Hi, this is my first post in this beautiful lighting site and, because there are a lot of people that know much more than me about lighting, i ask your help.

A lot of years ago, my grandmother tried to show me some 8mm films, but suddenly lamp
stopped working 
Some days ago, i asked her if i could fix her vintage projector and, when i opened it, surprise!
it have an sylvania tru focus lamp with 2 filaments inside. 

According to http://www.lamptech.co.uk/Spec%20Sheets/IN%20P%20A1-24%20Atlas.htm that is an similar 120v lamp,
i want to replace this vintage lamp with modern hid/led bulb (don't shoot me, because i don't want to waste another vintage lamp).

I'm thinking about led, because i can get some at relatively low prices (with resistor ballast, they are very reliable).
I thought also to gu10 mini cdm lamps, but i don't know what kind of equipment requires and how much i have to spend.

Because bans, heat and internal size, i can't use halogen with reflector.

Does anyone have suggestions? 

If I understood well, it is a movie projector, so you can not use any lamp, witch flicker (even on 100/120Hz), so MH with magnetic gear won't work.
The Atlas lamp you had there delivered 3100lm in rather small area (the filament), what is quite bright lamp.
The MH may work there, but rather some quartz one (ceramic arctube diffuse the light, so it is not as bright), so more some automotive type (from some "HID upgrade kit"). They come with an electronic ballast, you have to find only some 12..15V/90W DC supply (100W is necessary for short time before the lamp warm up, as the automotive ballast boost the power for short time on cold lamp), an "universal 15V/90W notebook adapter" would work.


LED would be way more tricky, as it is not as intense as the filament and need explicit heat sinking (as it does not emit the waste heat with the beam). So you won't be able to reach the original projector brightness (larger power LED's have larger emitter size, what would not be as useful for you, as the optics would use only small area from that). So the only candidate I know about are the SSC P7 or Cree MC-E. Both emit about 700lm, yet still all of that is in the small ~5x5mm rectangle (so it could be quite efficently focused to the film window).
Other problem would be the optic style. It's function is to project the filament image on the film window (it is slightly off-focus, so filament turns are blurred out) so, the beam then go to the main focus lens.
The original filament bulb light in all directions, so a reflector optics work well, so it is mostly used with incandescents (part of it is already inside the bulb).  But this rteflector optics utilize mainly the light coming from sides of the filament (from the beam direction),  where most LED's do not emit as much light.
So LED's would need refractive optic (a lens), utilizing the light emitted ahead from the LED chip (where most of the LEDs emit the most).
SO I guess converting to LED would require modification of the optics too.
On the other hand as the LED heat is carried out by the heatsink, it does not contain the IR (so heat) in the beam, so does not load the film by that, what would mean less danger for the (even rarer) films.

The LED need a constant current source:
The SSC P7 about 2.5A (it is rated for 2.8A, but that is really on the edge), while the drop is about 3..4V. The simplest power source would be stabilized 5V/3A with series 0.8Ohm/10W drop resistor (8 pieces of 3.9Ohm/2W in parallel would do the job).
The Cree MC-E could be supplied either in parallel, or series combination. I would guess the series would be more convenient, as it mean lower current. In that case the voltage drop would be about 12..16V and current about 0.6A, so easiest would be the constant current 0.6A/10..20V LED supply unit, or 18V notebook adapter with simple LM317 as a constant current regulator (see the LM317 datasheet)

The key for projector lamp substitute is the same shape of the light emitting part in the lamp, and same alignment of it to the mirrors and lenses as the original lamp

Besides that, you want :

Brightness - to not have too dark image

Power (not higher than the original lamp) - to not overheat and damage the projector or slides

Optical control - Light spilled in the projector contains IR. If light is hitting a part that is not supposed to be exposed to direct light, you can overheat and damage it in seconds

Size - to fit in and not be too close to stuff that can overheat

Voltage and socket type - same as the original lamp if you want to avoid modifying the projector



Some standard types of projector lamps are manufactured today too, so you can go look for a compatible lamp (maybe overhead projector lamp) or one that will require minimum of modification to the projector (such as only replacing socket). Note that some projectors use odd voltages so you may have to replace the transformer that powers the lamp too

HID lamp, specifically small ceramic metal halide lamps (such as CDM), have small light emitting part (arc tube) which is different shape but comparable size to the original incandescent lamp of most projectors. That means that if you position it perfectly in the projector, you can expect quite good performance. HID has advantage of many times higher efficiency than incandescent (even than projector incandescent, which have >20 Lm/W and 25 hour life) as well as whiter light and longer lamp life - your lamp takes less power, heats less, is brighter, and gives pure white light, and you dont have to worry about lamp life. The problem is fitting the ballast and ignitor in the projector (magnetic ballast can be made remote, electronic cannot, the ignitor usually cannot) as they take quite some space, the ballast heats, the ballast (especially the electronic) and ignitor can be damaged by overheating if too close to the lamp

Some auto lamps (need 12V with few A, you can get that with a ATX computer power supply) have a side reflector in them, but it is by far not as good as the real lamp - the light will get spilled, and heat along with it - you can damage the projector if there are any plastic parts in the lamp chamber or paint that can peel. Otherwise it can work (and even with non directional halogens), but probably be very dim

LED can be a good option as it is simple to use and efficient (comparable efficiency to the metal halide), but it is usually not bright enough for a point light source (the bright LED lamps have multiple light source points not one)



LED and metal halide would be best (if you cannot find a suitable reflector lamp) as they give out less heat for the same amount of light, so you can worry less about overheating and damaging the projector

Most projectors use a parabolic miror behind the lamp, but if your lamp is like what you linked too, then maybe the projector does not have it. So you may have to substitute something for it - either to get more light or to protect the lamp chamber back wall from overheating. Perhaps you can try keeping the old lamp in the projector and aiming light at it from another lamp, to use its internal reflector. Though you won't be able to focus it corectly in the reflector (you can't put the light source inside the lamp....)



I would go with the metal halide lamp, though probably not a CDM. There were some successfull attempts here to run 20W metal halide with 18W fluorescent ballast, that would save you some cost on the ballast, and 70W metal halide has its own magnetic ballast that is cheaper and more reliable than electronic - And the 70W halide makes so much light that you'll have lots of it even without proper reflector, while still making less heat than the original incandescent

If using a halide, use one with internal safety tube on the arc tube. Such lamp won't explode (and damage the projector) when it burns out

thank you very much for the answers.
for leds i thought something about bridgelux or cree xlamp cxa2011, because i used this for general lighting with some success.
for xenon headlight, i can use an boxed cheap atx power supply, but this can be tricky because bulb base size.

now, can someone tell me if this lamp is focused or create an straight parallel beam?

Projector lamps are focused so, the whole film window is evenly and as much as possible illuminated by rays coming in such direction, than they continue (more or less attenuated by the film picture) to the main projection lens and to the screen. That practically mean the optics should project the filament somewhere between the film window and the main projection lens.

So one option is to use an ellyptical reflector, where in one focal point is the lamp filament and close to (to be slightly of focus, so the filament is not sharply visible) the second focal point is the film window.
And another option is to use spherical mirror (to project back side radiation to virtually the original filament place) and then a lens to project the filament (both the "true" one, as well as the reflected one) to the film window.
This method is quite "LED friendly", as you place the LED in the place of the filament, facing the lens. Reflection is not necessary, as the LED does not shine backwards.

Other option is first form the parallel beam and then use the lens to focus it into the film window.


So one of these methods (or some similar) is already used in the projector and if you want to use source with different characteristic, you would have to modify it.

thank for the aswers.
now i have an idea about system:
1x cree mce 6500°K @700ma (it isn't warm white, but it it have 1.34 lumens than 3200°K version).
1x 15° optical reflector.
1x converging lens (to be decided).
1x 13.8v transformer with limiting resistor.

any suggestion?

Welcome to the site!

update: happy easter!
today i received my grandparent projector for replace the bulb.
Actually 6500°K led is too much cold, so i'm looking for lower cct led.
In an dark room, 8mm film is clearly visible also with an low power led, so i can search for other leds.

p.s. anyone have brownie 8 mod. a 15 g electrical scheme?
the bulb seems to be in series with projector motor.

update2:
Today i fixed the projector.
I used an common 3W 12° led spot; it seem work fine, but now i need to find a way to reduce voltage to the motor without using an halogen lamp.

Does anyone have suggestions?

If thats AC circuit, perhaps you can use some choke (wire should be thick enough for the current, low voltage circuits usually have high current)

Otherwise replace the PSU with one that gives the correct voltage

If thats AC circuit, perhaps you can use some choke (wire should be thick enough for the current, low voltage circuits usually have high current)

Otherwise replace the PSU with one that gives the correct voltage

i tried 150w halogen as ballast, with good success.
Because i'll return the projector to my grandmother, the halogen solution isn't applicable, so i'm using an 230v to 110v transformer, with very good results.

As my previous calculations:
230v main, 1.2A
- 125v 150w (1.2A) lamp
- 40Ω resistor (for voltage selection)
- 75V on motor

Actually, with transformer,
230v main, 0.xA
- 105V 0.67A at the transformer output
- 25V drop on 40Ω resistor

now, the motor is feed by 80vac, but current is much lower than original.
The problem may be power dissipation in resistor, but it don't get very hot.
The transformer don't get too hot, so i think it is in safe operating area.

As long as the motor is powefull enough that it can't get stuck, its ok even if its somewhat underpowered

thank for the assistance, Ash! 
When i have some time, i'll post picture about the bulb and the fix.