This Instructable presents an improvement of a project posted in 2013 by Openproducts: ‘Fixed Slide Projector With Low Energy Consumption’ (CC BY NC SA).
In that 2013 Instructable the 150 W (24 V, 4500 lumen) halogen bulb of a conventional slide projector was replaced by a 14 W (12 V, 205 lumen) halogen bulb in order to arrive at 91% energy saving (this calculation includes fan powering and adapter losses) and a reduction of the light yield by 95%. Basically this project was a power downsizing of the slide projector.
In this new Instructable (November 2018) the original halogen projector bulb is replaced by an LED spotlight, which introduces more efficient technology. The LED spotlight has a power consumption of 5 W and a light yield of 350 lumen: power consumption is reduced by approximately 98% at a reduction in light yield of around 92%. With the LED light the projector is still sufficiently powerful to show a picture on a wall.
The main questions answered in this Instructable are:
Is an LED spotlight pointed enough to act as a slide projector lamp? (Answer: yes)
When opening an LED spotlight, will it still function? (Answer: yes)
Does an LED spotlight give a sharp projected picture? (Answer: yes)
The LED spotlight in question had one visible LED, but after opening it appeared that internally it consisted of four individual LEDs, with bridges between them. These bridges were optically cancelled out by the lenses in the slide projector. Also, it was found that opening the LED spotlight did not influence the functioning of the LED spotlight: there is no protective atmosphere in the LED (like there is in conventional light bulbs). And finally, it was found that the projected picture is pinpoint-sharp.
The next steps elaborate on the above findings in more detail.
Safety notice: in the LED rebuild the lamp cooling fan is omitted, which cancels out the typical noise made by a slide projector. However, a powerful LED spotlight develops quite some thermal energy. Be sure to allow for enough convection around the LED spotlight in order to cool the lamp. It’s a good idea to perform a long duration test to see whether temperatures remain acceptable. It’s recommended not to leave the projector switched on unattended.
Step 1: Choosing the Right LED Spotlight
In a slide projector, the light source should be exactly in the focus point of the lenses. Therefore, the LED spotlight should consist of a single LED. Chosen was a 230 V - 5 W - 350 lumen - GU10 LED spotlight.
Step 2: Removing the LED Spotlight Diffusor
The lens in the LED spotlight serves to make the LED light more diffuse. That’s exactly what one doesn’t want in a slide projector, so this lens was removed by gently pulling the closing ring out of its position.
Step 3: The LED Spotlight Appears to Have Four Individual LEDs
After opening the LED spotlight it became clear that internally it consists of four individual LEDs. This was demonstrated by projecting the LED beam through a magnifying glass (using the Colander Effect Lamp, see Step 6 below), which clearly shows four distinct sections. When using the LED spotlight in the slide projector, the four section are not noticeable anymore, thanks to the optical characteristics of the projector.
Step 4: Replacing the Conventional Bulb by the LED Spotlight
The light point in the slide projector is exactly in the focus point of the lens. The LED should be positioned exactly on the same spot as the filament in the original halogen bulb. As can be seen from the pictures, the dimensions of the LED spotlight fit nicely to the available space inside the projector.
Step 5: Judging the Projected Picture
The projected picture looks nice and sharp. The LED spotlight has a warm color (2700 K) but it is certainly not strong enough to project a picture during daylight. However, in the half-light it will work fine, and the projection will be at its best in the dark. An important benefit of this slide projector modification is that no fan is needed anymore, which makes the device soundless.
Step 6: Another Projection: the Colander Effect Lamp
The Colander Effect Lamp is another Openproducts Instructable that uses an LED spotlight in a projector, this time using a magnifying glass, as indicated in the pictures above.