This is a WIP of my first serious Processing project. I am planning to use MIDI input later for activating the individual LEDs. All suggestions welcome! (Edit: updated code)

1. import java.util.Iterator;
2. 
   color[] pallete = {
3.   #E65350,
4.   #FAE400,
5.   #A6E800,
6.   #7C9CFF,
7. };
8. 
   
9. color defaultColor = #010101;
10. 
    
11. class LED {
12.   PVector position;
13.   int w;
14.   int h;
15.   color initialColor;
16.   color defaultColor = #010101; 
17.   color c;
18.   float amt = 0;
19. 
    
20.   LED(PVector _position, int _w, int _h) {
21.     position = _position;
22.     w = _w;
23.     h = _h;
24.     initialColor = pallete[int(random(pallete.length))];
25.     c = defaultColor;
26.   }
27.   
28.   void go() {
29.     update();
30.     display();
31.   }
32.   
33.   void pulse() {
34.     amt = 1.0;
35.   }
36.   
37.   void update() {
38.     if (amt > 0) {
39.       c = lerpColor(defaultColor, initialColor, amt);
40.       amt -= 0.01;
41.     }
42.   }
43.   
44.   boolean within(int x, int y) {
45.     return x >= position.x && y >= position.y &&
46.            x <= (position.x + w) && (y <= position.y + h);
47.   }
48.   
49.   void display() {
50.     fill(c);
51.     stroke(0);
52.     strokeWeight(2);
53.     rect(position.x, position.y, w, h);
54.   }
55. }
56. 
    
57. class LEDPanel {
58.   ArrayList<LED> leds;
59.   int rows = 10;
60.   int cols = 10;
61.   
62.   LEDPanel() {
63.     int w = width / rows;
64.     int h = height / cols;
65. 
    
66.     leds = new ArrayList<LED>();
67.     for (int i = 0; i < rows; i++) {
68.       for (int j = 0; j < cols; j++) {
69.         PVector position = new PVector(i * w, j * h);
70.         leds.add(new LED(position, w, h));
71.       }
72.     }
73.   }
74. 
    
75.   LED randomLED() {
76.     return leds.get(int(random(rows * cols)));
77.   }
78.   
79.   LED within(int x, int y) {
80.     for (LED led : leds) {
81.       if (led.within(x, y)) {
82.         return led;
83.       }
84.     }
85.     return null;
86.   }
87. 
    
88.   void go() {
89.     for (LED led : leds) {
90.       led.go();
91.     }
92.   }
93. }
94. 
    
95. LEDPanel panel;
96. 
    
97. void setup() {
98.   size(500, 500);
99.   background(255);
100.   panel = new LEDPanel();
101. }
102. 
     
103. int t = 0;
104. void draw() {
105.   if (t % 5 == 0) {
106.     panel.randomLED().pulse();
107.   }
108.   t += 1;
109.   panel.go();
110. }
111. 
     
112. void mouseMoved() {
113.   panel.within(mouseX, mouseY).pulse();
114. }