted to insert the other into the socket 32. The distance between the starter-switch socket 34 and the edge of the base, on the other hand, is not critical, and may be as small as desired.
1. A fluorescent tube lampholder having first and second sockets, with first and second
electrical contacts therein, arranged to receive first and second identical pins of
a fluorescent tube, the lampholder being so shaped that one pin can touch the first
contact when the other pin is not in the second socket, but that one pin cannot touch
the second contact when the other pin is not in the first socket.
2. A lampholder as claimed in Claim l in which one pin cannot touch the second contact
when the other pin is not in the first socket because the other pin is fouled by a
part of the lampholder.
3. A lampholder as claimed in Claim 2 in which the said part of the lampholder is
a substantially flat base within which are the openings to the sockets.
4. A fluorescent tube lampholder having a substantially flat base arranged to receive
the end of a fluorescent tube, and within which are first and second sockets having
first and second electrical contacts therein and arranged to receive first and second
identical pins of a fluorescent tube, the minimum distance between the first socket
and a free edge of the base being less than the distance between the sockets, and
the minimum distance between the second socket and a free edge of the base being greater
than the distance between the sockets.
5. A lampholder as claimed in Claim 4 in which the free edge of the base is generally
parabolic or hyperbolic in shape.
6. A lampholder as claimed in Claim 4 in which the free edge includes generally parallel
edges in the vicinity of the second socket joined by a curved connecting edge in the
vicinity of the first socket.
7. A lampholder as claimed in Claim 4 in which the free edge in the vicinity of the
second socket is generally circular.
8. A lampholder as claimed in any one of Claims 4 to 7 in which the lampholder includes
a mounting portion.
9. A lampholder as claimed in Claim 8 in which the mounting portion is nearer the
second socket than the first socket.
l0. A lampholder as claimed in Claim 9 in which, in at least certain positions of
the tube, one pin cannot touch the second contact when the other pin is not in the
first socket because the other pin is fouled by the mounting portion.
11. A lampholder as claimed in any one of the previous claims in combination with
an electrical circuit for operating a fluorescent tube, in which the first electrical
contact is connected to a starter switch circuit and the second electrical contact
is connected to a mains supply lead.
12. A fixture for a fluorescent tube including a lampholder as claimed in any one
of Claims l to l0 in which the first electrical contact is connected to a starter
switch circuit, and the second electrical contact is connected to a mains supply lead;
and including means for attaching the fixture to a support.