Incandescent Downlighting To Compact Fluorescent Lamps

Most downlighting fixtures installed in residential and commercial facilities are equipped with incandescent lamps. In many cases, significant energy savings can be achieved by replacing these lamps with compact fluorescent lamps. Compact fluorescent lamps can deliver comparable light output for about one fourth the wattage. This table shows a comparison of incandescent lamps and compact fluorescent lamps.

One thing to consider, when retrofitting incandescent fixtures with compact fluorescent lamps, is that the illuminance at the workplane will usually be less for compact fluorescent lamps than it is for incandescent lamps. This holds true even if both lamps deliver the same lumen output. This occurs because incandescent lamps focus more light out of the fixture. Much of the fluorescent light from compacts gets trapped in the fixture. Therefore, it usually makes good sense to use compact fluorescent lamps of one half the wattage of incandescent rather than the one fourth replacement.

In addition to dramatic energy savings, compact fluorescent lamps also burn much cooler thus reducing the load on the cooling system.

Cost Savings

1. The first step in calculating the energy savings for this retrofit is to determine the demand savings. You can look up system wattages in the previous chart. The demand saved is equal to the wattage reduction (the difference between the wattage of the current system and the wattage for the system with electronic ballast)...multiplied by the number of fixtures in the space. Remember to convert watts to kilowatts by simply dividing the total watts saved by 1,000.
   
   Demand Savings = Old Wattage - New Wattage / 1000 * Number of Fixtures

2. Next, calculate the energy saved by this retrofit. This is simply the total demand saved in kilowatts times the total annual operating hours. This will give you the total kilowatt-hours saved per year.
   
   Energy Savings = Demand Savings * Annual Operating Hours

3. The next step is to calculate the actual cost savings associated with these demand and energy savings. Demand cost savings is simply the demand savings...times the demand charge ($10 in our example)...times 12 months (since demand is charge on a monthly basis.)
   
   Demand Cost Savings = Demand kW Savings * $/kW Demand Cost * 12 Months

4. Energy cost savings will simply be the annual kilowatt-hour savings times the cost per kilowatt-hour (which is 5 cents in our example).
   
   Energy Cost Savings = kWh Savings * $/kWh Energy Cost

5. The total annual savings is the sum of the demand cost savings and the energy cost savings.
   
   Total Annual Savings = Demand Cost Savings + Energy Cost Savings

The cost for installing this type of retrofit will vary. Equipment and labor costs for installation should both be considered. Once you know these costs you may evaluate the attractiveness of the project using any of the normal financial measures. Simple payback is probably the most common. This type of analysis will apply to most situations. Your operating hours and energy costs may be different but the calculations used in this example will still apply.

Advantages
Compact fluorescent lamps are much more efficient than incandescent lamps and they burn much cooler. This results in tremendous energy savings and a quick payback. In addition, compact fluorescent lamps last up to 10 times longer than incandescent lamps. Therefore, maintenance costs are also reduced. Further, since compacts are available in a 2700 degrees Kelvin color temperature, their appearance is much the same as incandescent lamps. Most people won't be able to tell the difference without actually looking into the fixture.

Disadvantages
In some cases building owners have complained that compact fluorescent lamps do not produce enough light for a downlighting fixture. This usually occurs when the compact fluorescent lamp does not have sufficient wattage to produce adequate light. In general, choose a compact fluorescent lamps that is approximately one half the wattage of the original incandescent lamp. If downlights are located in a very high ceiling you may want to consider retrofitting with a metal halide or high pressure sodium lamp. These lamps will usually work much better at delivering light to the workplane.

Another item to consider it changing out the fixtures to fixtures that are specifically designed for compact fluorescent lamps. These fixtures will deliver the maximum amount of light output for the source because their design takes the design of the compact fluorescent lamp into account.