Finding the correct lighting solution for your retail store has become a complicated project. In addition to designing lighting to perform as required for the illumination of the various tasks within a store (general display, individual product display, transaction areas, general circulation, storage, etc.), designers must do this within energy code requirements. These codes impose a tough burden on both designers and lighting manufacturers but they have reduced typical retail lighting loads by at least 50% over the past couple of decades. Lighting designer, Warren Charter of Charter Sills has suggested that we use an automotive analogy to help find the efficiency of lighting fixtures as follows:

“The easiest way to understand Lumens per Watt (LPW) is the same way we look at Miles per Gallon (MPG). Similar to having a car that gets high MPG, say like a Prius, we want lamps that produce more light output, or lumens for the wattage they consume. Some high LPW lamps include the low wattage HID par, or compact fluorescent lamps. Lamps that are similar to the Hummer, that have a lower LPW include some of the older incandescent like the A-lamps, and most R-lamps. In short, the higher the LPW the more efficient the lamp is as it relates to light output. Technically speaking, the formula for LPW is the same as MPG. Simply take the total number of lumens for the lamp, and divide by the wattage for the lamp to determine the LPW. Example, 900 Lumens divided by 60 Watts gives you an LPW of 15.” 

Generically, incandescent lamps have an LPW of about 18 and LED, Metal halide, and Fluorescent have LPW’s that range from 30 to 110. So why not just pick the most efficient lamps and run with them. Well just like automobiles every lamp has different characteristics. A car that gives you great mileage may be underpowered for autobahn-type use, or it may lack the agility to negotiate a mountain road, or it may be incapable of being driven off-road. It all depends where and how you want to drive. Similarly with your choice of lamp and fixture types, it all depends on what you want the lamp to accomplish. Some jobs, like individual product display, may require using lamps that less efficient but more focused. Other tasks like providing for general circulation within a store can be accomplished with high LPW lamps. Within the current lighting and energy codes, the designer has a fixed total of watts available for use. The trick is to balance the type and number of lamps and fixtures available to achieve proper lighting while maintaining an energy focus.