With inefficient incandescent bulbs being phased out by law, homeowners are now faced with the task of replacing ones that burn out. Even if you are already using some reduced-power CFL bulbs, replacing a burned-out incandescent bulb gives you an opportunity to see what other types of lighting are available for your particular application.
To choose a replacement bulb, first consider its use, since not all energy-saving bulbs are suitable for all uses. For example, a light bulb that might work well in a recessed overhead fixture might not work well in a table lamp.
How is energy efficiency measured?
Power consumed by a bulb is measured in watts, while light produced is measured in lumens. For energy efficiency you want a bulb that produces the highest number of lumens per watt – called efficacy – provided that the bulb meets your needs in terms of brightness, light spread, light color, heat dissipation, convenience, and general comfort.
Lights have different power and brightness ratings. In addition, in your home actual power consumed and resulting brightness will vary with your line voltage, which may be closer to 115V than to the 120V used in the ratings, so lightbulbs will be less bright.
To enable you to compare an energy-saving light with an incandescent, here is a list of typical efficacies of standard incandescents by wattage for reference (efficacy = lumens per watt):
Watts Lumens Efficacy
150 2680 18
100 1600 16
75 1125 15
60 800 13
40 470 12
What you should look for in a replacement bulb is not just lower power consumption in watts, but higher efficacy for the brightness you need. After all, you could replace all your 100-watt incandescents with 40-watt incandescents and save 60% on your electricity bill. But you need a certain amount of brightness – a number of lumens – for your application. So, for example, if you need 1600 lumens of light to read by, you will want to find a 1600-lumen replacement bulb that uses less than 100 watts of power – a bulb that has an efficacy higher than 1600/100, or 16.
Higher efficacy is the goal of consumers and bulb manufacturers alike.
What types of bulbs save energy over incandescents?
- A typical 12-watt LED light bulb might produce 800 lumens for an efficacy of 67, but some luminaires have been measured at 10-30% less due to inefficiencies in heat dissipation and lens quality, resulting in efficacy of 47-60.
- A typical 24-watt CFL might produce 1600 lumens, but with its ballast and power management it may use 10% more than its rated power, for efficacy of 61, declining to 43-48 as the bulb loses brightness over time.
- A typical 70-watt halogen luminaire might produce 1600 lumens for an efficacy of 23. It does not contain a ballast.
- A typical 100-watt incandescent produces 1600 lumens for an efficacy of 16 (our reference bulb). It does not contain a ballast.
So you replace your burned-out 100-watt incandescents with 24-watt CFLs or 12-watt LEDs, right? Perhaps. But you need more information. Here are some considerations beyond efficacy:
- Not all consumers like the light produced by CFLs, and they contain mercury, which can contaminate clothing and carpeting if the bulb breaks. Some CFLs have been found to produce high levels of UV light when tested. Some users complain of skin rashes and migraine. (UV-filtered CFLs and electronically-ballasted CFLs that eliminate flickering are available.)
- A 24-watt CFL will cost about $2.50 and may last for 8000 hours if mounted right side up in a well-ventilated location and lit for 4 hours per day. Most CFL’s do not work well upside down, in enclosed spaces, or with dimmers, reducing their useful life considerably. They take a few minutes to reach full brightness and even longer to warm up fully. Turning them on and off frequently during the day and turning them off before they are fully warmed up will shorten their life. About.com reported that turning a CFL off after one hour will reduce its life by 20-50% and cycling a CFL like an incandescent — for 5 to 30 minutes at a time — will reduce its useful life by 70-85%. So an 8000-hour-rated CFL would last, on average, for around 1800 hours. In fact, some users complain that CFLs do not last any longer than incandescents.
- A LED bulb is directional and has a light-spread of around 140 degrees compared to the 360 degrees of an incandescent, so it may not be satisfactory in a table lamp. But LED light bulbs are great in open recessed and track light fixtures, though not all LEDs work with dimmers.
- LEDs don’t work very well in enclosed spaces. Efficacy of some enclosed LED luminaires has been measured at 25-30.
- A 12-watt LED bulb will cost around $40 and last for 50,000 hours if used in a well-ventilated location.
- Instead of replacing a 1600-lumen incandescent bulb with an 800-lumen 12-watt LED bulb, why not use a 24-watt LED bulb that produces 1600 lumens for the same nominal efficacy of 67? Answer: Because it doesn’t exist commercially yet. In high-power applications LED bulbs produce too much heat; they would need to be cooled with an internal fan, which would eat up much of the power saving. And the initial cost might be higher than $40 too. So you can try the 800-lumen LED bulb. It might be a satisfactory replacement for the incandescent as a downlight.
Energy savings is one of several considerations
Two conclusions are apparent from our research:
- Efficacy and useful life of CFL and LED bulbs in practice are not as high as found in manufacturers’ testing and labeling.
- Efficacy (energy savings) is just one consideration in deciding what replacement bulb to buy. There are costs and tradeoffs and suitability issues that you need to take into account.
It might well be that for your particular need a 50-watt or 70-watt halogen bulb with an efficacy of 23, a cost of $6, and a useful life of 3000 hours is the most energy-efficient bulb you can buy right now. You might prefer such a bulb simply because it contains no mercury and warms up almost immediately, and you might attach a greater weight to those considerations than to the potential energy savings.
An important cost issue is the expected life of the bulb, measured in hours. The number of hours printed on a bulb package as its rated life – say 3000 hours – is not a guarantee of how long the bulbs in that package will last, but more like an expectation. It represents the median life of a large quantity of bulbs of that type based on testing in ideal conditions. For incandescent bulbs, it’s the expected time before the bulb burns out. For CFLs and LEDs, it’s the expected time before the bulb has lost 30% of its brightness (in lumens) or otherwise fails when lit for 4 hours per day.
What is median life? If you were to take a large number of identical incandescent bulbs – say 1000 – and measure how many hours each one lasted till it burned out, 500 of them will have burned out within 3000 hours (125 days of continuous use). The first bulb to burn out might actually have lasted only an hour, while the last one to burn out might last for a year or more.
You might be willing to pay more for a bulb with a longer useful life if it’s used in a place that’s hard to reach. But because the rated hours are just an expectation of its useful life, a particular bulb might not last nearly as long.
So, what are the best light bulbs to replace incandescents and save power? It all depends. Choosing a suitable green lighting replacemnt bulb is more than looking at watts or even efficacy for some uses. For replacement bulbs for lamps and ceiling fixtures, see our review of Philips halogen light bulbs.