Reading Illuminance (Lux) from a Light Sensor (VCL) — Delphi Source Code Collection

Create the Project and Design the Form

Launch Delphi, then select File → New → Windows VCL Application – Delphi (W) from the menu.
Drag and drop two TButton components and one TEdit component onto the form.

Entering the Source Code

Add the following source code to the event handlers such as Button1.OnClick, Button2.OnClick, and Form1.OnDestroy.

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls,
  System.Sensors, System.TypInfo;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    LightSensor:TCustomLightSensor;
    procedure LightDataChanged(Sender:TObject);
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var SensorManager:TSensorManager;
    i:Integer;
begin
  //Get the sensor manager
  SensorManager:=TSensorManager.Current;

  //If the sensor manager is supported
  if SensorManager.CanActivate then
  begin
    //Activate the sensor manager
    SensorManager.Activate;
    //Loop through all sensors
    for i := 0 to SensorManager.Count-1 do
    begin
      //If a light sensor is found
      if SensorManager.Sensors[i].Category = TSensorCategory.Light then
      begin
        LightSensor := TCustomLightSensor(SensorManager.Sensors[i]);
        LightSensor.OnDataChanged := LightDataChanged;
        //Enable the sensor
        LightSensor.Start;
        Edit1.Text := Format( '%5.0 fLux', [ LightSensor.Lux ] );
      end;
    end;
    SensorManager.Deactivate;
  end;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  if assigned(LightSensor) then
  begin
    LightSensor.Stop;
    LightSensor := nil;
    Edit1.Text := 'Stopped';
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  if assigned(LightSensor) then
  begin
    LightSensor.Stop;
  end;
end;

procedure TForm1.LightDataChanged(Sender: TObject);
begin
  Edit1.Text := Format('%5.0f Lux',[LightSensor.Lux]);
end;

end.

Run the Application

Select Run → Run, or click the debug run button to compile and start the application.
When you click Button1, the light sensor will be activated (if your PC is equipped with one), and the illuminance value will be displayed in lux.
Clicking Button2 will stop the sensor.