DioLight Technology Inc. has its detractors in the light-bulb business; in fact, they far outnumber its fans. "Is it gimmickry? I don't know," says Don Thomas, manager of commercial engineering for GTE Lighting Products. Thomas complains, with cause, that DioLight stresses the longer life of its bulbs without drawing attention to the trade-offs in reduced light or higher energy costs. "It confuses the unsophisticated buyer," he charges.

Trade-offs there are; in light bulbs, as in life, there is no free lunch. If you want a bulb that lasts longer, you'll pay for it, either with higher energy costs or with less light per watt. So whether long-life bulbs are a good deal or not depends on who is using them and how.

Figure it this way: the cost of light includes bulb cost, energy cost, and the cost of changing a bulb when it burns out. To compare a 60,000-hour, 60-watt DioLight bulb costing $4.99 with a standard 1,000-hour, 60-watt bulb costing 75?, you have to estimate the cost of changing a bulb. If that's significant, the DioLight bulb is usually the better buy, since the standard light bulb would have to be changed 60 times before the DioLight bulb burned out.

The catch, however, is that the DioLight bulb produces just 56% of the standard bulb's brightness -- 500 lumens versus 890 lumens. If you want almost the same light as from a standard 60-watt bulb, you'll have to use DioLight's 90-watt bulb. That would use up correspondingly more electricity, thus narrowing the cost gap considerably. And if you're using the bulb at home or in a situation where the labor cost of replacement is effectively zero, you can find yourself spending money just to avoid changing a light bulb now and then.