Velleman Compact fluorescentlamps(CFL) - Manual (Page 4)

Size
CFL light output is roughly proportional to phosphor surface area and high output CFLs are
often larger than their incandescent equivalents. This means that the CFL may not fit well in
existing light fixtures.
Dimming
Only some CF lamps are labelled for dimming control. Using regular CFLs with a dimmer is
ineffective at dimming, can shorten bulb life and will void the warranty of certain
manufacturers. However, dimmable CFLs are available. The dimming range of CFLs is usually
between 20% and 90%. Dimmable CFLs are not a 100% replacement for incandescent fixtures
that are dimmed for "mood scenes" such as wall sconces in a dining area. Below the 20%
limit, the lamp remains at the approximate 20% level, in other cases it may flicker or the
starter circuitry may stop and restart. Above the 80% dim limit, the bulb will generally glow
at 100% brightness. Dimmable CFLs have a higher purchase cost than standard CFLs due to
the additional circuitry required for dimming. A further limitation is that multiple dimmable
CFLs on the same dimmer switch may not appear to be at the same brightness level.
Perceived Coldness of Low Intensity CFL
When a CFL is dimmed the colour temperature (warmth) stays the same. This is different
from most other light sources (such as the sun or incandescent lamps) where colour gets
warmer as the light source gets dimmer. Emotional Response Testing suggests that people
find dim, bluish light sources to be cold or even sinister. This may explain the persistent lack
of popularity for CFLs in bedrooms and other settings where a subdued light source is
preferred.
Time to achieve full brightness
Compact fluorescent lamps may provide as little as 50–80% of their rated light output at
initial switch on and can take up to three minutes to warm up, and colour cast may be
slightly different immediately after being turned on. This compares to around 0.1 seconds for
incandescent lamps. In practice, this varies between brands/types. It is more of a problem
with older lamps, 'warm (colour) tone' lamps and at low ambient temperatures.
Outdoor use
CFLs that are not designed for outdoor use will not start in cold weather. CFLs are available
with cold‐weather ballasts, which may be rated to as low as ‐23°C . Standard compact
fluorescents will fail to operate at low temperatures. Light output drops at low temperatures.