Efficient Lighting Blog

A lighting retrofit is the practice of replacing components in the system with counterparts that make it use energy more efficiently. A lighting upgrade is any strategy that reduces the system’s energy use. Energy savings are realized over time that can be significant enough to not only pay for the new equipment, but produce a return on the investment.

While manufacturers and professional lighting managers have computer software that calculate the economic benefits of an upgrade, it pays to understand the principles.

Understanding Energy Consumption

Utilities bill their customers in a variety of ways, including an energy use charge, demand charge, power factor charge, fuel adjustment charge and other charges. In this section, we will focus on reducing energy consumption.

Energy Consumption (kWh) = Input Watts (kW) x Time (hours operated in a given year)

To reduce energy consumption, therefore, we can either reduce the input wattage or reduce the hours of operation. Input wattage can be reduced by replacing lamps and ballasts with more-energy-efficient counterparts or outright removal of lamps and ballasts. The hours of operation can be reduced using sophisticated controls and other methods.

Example

Let’s look at two purely fictitious lighting systems, A and B. Lighting System A is the existing system and Lighting System B is a proposed retrofit system which simply includes more-energy-efficient lamps and ballasts. They produce comparable light output.

So we save $22.50 per year by replacing the lamps and ballasts in this fixture. For the 100 fixtures, we save $2,250 per year. Note that additional energy savings can be calculated from the air conditioning system, which now works less hard because less heat is produced by the lighting system (see Lighting and HVAC Interactions for more information).

Note that we simply could have installed occupancy sensors or some other controls that would reduce the hours of operation, or both strategies. If we installed new controls in this case and reduced the operating hours from 3,000/year to 2,300/year, we would produce an additional $700.00 in energy savings, or a total of $2,950 per year.

Payback and Return on Investment

Now that we know how much money we’re going to save while still enjoying comparable performance from the lighting system, it is time to do an economic analysis, which includes determining payback and return on investment (ROI). A full-fledged net present value analysis or life-cycle cost analysis is a major undertaking (best to use software), so for our purposes we will determine simple payback and ROI.

Simple payback is the amount of time in decimal years that will go by before a system upgrade option’s energy savings reach the net installation cost (also called the initial cost):

Payback (Years) = Net Installation Cost ($) ÷ Annual Energy Savings ($)

5-Year Cash Flow ($) = 5 Years - Payback (Years) x Annual Energy Savings ($)

Five-year cash flow was chosen based on expectations of the life of the lamps; by factoring in the cost of lamp replacement and other maintenance costs, a 10- or 20-year cash flow can be produced.

Simple return on investment is an internal rate of return, expressed as a percentage, based on the relationship between annual energy savings and the net installation cost:

ROI (%) = [Annual Energy Savings ($) ÷ Net Installation Cost ($)] x 100

Together, they represent a simple and effective first step at determining whether the new equipment would be a good investment for its owner.

In our example, let us suppose that the initial cost of the system (lamps/ballasts only) - - including the cost of the components and labor, waste disposal - - is about $70.00/fixture or $7,000 total (other initial costs may include financing, consulting fees, tax effects and waste disposal).

Simple payback is:

$7,000 ÷ $2,250 = 3.1 Years

Five-year cash flow is:

5 Years - 3.1 x $2,250 = $4,275

ROI is:

($2,250 ÷ $7,000) x 100 = 32%

These results usually must then be compared to the owner’s financial policies regarding capital investment to see if the ROI meets the internal “hurdle rate” and therefore enjoy the best chance of a green light by senior management. It is often desirable to examine a number of upgrade options to make the best choice. Note that some utilities offer programs that reward lower energy consumption with a dollar rebate that can make the upgrade even more attractive; also note that an energy service company may finance the upgrade.

Source: Lightsearch.com 

There are two systems of measurement commonly used to describe the color properties of a light source: “color temperature,” which expresses the color appearance of the light itself, and “color rendering index” (CRI), which suggests how an object illuminated by that light will appear in relation to its appearance under other common light sources. Both can be extremely valuable in evaluating and specifying light sources, but it is important to understand their limitations.

 Color Temperature–the Appearance of Light The color temperature of a light source is a numerical measurement of its color appearance. It is based on the principle that any object will emit light if it is heated to a high enough temperature, and that the color of that light will shift in a predictable manner as the temperature is increased. The system is based on the color changes of a theoretical “blackbody radiator” as it is heated from a cold black to a white hot state. With increased temperature, the blackbody would shift gradually from red to orange to yellow to white and, finally, to blue white. A light source’s color temperature, then, is the temperature, measured in degrees kelvin, expressed in kelvin (K), at which the color of the blackbody would exactly match the color of the light source.

For many light sources an exact match cannot be achieved. In such cases, the closest possible match is made, and the color is described as correlated color temperature. An OCTRON® T8 fluorescent lamp with a color temperature rating of 4100K, for example, has a color appearance similar to that of a blackbody heated to 4,100 kelvin (3827°Celsius, 6920° Fahrenheit). Warm vs. Cool–the Psychology of Light Some people find it confusing that low color temperature light sources are called “warm” while those with higher temperatures are referred to as “cool.” In fact, these descriptions have nothing to do with the temperature of the blackbody radiator but refer to the way color groups are perceived—the psychological impact of lighting. Colors and light sources from the blue end of the spectrum are referred to as cool, and those toward the red/ orange/yellow side of the spectrum are described as warm. How Light Affects the Colors of Objects Color rendering index (CRI) is a system derived from visual experiments. It assesses the impact of different light sources on the perceived color of objects and surfaces. The first step is to determine the color temperature of the light source being rated. Next, each of eight standard color samples is illuminated—first by the light source and then by a light from a blackbody matched to the same color temperature. If none of the samples changes in color appearance, the light source is given a CRI rating of 100. Any changes in color appearance which do occur result in a lower rating. The CRI decreases as the average change in the color appearance of the eight samples increases. Any CRI rating of 80 or above is normally considered high and indicates that the source has good color properties. Color Temperature and CRI–Useful References Color temperature and CRI provide some helpful information, but they are not perfect. Color temperature, for instance, fails to indicate anything about how a given light source will render colors. For example, imagine two “cool” light sources with similar color temperatures and color appearances. Suppose light source A produces fairly uniform energy, Suppose light source B, which looks the same, produces a similar spectrum except with almost no light in the red. Red objects which appear natural under light source A will therefore look dull and colorless under light source B even though both lights have the same color temperature. In general, a high CRI figure means a light source will render colors well. However, since CRI figures are calculated for light sources of a specific color temperature, it is not valid to compare a 2700K, 82 CRI light source to one of 3500K, 85 CRI. In addition, remember that CRI is an average of eight different colors. This means that a light source with a high CRI will tend to render the broad range of colors well, but it is not a guarantee that any specific color will appear natural. Used in conjunction, however, color temperature and CRI can provide excellent benchmarks for the comparison of light sources.