Class 153 CDL interlock lights

[lillita]

A friend of mine was recently onboard a Class 153 and got a picture of a CDL panel a guard had left open. We noticed that the section labelled 'Door interlock' has three indicators.



We have both searched for hours trying to find an answer online to no avail, so I'm hoping an answer might be found here: Do these all show the status of the interlock circuit, or do they have individual purposes?

Thank you!

 

[causton]

I believe it is failsafe in the sense that all lights should illuminate, therefore if one bulb fails the status will still be shown correctly.