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.
Typical situations which will benefit from indoor simulated daylight include:
- S.A.D. Relief of Seasonal Affective Disorder
- Photography - Art - Crafts - Hobbies - Close Intricate work
- Where realistic colour definition is needed
Final tip: When some people start using daylight bulbs, they get the impression that the light is not bright enough. This is because the bulbs are not as fierce and dazzling as incandescent bulbs, also they can take up to 30 seconds to reach full glow.
To demonstrate the difference in the quality of the light, try this experiment. Turn on a daylight bulb and leave the room and go into a room with an incandescent light. After a couple of minutes, return to the room with the daylight bulbs and the difference will be very evident.
More information can be found in the booklet 'Indoor Daylight' written by Denis Knockton and available exclusively from UKRDESIGN