$light = 10 ;//10

$light_1 = ($light/2); //5
$light = $light/2;  //5
$light_2 = $light;//5

$light_top_1 = ($light_1/2);//2.5
$light_1 = $light_1/2;//2.5
$light_top_2 = $light_1;//2.5

$light_down_1 = ($light_2/2);//2.5
$light_2 = light_2/2;//2.5
$light_down_2 = $light_2;//2.5



for ($i = 0; $i<10 ; $i++)
{
echo "track".$i."<br />";

$light_end_top = $light_top_1 + $light_top_2;
echo "<br>"."light top = ".$light_end_top."<br>";

if ($i > 4 ) { $light_end_down = $light_down_1; }
else { $light_end_down = $light_down_1 + $light_down_2;}


echo "<br>"."light down = ".$light_end_down."<br>";


}