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So I'm planning on projecting slides made from color reversal film for a long continuous amount of time in an old fashioned slide projector and was wondering how much damage the heat from the projector lamp might cause the slide.

I already figured it would probably be a good idea to make a copy of the slide and use that so the original doesn't get destroyed. But in theory what are the risks if say I kept the slide in the projector and the projector turned on for a whole day?

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  • \$\begingroup\$ If the slides are irreplaceable then You could have some duplicates of the slides made and use them if you are worried about the light source on them for long periods of time. \$\endgroup\$
    – Alaska Man
    Commented Oct 15, 2019 at 16:40
  • \$\begingroup\$ E6 process? Probably, unless they are old Kodachromes. Also be aware that most projectors have multiple bulb options. The Kodaks that I used had 3: normal, bulb life was about 35 hours; Extra bright, bulb life only about 2 hours; Long life, can't remember how long, I never used them because they were dimmer. I am guessing that with a "normal" bulb you will see noticeable degradation in the slides after a day or two. It is probably best to run tests with your setup. But, I wouldn't run a projector unattended unless it was somewhere that couldn't cause a fire that would spread. \$\endgroup\$
    – Mattman944
    Commented Oct 15, 2019 at 17:09
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    \$\begingroup\$ I’d say that digital scanning/photographing the slides and projecting them using a laptop and beamer is the safest, most non-destructive and enduring option. Maybe you can record and playback the sound of a “classic” projector to enhance the authentic feeling a bit... \$\endgroup\$
    – agtoever
    Commented Oct 15, 2019 at 17:13
  • \$\begingroup\$ From my experience, less than a minute is already enough to damage the slide \$\endgroup\$
    – Jérôme MEVEL
    Commented May 5, 2020 at 13:51

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If possible: move to digital

My first thought is to move to digital: make digital scans or photos of your slides and use a digital projector and a laptop. One of the risks of a projector running 24x7 is overheating, with the possibility of a fire breaking out. Please be aware of that.

Also take into account that you'll need to frequently change the light bulb if you rely on the classic incandescent light bulb.

Ballpark figure: ~12 hours of illumination per slide

Researching into your question, I stumbled on this Tate Resesarch article on the conservation of slides. It is full of details and background stories. Highly recommended reading material. The introduction states:

With slide sets needing to be changed roughly every six weeks, a large number of duplicate slides needs to be provided for every slide-based work.

A rough calculation, based on a fully loaded carroussel of 80 slides, this is around 6 weeks * 7 days/week * 24 hours/day / 80 slides = around 12 hours of projection time per slide. This assumes 24x7 illumination, but also assumes a full carroussel. So this gives you a ballpark figure. You'll want to duplicate your slides long before that.

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    \$\begingroup\$ @Jeffrey This fits with my experience using these materials and equipment. Recommendation to go with digital display is good and valid alternative. \$\endgroup\$
    – Stan
    Commented Oct 15, 2019 at 19:16
  • \$\begingroup\$ You will of course need to spend quite a lot of money on a digital projector if you want to keep image quality comparable even to a cheapish slide projector. You may also want to consider that bulbs for digital projectors are usually much more expensive than slide projector bulbs, raising the operating costs per hour significantly. If this is a one-time project, it may still be easier and cheaper to make duplicates of the slides for projection. \$\endgroup\$
    – jarnbjo
    Commented Oct 16, 2019 at 11:35
  • \$\begingroup\$ I am making this the accepted answer as it gives a rough estimation of the degradation of slides in a projector. Just for everyones information: I am planning to use an old slide projector for more artistic reasons. It's not only about just projecting the images but about the way they are presented as well. Digitally projecting them doesn't serve the goal I am trying to achieve. Still you answered my question more than thoroughly. Thanks for all the effort you put into this! \$\endgroup\$
    – Jeffrey
    Commented Oct 20, 2019 at 21:45
  • \$\begingroup\$ since you mentioned it: Do you have any estimates on the life expectancy of these light bulbs on heavy duty? \$\endgroup\$
    – Jeffrey
    Commented Oct 20, 2019 at 21:46
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Are you speaking of continuously projecting one single slide, or projecting through a tray of 40 slides? Bad either way, but if one slide, you certainly better prepare many duplicate expendable copies.

Kodachrome is said to be the best long archival life if stored in the dark, but the worst about fading with continual projection. Fujichrome is said to be best about projected life, but which is still pretty short. Re: https://en.wikipedia.org/wiki/Kodachrome#Archival_stability

Specifically, see Table 6.1 (about 5th page) on http://www.wilhelm-research.com/pdf/HW_Book_06_of_20_HiRes_v1c.pdf

Also more: http://www.wilhelm-research.com/pdf/HW_Book_18_of_20_HiRes_v1c.pdf

Switching to show digital is the best advice.

(busybody edits: please do not edit these to be hidden links. My plan is that people should be able to see what they are about to click on).

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  • \$\begingroup\$ Thanks! That's also very useful information \$\endgroup\$
    – Jeffrey
    Commented Oct 20, 2019 at 21:47

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