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This guide provides an overview of the light sources/bulbs that Lightyears recommends for its lamps. Understanding the many technical terms found on the packaging of a light source can be difficult. We, therefore, provide here an outline of the three key parameters.

Luminous flux is measured in lumens (lm) and indicates how much light is emitted by the light source/bulb. In the past, power usage (measured in watts) was used as a reference for the quantity of light emitted by a light source. As the incandescent light bulb with a wire filament was being phased out and new substitution technology was entering the market, the previous reference framework was no longer as useful as it had once been. This is because the new luminaire technologies proved to be far more effective than the traditional filament bulb. This is also why a 25W light source can’t be directly compared to various other types because luminous efficacy varies greatly between the types.

The table below provides a rough outline of the power usage in watts (W) and luminous efficacy in lumens (lm) of various luminaire technologies.

Filament bulb

Halogen bulb

Energy-saving bulb

LED bulb

25 W/200 lm

18 W/200 lm

5 W/230 lm

3.5 W/250 lm

40 W/360 lm

28 W/350 lm

8 W/400 lm

5 W/350 lm

60 W/600 lm

42 W/630 lm

11 W/600 lm

7.5 W/600 lm

75 W/800 lm

52 W/840 lm

14 W/800 lm

10 W/800 lm

100 W/1,200 lm

70 W/1,240 lm

20 W/1,150 lm

18 W/1,500 lm

Actually, it makes more sense to speak of the efficacy (output) of luminaire technologies, which is measured in lumens per watt:

Filament bulbs

10 lm/W

Halogen bulbs

15-18 lm/W

Energy-saving bulbs

50-60 lm/W

LED bulbs

70-80 lm/W

The rule of thumb is that energy-saving bulbs have 5-6 times more luminous efficacy per watt, and LED bulbs 7-8 times, than the conventional filament bulb.


Colour temperature tells us how hot or cold a light source is. While blue-spectrum light is perceived as being cool, red-spectrum light is perceived as being hot. Colour temperature is measured in kelvins: the higher the Kelvin rating, the cooler the light. We in the Nordic countries prefer the warm spectrum, which is characterised by a low colour temperature of 2,600 – 3,000 K. The old-fashioned filament bulb has a colour temperature of 2,700 Kelvin.


Colour reproduction indicates the ability of a light source to reproduce colours. Colour reproduction is measured in Ra (or CRI) – the higher the Ra rating, the better the colour reproduction. Halogen and filament bulbs have a Ra rating of almost 100, while energy-saving and LED bulbs have a Ra rating of 80 as a minimum (this is a statutory requirement). Always choose light sources with a high Ra rating for rooms where colour reproduction is particularly important (e.g. the kitchen, dining room and reading lamps).


The choice of a light source depends, not only on the quality of light, but also on its function, power usage and purchase price. All light sources have their pros and cons, but current quality-to-price improvements of LED light sources are so encouraging that LED may be expected to out-compete the other types within just a few years. In return, we’ll be able to enjoy increasing light quality at a lower cost.


LED light sources/bulbs 
LED is short for Light Emitting Diode, i.e. a diode that emits light. LED light sources light up immediately; they consume little energy and typically have a good colour reproduction. A LED light source is relatively expensive, but usually has a very long service life. Most LED light sources are dimmable. They should be recycled because more than 85% of their components can be reused.

HERE’S A GOOD TIP: Choose energy class A+ or A++ bulbs with a service life of 25,000 hours, making sure to choose the right colour temperature (2,600 – 3,000 kelvins indicates a warm-spectrum light).

Energy-saving bulbs/compact fluorescent lamps
An energy-saving bulb consumes little energy, has a long service life, is safe to use and is usually relatively inexpensive. However, it’ll take some time before an energy-saving bulb reaches maximum performance. Not all energy-saving bulbs are dimmable. They must be disposed of with care as they contain mercury.

HERE’S A GOOD TIP: Choose at least an energy class A bulb/lamp, with a minimum service life of 10,000 hours and a Ra rating over 90 if you want good-quality colour reproduction.

Halogen bulbs/halogen incandescent bulbs
A halogen bulb does a very good job in terms of colour reproduction and produces a warm-spectrum light. It lights up immediately and is inexpensive. The bad news is that it consumes a lot of energy, has a short service life and will, therefore, prove expensive in the long term.

HERE’S A GOOD TIP: When your halogen incandescent bulb stops working, consider replacing it with an LED light source.