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Converting a projector from incandescent to solid state?

chopnhack

Apr 28, 2014
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My parents have unearthed an old 35mm slide projector along with literally thousands of slides. After watching a few hours, the bulb of course blew the next day when they went to view some more. They asked me to find a replacement bulb which I did, but at some outrageous prices. New bulbs ~$56 shipped, and get this: stated life hours ~25 :eek:
Back in the day when these devices were common, the bulbs were fairly reasonable, I am sure, but economy of scale being what it is, they are expensive now.

The bulb in question outputs 1000 lumens and is rated for 500w at 120v.

Would I be able to use a LED or other type of bulb in its place? I was thinking of those 50w and 100w LED chips.
As for interface, I would probably use the bulb base to use as an attachment point for wiring. I assume I would need a driver as well.

Thanks in advance for your collective thoughts.
 

(*steve*)

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A LED would be able to provide the same amount of light at the cost of far less heat.

However you need to be aware that the optics are designed with a particular lamp in mind, so you may get uneven lighting or other issues if you don't take that into account.

Having said that, I think a 50W LED could be used, and would only need to be operated at perhaps half power or less.

You will need to provide some heatsinking to ensure that the LED doesn't get too hot though.
 

chopnhack

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However you need to be aware that the optics are designed with a particular lamp in mind, so you may get uneven lighting or other issues if you don't take that into account.

Having said that, I think a 50W LED could be used, and would only need to be operated at perhaps half power or less.

You will need to provide some heatsinking to ensure that the LED doesn't get too hot though.

Excellent point steve! The tip of the bulb is frosted at its top, presumably to get more light to exit around the middle. I don't know what the compartment looks like, but I would imagine that its lined with reflectors of some sort.

Why do you think it would only need to be operated at 1/2 power? Should I be looking to simply match the lumens or should I get more lumens than needed since the optics are going to be different?

Thanks!
 

hevans1944

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A 35mm slide projector typically has two plano-convex lenses, with the convex surfaces facing each other, to form a condenser lens assembly. The lamp filament is positioned so its magnified image fills the entrance pupil of the projection lens. You may have to fiddle with an LED lamp to get it positioned properly.
 

KrisBlueNZ

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Wouldn't you rather have those slides as digital images? Google slide scanner, or slide scanning services.
 

hevans1944

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My eldest daughter borrowed my 35mm slide collection last year and had someone scan and store the results on a compact disc. Too bad she forgot to send me a copy, but I did get the original slides back... <sigh> I have an HP and and Epson scanner so I can do this myself. Excellent suggestion @KrisBlueNZ .
 

KrisBlueNZ

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My eldest daughter borrowed my 35mm slide collection last year and had someone scan and store the results on a compact disc. Too bad she forgot to send me a copy
How rude! It only takes a few minutes to copy a CD :-(
 

(*steve*)

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Why do you think it would only need to be operated at 1/2 power? Should I be looking to simply match the lumens or should I get more lumens than needed since the optics are going to be different?

Possibly now moot, but here goes:

I was recommending that you have approximately the same number of lumens. I was assuming an output efficiency of something less than 100 lumens per watt, and therefore thinking that you'd need to drive it at less than 1/2 power to get 1000 lumens.

Operating these LEDs at a lower than rated power will make them last longer and mean you have far fewer heat issues.

A limit on brightness for a slide projector is the amount of heat generated by the bulb. So going brighter with a LED source should be fine.

The colour of the LED source will not be the same as the bulb. Determine the colour temperature of the original (possibly 3200K) and compare that to the potential replacement. "Warm" can vary from 2600K to 3500K, and "cool" from 6000K to perhaps 9000K. If you can get something with a known colour temp, then from 3000K to 3500K should be fine (If my assumption about the projector lamp is correct).
 

BobK

Jan 5, 2010
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Are you sure it is only 1000 Lumens? That is less than a 100W bulb and you say the bulb is rated at 500W. I would wonder why it would be so inefficient, particularly when heat is a problem with a projector.

Bob
 

chopnhack

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Are you sure it is only 1000 Lumens? That is less than a 100W bulb and you say the bulb is rated at 500W. I would wonder why it would be so inefficient, particularly when heat is a problem with a projector.

Bob
Its an old projector, the bulb is a DEK 500w, 120v rated at 1000 lumens. I assume that since it is incandescent the majority of the energy is wasted in heat and internal resistance of the bulb.
 

hevans1944

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chopnhack

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Amazon has this projector lamp for sale at $37.74 with free shipping. Arrives before Christmas if ordered now.

The 1000 lumen rating may be the illumination of the projector. There is a lot of light lost in the condenser lens (usually there is an infra-red blocking filter between the condenser and the slide) imaging the lamp filament to fill the entrance pupil of the projection lens, plus more light lost in the projection lens optics.

Thank you Hevans! I sent my father two links of some old stock late last night. One was going for around ~$6 shipped which was an incredible deal. The other was double that, still a phenomenal value if they function. I just thought that for the money, there certainly wasn't enough life span for viewing, that is what got me thinking about converting to an LED.
 

hevans1944

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At work, back around 1997 or so when I first started there, I found a really ancient projector that was used to illuminate microscopic dust motes in the air over a "clean bench" used for semiconductor wafer processing. The bright collimated light from the projection lens made the motes sparkle. See sparkle? Time to change the air filter.

Well, the folks involved in that project had long since moved on to greener pastures, leaving the projector and other assorted toys behind, like a resist spinner, a wafer washer, ion generators, and two clean benches with HEPA filters and big blowers. After awhile I got around to playing with the projector, but some short time later the lamp burned out. Like you, I found a replacement at exorbitant cost. So I didn't buy one, waiting until I could find a use for the projector. The projector sits on a shelf in my office today, unused and un-lamped, awaiting a purpose.
 

chopnhack

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At work, back around 1997 or so when I first started there, I found a really ancient projector that was used to illuminate microscopic dust motes in the air over a "clean bench" used for semiconductor wafer processing. The bright collimated light from the projection lens made the motes sparkle. See sparkle? Time to change the air filter.

Well, the folks involved in that project had long since moved on to greener pastures, leaving the projector and other assorted toys behind, like a resist spinner, a wafer washer, ion generators, and two clean benches with HEPA filters and big blowers. After awhile I got around to playing with the projector, but some short time later the lamp burned out. Like you, I found a replacement at exorbitant cost. So I didn't buy one, waiting until I could find a use for the projector. The projector sits on a shelf in my office today, unused and un-lamped, awaiting a purpose.

That is awesome Hevans, it almost sounds like this thread is (maybe?) inspiring you to hack an LED into the projector? :D
Sadly, I will have to live vicariously through you - my father gave it to my uncle a few days ago... Apparently it was his to begin with! I can't tell you though of how many decades I can recall this projector being in our garage :rolleyes:
 

hevans1944

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That is awesome Hevans, it almost sounds like this thread is (maybe?) inspiring you to hack an LED into the projector? :D
Sadly, I will have to live vicariously through you - my father gave it to my uncle a few days ago... Apparently it was his to begin with! I can't tell you though of how many decades I can recall this projector being in our garage :rolleyes:
No projector LED hacking for me. I prefer digital images I can access from my Galaxy 5 smartphone, my laptop, or my desktop computers. Whenever I buy a scanner I always make sure it can scan transparencies, particularly 35mm color positives and negatives. I do like bright white LED replacements for incandescent lamps around the house.
 
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