How do I make a lighter version of a colour using PHP?

This SO question has a full-blown PHP script that can convert a RGB to a HSL colour, and increase its H component of a HSL colour - it should be trivial to change to increase L instead.

In general if you want a lighter shade of a particular colour, the most accurate process is to convert from RGB to HSL (or HSV), change the 'L' (or 'V') value which represents lightness, and then convert back to RGB.

This will preserve the "hue", which represents where the colour sits on the spectrum, but change the "tint" (if lightening) or "shade" (if darkening) of that colour.

See http://en.wikipedia.org/wiki/HSL_and_HSV for more information.

On this website: http://www.sitepoint.com/forums/showthread.php?t=586223 they are talking about this code which is originally made by opensource Drupal. Seems to work fine in PHP!?

Now, how do I now indermingle myself with this code and change the lightness of an HSL value, before its outputted as RGB again?

<?php### RGB >> HSLfunction _color_rgb2hsl($rgb) {  $r = $rgb[0]; $g = $rgb[1]; $b = $rgb[2];  $min = min($r, min($g, $b)); $max = max($r, max($g, $b));  $delta = $max - $min; $l = ($min + $max) / 2; $s = 0;  if ($l > 0 && $l < 1) {    $s = $delta / ($l < 0.5 ? (2 * $l) : (2 - 2 * $l));  }  $h = 0;  if ($delta > 0) {    if ($max == $r && $max != $g) $h += ($g - $b) / $delta;    if ($max == $g && $max != $b) $h += (2 + ($b - $r) / $delta);    if ($max == $b && $max != $r) $h += (4 + ($r - $g) / $delta);    $h /= 6;  } return array($h, $s, $l);}### HSL >> RGBfunction _color_hsl2rgb($hsl) {  $h = $hsl[0]; $s = $hsl[1]; $l = $hsl[2];  $m2 = ($l <= 0.5) ? $l * ($s + 1) : $l + $s - $l*$s;  $m1 = $l * 2 - $m2;  return array(_color_hue2rgb($m1, $m2, $h + 0.33333),               _color_hue2rgb($m1, $m2, $h),               _color_hue2rgb($m1, $m2, $h - 0.33333));}### Helper function for _color_hsl2rgb().function _color_hue2rgb($m1, $m2, $h) {  $h = ($h < 0) ? $h + 1 : (($h > 1) ? $h - 1 : $h);  if ($h * 6 < 1) return $m1 + ($m2 - $m1) * $h * 6;  if ($h * 2 < 1) return $m2;  if ($h * 3 < 2) return $m1 + ($m2 - $m1) * (0.66666 - $h) * 6;  return $m1;}### Convert a hex color into an RGB triplet.function _color_unpack($hex, $normalize = false) {  if (strlen($hex) == 4) {    $hex = $hex[1] . $hex[1] . $hex[2] . $hex[2] . $hex[3] . $hex[3];  } $c = hexdec($hex);  for ($i = 16; $i >= 0; $i -= 8) {    $out[] = (($c >> $i) & 0xFF) / ($normalize ? 255 : 1);  } return $out;}### Convert an RGB triplet to a hex color.function _color_pack($rgb, $normalize = false) {  foreach ($rgb as $k => $v) {    $out |= (($v * ($normalize ? 255 : 1)) << (16 - $k * 8));  }return '#'. str_pad(dechex($out), 6, 0, STR_PAD_LEFT);}/* $testrgb = array(0.2,0.75,0.4); //RGB to start withprint_r($testrgb); */      print "Hex: ";  $testhex = "#b7b700";      print $testhex;  $testhex2rgb = _color_unpack($testhex,true);       print "<br />RGB: ";  var_dump($testhex2rgb);      print "<br />HSL color module: ";  $testrgb2hsl = _color_rgb2hsl($testhex2rgb); //Converteren naar HSL  var_dump($testrgb2hsl);      print "<br />RGB: ";  $testhsl2rgb = _color_hsl2rgb($testrgb2hsl); // En weer terug naar RGB      var_dump($testhsl2rgb);       print "<br />Hex: ";  $testrgb2hex = _color_pack($testhsl2rgb,true);  var_dump($testrgb2hex);?>