Traditionally, when purchasing a light bulb, one would usually only consider the wattage of the lamp, not what the lamp is going to be used for or how much light we want it to produce.

The higher wattage lamp one bought, it was assumed, the more light it would produce. The situation has changed. Now we have Choices. We can purchase strange-looking lamps with low wattage, but the package says they will produce as much light as a 60 or 100 watt light bulb. How is this possible?

With the wide range of different types of lamp now available, just knowing how many watts a lamp uses doesn't tell us anything about how much light it produces. We need to become comfortable using a few more terms.

The efficiency of lighting sources is rated in "efficacy" or Lumen(s) per watt. The watt is the time rate flow of radiant energy. The lumen is the time rate flow of luminous energy. A lamp receives watts and emits lumen(s). Light is made up of many different wave lengths - consider the rainbow that breaks up white light into it visual sources. If the light source could be concentrated at one wave length, one watt of radiant power, the energy supplied to the light bulb would yield one watt of lighting power or nearly 200 lumen(s). The traditional incandescent lamp emits much of its radiation in the infrared (heat producing) range of the lighting spectrum.

Incandescent lamps produce about 15 lumens per watt. A compact fluorescent yields about 70 lumens per watt, A 4 foot fluorescent lamp achieves 80 lumens per watt, And some types of street light produce 100 or more lumens per watt. The efficiency of the traditional lamp is about 10% based on its Wattage input. What happened to the rest of the energy? It is lost in heat produced. If we were to consider the whole system, all the way back to the generation plant producing the electricity we feed the lamp, the efficiency picture is even more grim. The generation plant itself is about 33% efficient.

If we don't happen to need the waste heat being given off by an incandescent lamp were using, the efficiency of the whole is roughly 3% from original source to useful light produced.

Any time you can substitute a more efficient light source for an incandescent bulb - DO it!