From halogen bulb to LED
What if one could increase the lamp life 100-fold, and avoid all that heat – that would burn the film in case the film would stop running…
3 generations were seated to dig into a number of film rolls from my childhood, to travel back in time some 40 years. We got through 20 minutes of film, when the light bulb came to an end.
The projector – the patient
Life expectancy is 25 hours, so having lasted since my childhood – that in itself was a lot of hours than the listed expectation.
Anyway, this got me starting to think about a conversion to modern LED lamp. I had seen conversions on youtube of modern movie and presentation projectors – so why not try the same on a 8 mm projector. A new bulb would cost about 35 €… for only ~20 hours!
- Available space
- Kelvin temperature
- Height of light stream, bulb focus center
As I did not find a manual of the 8mm projector, I had to rely on photos from the internet and what my father sent me – we live in separate countries. Internet holds plenty of replacement (halogen) data on bulbs, so the original lamp dimensions and light performance data was easy to find.
But not how much space I would have at hand for a new lamp solution. Photo on the right is from a similar projector – one of the few I could find, actually, that shows not only the halogen lamp in place, but also with an open door (!) :
I would have to build a lamp holder, to keep the lamp fixed in place – but also to have the light stream centered at the correct height – into the lens system. Available space is basically 50mm in cube. Although, height-wise from the lamp base, some 80 mm available.
The light ‘color’, warm of arctic, is a matter of taste. However why not get as close as possible to the original design – being 3200 K. This is almost smack center in the spectrum between warm or cold color, meaning yellow or arctic light, where 6000 K is cold.
One of my personal driving forces was to digitize the 8 mm films, through the use of a digital HD camera. To go ‘old school’ as well as low budget. Not utilize (spend money) on a conversion unit, a module that the film is run through, nor a professional service center.
I learned that modern digital recording cameras auto-correct on the Kelvin value. Thus from the perspective of digitizing, one doesn’t need to take great care in matching the color temperature.
Lux, or lumens is the strength of light emitted. Not to be confused with the bulb power consumption – which in this case of the halogen bulb was 50 Watts (W).
The data I retrieved on the halogen bulb
- Projector Lamp : 8V, 50W, 6.25A, Tungsten, Reflector housing
- Sockel : P 30 S, A1 / 17 (LIF)
- ANSI : CXR / CXL
- Bulb Shape Details : RT14
- Base: P15S30 single contact – 15mm Pre-Focus Collar
- Life: 25 hours average
- Kelvins: 3200
- Luminous flux: 36 lm
- Bulb Shape: T9.5
Selected lamp runs at 8 V and doesn’t produce any heat. At least not more than that possible to hold in hand. The lamp is rated at 12 Volts, however runs fine at 8 V. It holds inside itself a switching unit, meaning it doesn’t matter how the wires are connected to it, in DC. Which makes me think it doesn’t care if if it is AC or DC (which the package actually specifies).
- 500 candela
- 230 lm, @ 36º
Having worked out how to fasten a structure to the old halogen lamp base, as well as knowing how the LED lamp looks like, and at what height the lamp should be located at, remaining was to figure out a suitable structure ‘in between’.
Utilizing SketchUp, a 3D model came to life. My very first project in the field of 3D printing, by the way. Printing robots exist at my local library, where I also received great help. Took some 4 hours to print, as far as I remember.
Performance of LED
To the eye, we were all surprised at how well the film was projected onto the wall. The lamp performed really well, I must say. I noted that I could have closed the lamp housing altogether, as no heat needed to be vented. Thereby keeping the room totally dark, wherein only the light emitted would be from the projector lens.
I was less pleased with how the recorded quality came out, when watching on TV. Especially where the light strength was weak in the film – for example if scenery was in sunset or back light, the recorded material was in low contrast. Perhaps due to the light emitted from the projector housing. Thus, a few lessons were learned.
If I would do the conversion again, I would focus on improving the following items.
- Seal the light from escaping the “light-room” into the room. As can be seen from above, there’s a gap of about 10 mm. Would improve the recorded contrast.
- Increase the power supply to specified 12V.
- Find a slightly stronger LED lamp, with a more centered beam (light stream). Perhaps a LED complete with its housing of a high power LED torch.
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About the author
Martin R.C. Andersson started out as a mechanical engineer, slowly developing a soft spot for project management in which he worked 10 years.
Although having resigned from a corporate career within project management, the soft spot he keeps alive through a keen interest in room environment treatment. By control of sound and light, looking to tweak for that noise-free listening… which should be a norm.
Values silence, and now and then solitude.
Thinks Mindfulness is a ‘state of being’ – a flow, zone – when work gets done well.
When thoughts flow – without disruption – to reach either a creative state or finish what’s at hand.
When the outside world is tuned out, performance is tuned in.
Feels best when Minimalism, Functionalism and Art come together, crossing paths.