ESP8266 microchip is used to host a web server. This way we can control ESP's LED diode by turning it on or off with a web request, e.g., "http://192.168.0.16/switch".

LEDControlServer.ino

// This script is avilable as gist:
// https://gist.github.com/mikbuch/212cfb7365703caf517aa83642d10d91

/* Requirements:
 *  * "esp8266" board installed.
 * 
 * In order to install the board, go to:
 *   -- Tools => Board => Boards Manager => Install "esp8266"
 * It also includes "Wemos" boards ("LOLIN").
 * 
 * Then you set the board as:
 *   -- Tools => Board => ESP8266 => Boards LOLIN (Wemos) D1 lite
 * 
 * Now you can complie and upload the code to your Wemos board.
 */
 
 /* Connection status codes ("WiFi.status()"):
 *    0 : WL_IDLE_STATUS when Wi-Fi is in process of changing between statuses
 *    1 : WL_NO_SSID_AVAILin case configured SSID cannot be reached
 *    3 : WL_CONNECTED after successful connection is established
 *    4 : WL_CONNECT_FAILED if connection failed
 *    6 : WL_CONNECT_WRONG_PASSWORD if password is incorrect
 *    7 : WL_DISCONNECTED if module is not configured in station mode
 *
 * Source: https://arduino-esp8266.readthedocs.io/en/latest/esp8266wifi/readme.html#diagnostics
 */
 
/* Instructon on how to use this example on the client side.
 *  
 * The client side means that you will be sending requests
 * to the server hosted at ESP8266, and you will be receiving
 * requests.
 * 
 * Use a root request (e.g., http://192.168.0.22/), or either of
 * the two endpoints:
 *   (1) /switch (to switch diode), or
 *   (2) /status (to get the info about diode status: on or off).
 * For example: http://192.168.0.22/status
 * ----------------------------------------------------------------------
 * 
 */
 
#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WebServer.h>
#include <ESP8266mDNS.h>

/* SSID is the name of your WiFi network, e.g.: "linksys", or "ab8402932".
 * You have to set the variable STASSID below.
 * --
 * STAPSK is the password you your WiFi (WLAN) network, i.e., the password
 * to your router. This variable has to be set as well.
 * 
 * To sum up, the 4 lines below this block comment should look shomehow
 * like that:
 * 
 * #ifndef STASSID
 * #define STASSID "linksys"
 * #define STAPSK  "@sdjj2325k^#asd"
 * #endif
 */
#ifndef STASSID
#define STASSID "ssid"
#define STAPSK  "password"
#endif

const char* ssid = STASSID;
const char* password = STAPSK;

ESP8266WebServer server(80);

int led_status = 0;
 
void handleRoot() {
  Serial.println("Received a root (`/`) request.");
  Serial.println("LED status is: " + String(led_status));
  Serial.println("----------------------------");
  
  // Server response
  String message = "Use either of the two endpoints:\n";
  message += " (1) /switch (to switch diode)\n";
  message += " (2) /status (to get the info about diode status: on or off)\n";
  message += "For example: 192.168.0.22/status\n";
  message += "----------------------------\n";
  message += "LED status is now: " + String(led_status) + "\n";
  message += "----------------------------";
  server.send(200, "text/plain", message);
}

void handleLedSwitch() {
  Serial.println("Received a `switch` request.");
    
  if (led_status == 0) {
    digitalWrite(LED_BUILTIN, LOW);
    led_status = 1;
  } else {
    digitalWrite(LED_BUILTIN, HIGH);
    led_status = 0;
  }
  Serial.println("LED status is: " + String(led_status));
  Serial.println("----------------------------");

  // Server response
  String message = "Switched LED!\n\n";
  message += "Now status of the diode is: ";
  message += String(led_status);
  server.send(200, "text/plain", message);
}

void handleLedStatus() {
  Serial.println("Received a `status` request.");
  Serial.println("LED status is: " + String(led_status));
  Serial.println("----------------------------");

  // Server response
  String message = "Status of the LED is: ";
  message += String(led_status);
  server.send(200, "text/plain", message);
}

void handleNotFound() {
  digitalWrite(LED_BUILTIN, LOW);
  String message = "File Not Found\n\n";
  message += "URI: ";
  message += server.uri();
  message += "\nMethod: ";
  message += (server.method() == HTTP_GET) ? "GET" : "POST";
  message += "\nArguments: ";
  message += server.args();
  message += "\n";
  for (uint8_t i = 0; i < server.args(); i++) {
    message += " " + server.argName(i) + ": " + server.arg(i) + "\n";
  }
  server.send(404, "text/plain", message);
  digitalWrite(LED_BUILTIN, HIGH);
}


/* =======================================
 *              
 *                  SETUP
 * 
 * =======================================
 */
void setup(void) {

  // Reset the serial monitor at the beginning.
  Serial.flush();

  // Initial variables and setup
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH);
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  Serial.println("");

  /* Wait for the connection
   *
   * Connection status codes:
   *    0 : WL_IDLE_STATUS when Wi-Fi is in process of changing between statuses
   *    1 : WL_NO_SSID_AVAILin case configured SSID cannot be reached
   *    3 : WL_CONNECTED after successful connection is established
   *    4 : WL_CONNECT_FAILED if connection failed
   *    6 : WL_CONNECT_WRONG_PASSWORD if password is incorrect
   *    7 : WL_DISCONNECTED if module is not configured in station mode
   * Source: https://arduino-esp8266.readthedocs.io/en/latest/esp8266wifi/readme.html#diagnostics
   */
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
    Serial.print(WiFi.status());
  }
  Serial.println("");
  Serial.println("----------------------------");
  Serial.print("Connected to ");
  Serial.println(ssid);
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  if (MDNS.begin("esp8266")) {
    Serial.println("MDNS responder started");
  }

  server.on("/", handleRoot);

  server.on("/switch", handleLedSwitch);

  server.on("/status", handleLedStatus);

  server.on("/gif", []() {
    static const uint8_t gif[] PROGMEM = {
      0x47, 0x49, 0x46, 0x38, 0x37, 0x61, 0x10, 0x00, 0x10, 0x00, 0x80, 0x01,
      0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0x2c, 0x00, 0x00, 0x00, 0x00,
      0x10, 0x00, 0x10, 0x00, 0x00, 0x02, 0x19, 0x8c, 0x8f, 0xa9, 0xcb, 0x9d,
      0x00, 0x5f, 0x74, 0xb4, 0x56, 0xb0, 0xb0, 0xd2, 0xf2, 0x35, 0x1e, 0x4c,
      0x0c, 0x24, 0x5a, 0xe6, 0x89, 0xa6, 0x4d, 0x01, 0x00, 0x3b
    };
    char gif_colored[sizeof(gif)];
    memcpy_P(gif_colored, gif, sizeof(gif));
    // Set the background to a random set of colors
    gif_colored[16] = millis() % 256;
    gif_colored[17] = millis() % 256;
    gif_colored[18] = millis() % 256;
    server.send(200, "image/gif", gif_colored, sizeof(gif_colored));
  });

  server.onNotFound(handleNotFound);

  server.begin();
  Serial.println("HTTP server started");
  Serial.println("----------------------------");
}

void loop(void) {
  server.handleClient();
  MDNS.update();
}