Pretty old slide viewer. It belonged to my grandparents. I think from about the late 60’s. It worked with a battery and a small light bulb. We could play with it for hours and hours (for my feeling) but always the dia lamp had to be repaired. Now, years later, perhaps 40 years, I got the opportunity to repair it. All the inside stuff (a disaster: too thin cables, rotten connections) I took out, to convert the slide viewer to modern standards. I choose not to use batteries but attached a cable with an adaptor. For two reasons: The viewer doesn’t have to be opened to change batteries (it is still a quite vulnerable object.) Secondly batteries are bad for the environment. Actually I remember a third reason: The slide viewer stays bright, while a light bulb and battery give less and less light. Plus the led I used will shine almost forever… An extra feature is a switch on de backside of the lamp.