referring now to fig1 and 2 , the already existing slide projector 10 , in particular the kodak ektagraphic iii includes the carousel 11 holding slides 12 . the slide projector , the details of which are incorporated by reference herein , has suitable controls such as the focusing knob 18 for lens 14 , on - off power switch 15 , forward button 16 and reverse button 17 . along one side 10a of the projector 10 is disposed the cooling air vent 19 as well as access door 20 for a space internal of the projector 10 wherein a lamp module 21 is received . the lamp module 21 houses a projection lamp 22 , the light from which is reflected off mirror 23 and thereafter through heat glass 24 and condensing lens 25 so that the image contained on slide 13 in the position shown will pass through projection lens 14 and appear on a remotely positioned screen . in accordance with the present invention , the lamp module 21 is removed from the projector and in its place , the automatic lamp changing unit 30 is provided which includes a housing 31 having an air passage 32 therein for receiving the air through the vent 19 of the projector , an automatic lamp changing unit 33 which has one of the three lamps therein positioned on the light path of the originally existing module 21 so that the light therefrom passes directly through the slide and to the lens 14 . in order to isolate the lamp heated air , a tunnel made of a suitable metal tube 34 is provided which abuts against the lamp unit 33 as shown , while not restricting the passage of light . the unit also comprises the insertable portion 100 which is received in the space in projector 10 normally taken by module 21 . the portion 100 includes bracket members 103 , 104 ( see fig3 ) for holding a replacement lens 25 and heat glass 24 as well as power pins 101 , 102 , referred to hereinafter . as a result of the positioning of each lamp in an operating position as shown , there is no mirror needed in the optical path . the automatic lamp changer 30 is also provided with means for connecting to the access door lock of the projector so that no modification need be made to the projector 10 in order to operate with the automatic lamp changer 30 and therefore the projector 10 can be brought back to normal by merely disconnecting the automatic lamp changer 30 and reinserting the module 21 . the lamp changer also includes a vent opening 36 for venting the cooling air from the fan of the projector . baffle 35 prevents excessive light leaks from the automatic lamp changer while permitting the excape of hot air . moreover , the electrical connection to the automatic lamp changer 30 can be obtained from the connector pins 101 , 102 ( fig3 ) which engage the existing projector connector normally used to connect power to the module 21 , to provide all of the power for lamp changer 30 . referring now to fig3 the automatic lamp changer is shown with its important elements in an exploded form . the housing 31 includes the frame 31a to which a front plate 39 is connected which has the cut - out 32 for the cooling air from the vent 19 as well as the circular opening 39a in the light path for receiving the tunnel 34 . the housing also includes the back plates 37 and 38 . the back plate 37 is used to mount electrical components ( not shown ) and is mounted onto frame 31 by conventional screw connection . plate 38 is connected by an easily removable releasable mechanism in order to facilitate the access to the lamp mount 33 when lamps have been burned out and need to be replaced and includes locking key 41 which passes through aperture 42 and aperture 43 in bracket 44 connected to frame 31a and which engages a locking clip 45 mounted thereon in a conventional manner . in this way the cover plate 38 is easily removable without the need for any tools . in order to enable the automatic lamp changer to be connected in place with the projector , the lock mechansism 50 is provided . this lock mechanism is configured to engage with the access door lock on the projector so that the automatic lamp changer will be reproducibly clamped in place each time . the locking means 50 includes lock member 53 which is bolted to the front plate 39 by suitable screw fasteners 80 . the clamping effect is carried out by member 51 which is slidably mounted to plate 39 biased downwardly by spring 55 and pulled upwardly into the locking position by screw 54 . the locking means 50 engages the access door lock by means of the lip 51a . the remaining hardware shown in fig3 constitutes the mounting for the lamp mount 33 as well as the linkage and electrical elements needed in order to effect a lamp changing when desired . in accordance with u . s . pat . no . 3 , 914 , 645 , the lamp mount 33 , although different from the lamp mount construction shown therein , is controlled in a similar manner and by similar circuitry and switching elements . a photocell ( not shown ) senses when there is less light than is proper for a given input voltage for the lamp in the operating position . the signal from the photocell is sensed by an electronic circuit such as that used in the aforesaid u . s . patent for producing a signal which energizes solenoid 61 . solenoid 61 releases linkage 62 which is biased by spring 63 and allows the lamp mount 33 to turn . the lamp mount turns as a result of the torsion spring mounting which includes torsion spring 65 and torsion spring holder 66 which is mounted in aperture 67 of the front plate 39 . the mounting of the spring is similar to that shown in the aforesaid &# 39 ; 645 patent . the sector thereby rotates to within a very short distance of the next lamp position at which point link 64 engages detents 71 or 72 ( see fig4 ). after a few seconds time during which the filament of the lamp now approaching the operating position stops vibrating , the solenoid 61 is deactuated causing link 62 to reengage the detent 72 prior to link 64 being drawn out of engagement with detent 71 , thereby permitting lamp mount 33 to reach the final advanced position of the lamp mount sector . the switches 68a - c provide energization to the proper one of the three lamps and deenergize the others . fig4 shows the lamp mount 33 in exploded form and comprises the lamp disk 81 having apertures 81a - 81c which abut against tunnel 34 , lamp holder 82 which has the equivalent three apertures 82a - 82c and corresponding lamp mounting portions 83a - 83c which hold lamp clips 84a - 84c of which only 84b and c are shown and to which also is connected the top plate 85 which holds lamp sockets 86a - 86c . by means of hinging element 87 which is pivotally mounted on ears 88 of disk 81 by screws 89 , the plates 82 and 85 may be pivoted rearwardly to expose the lamps for removal . over - center springs 91 , engaged by pin 92 and hooked in holes 91a in top plate 85 hold lamp holder 82 firmly in its operating position or , during lamp replacement , in its open position . it will be appreciated that the instant specification and claims are set forth by way of illustration and not limitation , and that various modifications and changes may be made without departing from the spirit and scope of the present invention .