RPM meter part name?

[fstnd]

I bought a 60 year old analog RPM meter and would love to restore it. It worked for a while, but then I broke the solder, I tried to solder again but messed up. Then I even lost it.
What is the name of the "lens" that is focused on the propeller? It operates at 7V.

 

[fstnd]

it looks very similar to this LDR

 

[Chubaka]

View attachment 235148it looks very similar to this LDR

Photo resister I believe

 

[fstnd]

Is there a way for me to know which one I need?

 

[Chubaka]

@WickedFog or @Greywolf74 might now. I use mine as a light sensor. When it gets dark my lights automatically come on.

 

[WickedFog]

I am not sure on those. But looking into it, they are designed for various light conditions, ie low light, bright light, etc. Without having the original to test the resistance of it, your left guessing. You could solder some wire leads on the board where the resistor mounts and test various resistors before soldering it in. That's all I got.