I have recently acquired an Ender3 V3 KE printer together with the light bar kit. Does anyone know if it is possible to obtain a logic level output from within the Ender3 firmware that would allow me to control the light from within the Creality Print app. which I run on my MacBook Pro? My current release of Creality Print is V5.1.2 9904. I am competent to design and make a suitable (relay) interface to switch the light On and Off.
I belive you can do it using Gcode but I’m no expert 
I found this on Reddit if that’s any help to you?
Thank you for responding. The problem is that the light bar, in accordance with Creality instructions, is wired into the 24V DC supply on the main board which is not unique to the light bar so I think any form of internal control of this supply is a non-starter. Like you I am NOT an expert on Gcode but even if a command existed the problem is how to access a suitable control output; just a cursory look at the main board does not suggest the existence of any uncommitted outputs. Perhaps I’ll just consider a simple light sensitive switch that turns the light bar on whenever the printer is on and it is dark. Thanks again for the response.