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<h1>LED savings calculator</h1>
//electricity_cost inc_watts led_watts led_cost bulbcount hoursday, compute savings_year and payback_in_years
function validateForm(form) {
if ( form.electricity_cost.value == "" || parseFloat(form.electricity_cost.value)<=0.0) { alert("Please enter the cost of your electricity."); return false; }
if ( form.inc_watts.value=="" || parseInt(form.inc_watts.value)<=0) {alert("Please enter the wattage of the incandescent bulb."); return false; }
if ( form.led_watts.value=="" || parseInt(form.led_watts.value)<=0) {alert("Please enter the wattage of the LED bulb."); return false; }
if ( form.inc_life.value=="" || parseInt(form.inc_life.value)<=0) {alert("Please enter the expected life in hours of the incandescent bulb."); return false; }
if ( form.led_life.value=="" || parseInt(form.led_life.value)<=0) {alert("Please enter the expected life in hours of the LED bulb."); return false; }
if ( form.inc_cost.value=="" || parseFloat(form.inc_cost.value)<0) {alert("Please enter the cost of a replacement incandescent bulb."); return false; }
if ( form.led_cost.value=="" || parseFloat(form.led_cost.value)<0) {alert("Please enter the cost of the LED bulb."); return false; }
if ( form.bulbcount.value=="" || parseInt(form.bulbcount.value)<=0) {alert("Please enter the number of bulbs being replaced."); return false; }
if ( form.hoursday.value=="" || parseFloat(form.hoursday.value)<=0) {alert("Please enter the hours per day the bulb is typically on."); return false; }
return true;
function roundPennies(s) {
var str=s.toString()+"0000";
var indexdot = str.indexOf(".");
var len=str.length;
if (indexdot>0 && indexdot<str.length+3) {
return s;
function Calculate(form) {
savings_year = "0.00";
payback_in_years = "99.99";
if ( result ) {


// What's the LED energy cost per hour?
led_cost_per_hour = led_watts * electricity_cost / 1000;
inc_cost_per_hour = inc_watts * electricity_cost / 1000;

// What's the replacement cost per hour of use?
led_opcost_per_hour = led_cost / led_life;
inc_opcost_per_hour = inc_cost / inc_life;

// Total operating cost per hour
led_cost_per_hour = led_cost_per_hour + led_opcost_per_hour;
inc_cost_per_hour = inc_cost_per_hour + inc_opcost_per_hour;

// Total cost per year
led_cost_year = hours_year * led_cost_per_hour;
inc_cost_year = hours_year * inc_cost_per_hour;

// Savings per year and delta cost on purchase price
savings_year = inc_cost_year - led_cost_year;
delta_cost = led_cost - inc_cost;

// Payback period
payback_period = delta_cost / savings_year;

// Savings / year should be multiplied by bulb count - but this
// should not affect payback period.
savings_year *= bulb_count;
form.savings_year.value = savings_year;
form.payback_in_years.value = payback_in_years;

// end of code hiding -->



<p>Use this LED savings calculator to figure out how much money you can save by installing <a href="http://www.green-energy-efficient-homes.com/led-house-lights.html">LED house lights</A> to replace incandescent lights.</p>
<p>The calculator assumes an average incandescent bulb lifetime of 1,000 hours and an average LED house light lifetime of 50,000 hours.
You can change this if you wish based on the advertised lifetime hours of either the original or replacement bulb, or both.</p>
<p>For compact fluorescent (CFL) lights, see my <a href="http://www.green-energy-efficient-homes.com/cfl-savings-calculator.html">CFL savings calculator.</a></p>
<FORM NAME="LED_savings">
<table border="0">
<tr><td align="right">Your electricity cost, in $/kwh</td><td><INPUT TYPE=text NAME=electricity_cost VALUE="0.10" SIZE=15></TD></tr>
<tr><td align="right">Wattage of incandescent bulb being replaced</td><td><input type=text name=inc_watts value="100" size=15></td></tr>
<tr><td align="right">Wattage of LED to replace the incandescent</td><td><input type=text name=led_watts value="13" size=15></td></tr>
<tr><td align="right">Cost per incandescent bulb (for when bulb burns out)</td><td><input type=text name=inc_cost value="0.49" size=15></td></tr>
<tr><td align="right">Cost per LED replacement bulb</td><td><input type=text name=led_cost value="19.00" size=15></td></tr>
<tr><td align="right">Incandescent bulb life (hours)</td><td><input type=text name=inc_life value="1000" size=15></td></tr>
<tr><td align="right">LED bulb life (hours)</td><td><input type=text name=led_life value="50000" size=15></td></tr>
<tr><td align="right">Number of bulbs of this type being replaced</td><td><input type=text name=bulbcount value="1" size=15></td></tr>
<tr><td align="right">Number of hours/day light is in use</td><td><input type=text name=hoursday value="2" size="15"></td></tr>
<tr><td colspan="2" align="right"><INPUT TYPE="button" VALUE="Calculate savings" onClick="Calculate(this.form)"></tr></td>
<tr><td align="right">Savings per year</td><td><input type=text name=savings_year size=15></td></tr>
<tr><td align="right">Payback in years</td><td><input type=text name=payback_in_years size=15></td></tr>