Changing a picture box visibility from C# code

So I tried to create a new form and reference it...the compiler didn't mind this but it clearly wasn't changing the visibility of my picturebox. this is how I was calling my method found in my form, FROM my c# script.

Form1 updateForm = new Form1();
updateForm.setLights();

It called the method, and seemed like it worked! Until I read a post about instancing forms, and how by creating a "new" instance of Form1, that anything referenced by my updateForm would not change what I would see on my Form1.

So what I need to do is to call the function in setLights() which is in my Form1, and get it to change the visibility of my image on that form, from my C# code. Please see below (i understand the issue of the instancing problem mentioned above, but I left it in so that hopefully it will give better insight into what I am "trying" to do :) ALSO, please keep in mind that setLightCall() is running in a separate thread. Thanks in advance!

This code is also in my main c# script, and is the main function that I use to call my threads

static void Main(string[] args)
    {
        Thread FormThread = new Thread(FormCall);
        FormThread.Start();

        Thread setLightThread = new Thread(setLightCall);
        setLightThread.Start();

        log4net.Config.XmlConfigurator.Configure();
        StartModbusSerialRtuSlave();
    }

This code is in my main C# script

public  void setLightCall(Form1 parent)
    {
        Form1 updateForm = new Form1();
        while(true)
        {
            updateForm.setLights();

        }


    }

The below code is in my form1

public void setLights()
    {
        Input1GreenLight.Visible = false;
    }

Copyright Notice：Content Author:「Pardon_me」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/25394756/changing-a-picture-box-visibility-from-c-sharp-code