Facts and figures

Choose an A-rated bulb because it:

• provides 4 times as much light per watt
• lasts up to 15 times longer than an incandescent bulb

To qualify for the recommended list, A-rated energy saving bulbs must fulfil the Trust’s requirements:

• A lifetime of at least 6,000 hours
• Must be capable of being switched on at least 6,000 times (at least the same number of times as the stated lifetime in hours)
• Must have good colour rendering (CRI or Ra index) of 80 minimum.

The quality requirements are based on the European CFLs Quality Charter for energy saving bulbs.

LIFETIME OF A-RATED ENERGY SAVING BULBS

A-rated bulbs last up to 15,000 hours
The life of an A-rated energy saving bulb is between 6,000 and 15,000 hours. Compare this with a conventional bulb; these have a typical life cycle of around 1,000 hours, the equivalent of around 1 year. You can see the lifetime of different bulbs on the Trust’s overview of recommended A-rated bulbs.

A-rated energy saving bulbs must be capable of being switched on and off many times
A recommended A-rated energy saving bulb must be capable of being switched on and off as many times as the life of the bulb in hours. For example, an A-rated bulb with a life of 10,000 hours must therefore be capable of being switched on at least 10,000 times.

 Colour rendering

A-rated bulbs have slightly poorer colour reproduction
Normally, most of us will not be able to register any colour difference when we compare the light from an incandesent bulb with the light from an A-rated energy saving bulb. But there is a difference. The ability of an A-rated bulb to reproduce certain colours is actually slightly poorer than a conventional bulb.

Choose an incandescent or halogen bulb for places where judging colours is important. In homes this can apply, for example, to lights over the dining table, above the bathroom mirror, or to lighting used in connection with particular hobby activities.

Colour quality
A bulb’s ability to reproduce colour is based on the CRI (colour rendering index) scale of 0-100, where the capacity of daylight to reproduce colour is rated at 100. An incandescent bulb’s colour rendering ability, which is 99, is very close to daylight. An ordinary A-rated bulb's CRI value is 80-85. You can see the CRI value for individual A-rated bulbs on the Trust’s overview of recommended A-rated bulbs.

Tri-phosphor and 5-phosphor energy saving bulbs
Energy saving bulbs (CFLs) are available with tri-phosphor and 5-phosphor coatings. Tri-phosphor CFLs have 3 primary colours, but 5-phosphor bulbs have more. This makes 5-phosphor CFLs somewhat better in colour terms, and therefore these typically have a CRI value of 90-95. Conversely, they are a little less energy efficient, namely 3 times more energy efficient than incandescent bulbs. Tri-phosphor CFLs are 4-5 times more efficient than incandescent bulbs.

Hardly any 5-phosphor coating CFLs are sold in Denmark because producers and suppliers don't consider that there will be any particular demand for them.

Unfortunately, it is not possible to see from the packaging whether a bulb is tri-phosphor or 5-phosphor.

Colour temperature
The colour temperature of an A-rated bulb indicates whether it is warm or cold.

The colour temperature describes the light’s individual colour and indicates whether the light is ‘warm’ or ‘cold’, similar to how a white wall appears warm white (whitish/yellowish) or cold white (blue/white). Colour temperature is denoted in Kelvins (K) on a scale from 0–10,000 K.

In most indoor situations, only the intervals between 2,600 K and 4,000 K are of practical interest. ‘Warm’ light has the lowest colour temperature. For example, a conventional bulb has a colour temperature of 2,700 K and therefore emits a rather ‘warm’ light. A-rated energy saving bulbs have a colour temperature of between 2,600 and 3,000 K. Information on the colour temperatures of A-rated energy saving bulbs is shown on the recommended list of A-rated bulbs.

 How A-rated bulbs work

In principle, an A-rated energy saving bulb is a miniature compact fluorescent lamp (CFL) which works in the same way as a fluorescent tube.

A coating inside the energy saving bulb causes it to light up
A-rated bulbs operate on the basis that a coating on the inside of the bulb is stimulated by an electrical current which is, in turn, discharged by a HF (high frequency) electronic ballast mounted in the base of the bulb. Conversely, a conventional incandescent bulb produces light by means of a metal filament inside the bulb which heats up so much that it glows.

Different shapes and sizes
A-rated energy saving bulbs come in many different shapes and sizes: bullet, flood, globe, spiral, torpedo, traditional, etc.

An A-shape bulb, which is similar to an ordinary incandescent bulb, typically has an off-white (opaline) plastic or glass envelope over the mini CFL.

Electronics in A-rated bulbs
Like fluorescent tubes, energy saving bulbs make use of a particular technology. This is often referred to as ‘electronic’ even though the correct term is actually ‘electronic ballast’.

In most cases, the miniature fluorescent tube is built, as a unit, into the base of the bulb along with the electronic ballast. But you can also find A-rated energy saving bulbs where the electronic ballast and the fluorescent tube are separated into 2 different units.

A-rated energy saving bulbs take a little longer to light up
When you switch on the light you will find that some A-rated energy bulbs take a little longer to light up compared with incandescent bulbs. Also, it takes a little longer before A-rated bulbs emit their full light intensity.

A-rated energy saving bulbs fitted to lamps with dimmers
You can buy A-rated bulbs that can be dimmed. If this is the case, the information will be shown on the packaging. You should therefore check the packaging to see whether the A-rated bulb is suitable for lamps that can be dimmed.

2 different types of dimmable A-rated bulbs are available:

• One type can be dimmed using a standard light dimmer.
• Another type is one which is activated by special pressure combinations on the switch. Look at the packaging or the printed instructions supplied to see which combinations you should use.

A-rated bulbs do not fail when the voltage changes
A-rated bulbs are not affected by variations in mains voltage that occur in most homes as a result of the building’s location in relation to an electricity substation. Excessive voltage considerably reduces an incandescent bulb’s life; conversely, lower voltage prolongs a bulb’s life, but decreases the light emitted by the bulb.