What is the difference between a low energy simulated
daylight compact fluorescent lamp and the standard warm white bulb we have
been using for years? How do they save electricity? What do Lumens and
colour temperature mean? Without being too technical, I thought a brief
overview and clarification of the main terms used might be a helpful guide
to enlighten you.
For well over a hundred years, most of our
homes have been lit by incandescent bulbs. These standard light bulbs are
basically a thin wire filament connected to two feed wires, encased in a
sealed glass globe. The filament is brought to white heat by an electric
current passing through it. Being basically the same principle as an
electric fire, its little wonder that these bulbs get very hot. In fact
over 90% of the electricity used produces heat with less than 10%
producing light, a huge waste of energy and your money.
In today's society, our choice of lighting
involves many more considerations than ever before. The main two being the
environment and financial, which can be tackled together with one
solution.
Traditional incandescent bulbs produce
light through heat. This wastes huge amounts of energy and contributes to
high electricity bills. The desirable solution is for the electricity used
to provide light without producing a lot of heat which is wasted.
Fluorescent strip lights produce light more
efficiently and therefore more economically. These have been around for
many years and are ideal for shops, offices and maybe your kitchen but few
people would want them throughout their homes.
Over the past decade or so, the fluorescent
principle has been developed into bulbs which fit standard light fittings.
These are known as Compact Fluorescent Lamps (C.F.L). There are various
shapes and sizes but most people now choose the spiral shape as it is more
decorative and compact than the straight stick type. Basically it is a
narrow fluorescent tube, generally about 12mm diameter, formed into 3 or 4
loops.
Compact Fluorescent Lamps work much like
fluorescent strip lights. They consist of a glass tube coated with
phosphors and filled with a low pressure mix of gasses and an electronic
ballast to control the current to the electrodes, causing the gasses to
glow and excite the phosphors which emit the light.
So, whilst a 100 watt incandescent bulb
burns 100 watts of electricity, most of which is used to produce heat, a
compact fluorescent lamp will produce the same amount of light by using
about 20 watts of electricity. It is important to understand the
difference between power used and light produced. Watts are how much power
(ie electricity) you are using.
Light produced is measured in Lumens which
is an extension of the old foot-candle method of measuring the brightness
of a candle one foot away and a Lumen is equal to one foot-candle falling
on an area of one square foot. It follows therefore that the brightness of
any given source of light depends on the light emitted from the bulb and
how far away the measurement is taken. To say that a bulb is 1800 Lumens
is meaningless without qualifying the base unit and distance. The
generally accepted industry standard is to express the measurement per
watt, taken at 1 metre. Most CFL's are in the region of 60Lpw@1m, meaning
60 Lumens per watt at 1 metre. Some ads quote a Lumens rating which has
been taken at 50cm or even 25cm, which will be much higher.
The latest development in the technology of
CFL's is a daylight rated bulb. So what is the difference between warm /
soft / cool white and daylight? The colour of light is determined by its
wavelength, from the long wavelength red spectrum to the short wavelength
blue. The two ratings commonly used are colour temperature and colour
rendition index.
Colour temperature is expressed in Kelvins
and is based on the temperature a black metal body would need to be heated
to produce a given light. As CFL's do not heat a black body source (ie a
filament) the comparison is theoretical and referred to as Correlated
Colour Temperature (CCT). Visible light ranges from 1500k to 9000k,
representing a reddish hue -to- orange -to- yellow -to- white -to- blue.
Traditional warm white is 2700k (quite a yellow tint), cool white is 4200k
(slightly off-white) and daylight ranges from 5000k to 6500k, beyond which
starts to tint blue.
Colour rendering is a system that
mathematically compares how accurately eight specified pastel colours
appear under different light sources when compared with a standard source,
normally considered to be daylight. Put another way: if you are in a shop
looking at say a grey item of clothing, you may take it outside and find
that it is in fact beige. In theory, the maximum CRI is 100 but most
compact fluorescent daylight bulbs rate between 76 and 84. CRI does have
it limitations but as a general rule, the higher the CRI, the more
realistic colours will appear.
A brief word on 'Full Spectrum'. This is
not a technical term, it is a marketing expression, used to describe an
electric light source which emulates natural daylight. But daylight does
not have a fixed spectrum as it varies with position on earth, time of
year and day, colour of the sky (clear or cloudy?) and ground reflection
(city, field, ocean, snow?) and air polution.
There can't really be a blueprint for the
best type of lighting for each given room in any house because lifestyles
vary from home to home and people use rooms for a different combination of
activities. To provide the right type and amount of light for the
activities and atmosphere in each room will probably call for a
combination of different lamps.
In the interests of energy efficiency and
saving money for yourself, always try to use fluorescent tubes or compact
fluorescent bulbs for the lights you use most. Warm white (2700k) are the
cheapest and may suit general background lighting. Cool white (4200k)
where a clearer light is needed. Daylight (5000k to 6500k) where a really
clean light is needed.
