CFL Analysis – Various Limitations

Unlike incandescent lamps which fit and work in practically any traditional indoor or outdoor luminaire (light fitting) and performs as well in the freezer or in the oven as in room temperature, CFLs come in so many varieties – each of which has its specific limitations, besides the widely varying quality and colour range – that it can be difficult to impossible for the average consumer to get the right CFL in the right luminaire without guidance from a professional expert in a lamp shop.

Stricter requirements for such information on the package may come soon but this still requires a more alert customer who knows in advance exactly for which luminaire the CFL is intended and who has the time to run around different stores to find just the right CFL for this application.

Grabbing just any CFL at the supermarket is a real gamble. Using a CFL in the wrong luminaire may cause them to give less light (and more heat), last only a fraction of the rated life, or malfunction immediately. Here are some examples:

• Unless specifically designed for such applications, temperatures over 50 degrees Celsius will also drastically reduce output and life rate in most CFLs. Many CFLs therefore cannot be used in closed luminaires or in downlights as they get overheated and soon fail. [1] Some leading manufacturers have created special reflector lamps for recessed downlights.

• Unless specifically designed for outdoor use, most CFLs light up very slowly – if at all – and don’t give much light in cold temperatures.

• Due to the slow start-up time (1-7 minutes in early life for some of the best bulbs according to consumer test [4]) CFLs with electronic ballasts are not recommended for use in bathrooms, closets and storage spaces as one may have already finished one’s business there by the time they reach full output, and many CFLs need to be left on for at least 15 minutes before switching off again.

Update Aug 2012: According to latest consumer tests (see Consumer Tests under Pages), leading brand CFLs do start quicker now, at least initially and at room temperature, but it still varies a lot between different models, lamps and brands, and none are instant.

• Some CFLs may still be sensitive to rapid on-off switching, especially cheaper ones, and only 70-75% of Energy Star rated CFLs passed the Rapid Cycle Stress Test. [2]

• Some CFLs may be sensitive to moisture and condensation.

• Using them with dimmers may kill both the lamp and the dimmer, [3] unless the CFL is specifically designed for dimmers – which makes them a lot more expensive, hard to find, and dimming may not use less electricity. All that happens when you dim a CFL is that it might start flickering or humming and the light will look extra unnatural at low light levels since it does not get warmer in colour but rather even more cold and grey. Whereas an incandescent light source dims beautifully due to the tungsten filament being a black-body radiator where colour naturally follows brightness along the Planck curve.

• Most CFLs don’t work with timers, sensors or ceiling fans.

• Some luminaires are too small to make even the smallest CFL fit.

• Many CFLs are meant to be used in base-up position in order to perform as stated. (In lab tests, CFLs are often tested in this position, so their performance is likely to appear much better than when used in most home luminaires.) CFLs with specific optimal burning position will not work well in luminaires designed for other burning positions. How many know of this, find this information on the package when they buy a CFL, or know what it means if the information is there?

• Bare tubes are more glaring than the CFLs with an extra outer bulb and should only be used in shaded luminaires which are open at the top and bottom.

• Risk of UV-radiation makes bare tubes unsuitable for desk- and reading luminaires, and around children and people with cataracts, lupus and other UV-light sensitivity conditions. [5, 6,]

This leaves very few luminaires and situations where a standard CFL will work as advertised. Possibly only in the garage or kitchen, where many already have pre-installed FL tubes, compact FL tubes without integrated ballasts or recessed low-voltage halogen which cannot be replaced by CFL.

Tips on where CFLs may be suitable: Using Lights at Home
Another good site for detailed CFL info: Compact Fluorescent Bulb Research

1. The CFL Myth
2. PEARL: Evaluation and Analysis of Residential Lighting
3. Should There Be a Ban on Incandescent Lamps?
4. GP Test: Lågenergilampor
5. Health Protection Agency
6. SCENIHR Report on Light Sensitivity


• Incandescent bulbs of common wattages can be bought in bulk and kept in reserve at home for when they’re needed, and will fit in practically any luminaire with the same size socket, and work just as well regardless of temperature etc, etc.

• Different CFL models each have their specific limitations & requirements and will only work well and last long within the temperature range, burning position, luminaire type and on-off switching which that particular model is designed for.

• Without professional guidance and knowing in advance which luminaire one intends the CFL for, it can be hard to impossible for customers to get the right CFL for a given luminaire (light fitting).