Re: Compact Fluorescent Light Bulbs – A Tale From Dust to Dust

The heating effects that you mentioned are important, and need to be considered. In a simplistic analysis there are two basic scenarios to consider: heated rooms and cooled rooms:

Scenario 1: Heated rooms

If the bulb is used in a room that normally requires heating then all types of bulb, operate with 100% energy efficiency, because all of the input energy is converted to required heat. If the heating from bulbs is reduced by switching to CFLs then the primary heating system will simply make-up the difference in order to reach the thermostat temperature.

Consequently, in the best case where the heating is derived from in-the-room electric heaters, the overall operational energy saved by switching from incandescent lamps to CFLs, is zero; no energy is saved (the bulbs contribute less heat so the heater contributes more, to make-up the shortfall). However, if the heating system is of a type (such as a gas boiler) that vents large amounts of heat to the outside then the use of CFLs will lead to reduction in overall energy efficiency because the boiler will work more, causing greater amounts of heat to be wastefully vented.

Rooms that require heating should not, therefore, be illuminated with CFLs since no energy will be saved.

Scenario 2: Cooled rooms

If the bulb is used in rooms that normally require cooling then the heat generated by the lighting gives the cooling system more work to do. Reducing the energy used by lights reduces the total heat into the room and thus reduces the need for cooling.

In cooled rooms, therefore, swapping a 100W incandescent lamp for a 20W CFLs leads to an energy saving greater than 80W/h because the cooling system will also require less input energy. The exact amount saved depends how much energy is used (in KW/h) by the cooler to move 80W/h out of the room.

Even here, however, it is important to pay attention to the times when lamps and cooling are used. The greatest need for cooling is generally when the sun is brightest and the need for lamps lowest. At the times when the room is so bright that lamps are not switched on then it doesn't matter what kind of lamp is in the lampholder.

The aforegoing analysis is very simplistic, and most real world scenarios will be much more complex. Most rooms are not permanently heated or cooled, some are heated and cooled at different times. Many lamps are used in spaces that require neither heating or cooling. To evaluate any real-world scenario it would be necessary to know the duty cycles of the lights and heaters and coolers, and the overlap in operation. It would also be necessary to understand the feedback mechanism for the heater or cooler (i.e. understand the operational parameters for the thermostat). Another hard-to quantify factor would be human perception of temperature and comfort; are many small distributed heaters (aka lamps) perceived to create a more comfortable space than one centralized heater?

Nonetheless, despite the simplicity, I hope the above is sufficient to show that purely in terms of operational energy (i.e. ignoring embodied energy and disposal energy) the use of CFLs is not guaranteed to reduce energy use. My own view is that anybody who lives in a place where lighting and heating are often required together (e.g. places such as Canada, the northern states of the USA, northern Europe, northern Asia) should not use CFLs. People who live in places that tend to be bright possibly don't use enough lighting for it to be worth worrying about. People who living places that are well lit but often uncomfortably warm can reduce the temperature by switching to CFLs. Maximum potential energy-saving benefits are likely to be had in places that simultaneously require lighting and cooling.