Arduino Mega LED doesn't light as expected
While it is true that your loop is incorrect, the coding error is unlikely to cause the behaviour that you have described.

Please ensure that a current limiting resistor is placed in series with each LED. Since you have 14 LEDs, you will need 14 current limiting resistors. 470 Ohm resistors (or similar) should be adequate for this purpose.

As per the other comments, C++ Arrays start at 0, not 1. The last element is the size of the array minus 1. In your case 14 - 1 = 13. Thus the loop can continue as long as the index is &lt; 14 (or &lt;= 13)

Thus your loops should read:

for(int r=0; r&lt;14; r++ ) {
  digitalWrite(LED[r],HIGH);
  delay(100);
}