The more light is generated by a lamp of a certain wattage, the more efficient this lamp will be.
Economic lighting means that enough light is provided at the time an place, only, when it is needed.
The luminous efficiency in lm/W is, therefore, a measure for the efficiency of all lamps. It will be quoted either for the lamp itself - as lamp luminous efficiency - or for the lighting system altogether with all needed control gear as system luminous efficiency.
With lamps in applications similar to household applications such as incandescent lamps the efficiency can be estimated from the energy label (see below for details).
Within professional lighting, lamp manufactureres often do not know which control gear will be employed in the end. Thus, in the lamp catalogues, usually only the mere lamp luminous efficiency is quoted. Taking into account the kind of control gear employed, the user has to calculate the system luminous efficiency by himself.
For the operation of discharge lamps such as fluorescent lamps or high pressure discharge lamps ballasts and starters or ignitors are needed. These operational devices do also consume energy, generate greenhouse gases and costs and, therefore, are affected by energy saving regulations (see ErP, for example).
In principle, control gear can be classified like this:
- • Conventional ballasts CCG:
- These transformers or chokes are robust with long service life, on the one hand, but they also do have high power losses. If there are technologically sensible alternatives, CCG are not to be used in new installations any more.
- • Low-loss conventional ballasts LLCG:
- For some applications electronic control simply cannot be employed. In this case, especially efficient and high grade conventional ballasts (chokes) must be used.
- • Electronic ballasts ECG:
- ECGs are clearly more efficient than conventional control gear as the built-in circuits have less material and mass and some lamp types like fluorescent lamps have got less input-power. Their service life, however, may be limited due to the kind of parts used (instant start or warm start ballast) or the ambient conditions (like temperature, humidity).
- • Starters:
- Safety starters must be changed with every 4th lamp change, only. So, they need less material and energy being produced.
- • Ignitors, Hot restrike ignitors:
- A hot restrike ignitor must be on stand-by during the whole lamp operation time, therefore, it consumes energy, whereas other ignitors can switch off. Warm start ECGs for fluorescent lamps with cut-off technology switch off the filament electrode heating, so, they save energy and make their service life longer.
Operational efficiency of luminaires:
- In standard conditions, there will be measured which percentage of original lamp luminous flux still comes out of the luminaire. It is determined by the kind of beam control (reflectors) and also by the thermal conditions in the luminaire.
Illumination efficiency:
- The illuminance within the application is measured and put into proportion with the sum of luminous fluxes of all employed lamps. The illuminaton efficiency mainly depends on the distribution of luminous intensities of the luminaire (directly – indirectly), with indirect lighting it also depends on the reflection properties of the room.
Target: high illumination efficiency
High illumination efficiency can be achieved by a light room decoration, positioning of the luminaires according to the intended purpose of the application and, most of all, by a high operational efficiency of the luminaires. Efficient reflector technology and maintenance friendly designs with low affinity to dirt, for example, by using a luminaire with higher protection (min. IP 5x) may have less light losses in the course of time. Therefore, less energy will be consumed in the end and the maintenance intervals may even be made longer.
Mains voltage lamps for light generation at home must show the so-called energy label when sold. This affects incandescent lamps, energy saving lamps and fluorescent lamps without reflector with wattage over 4W and luminous flux less than 6500lm.
Lamps should be put in class A, when:
- ____________
- W ≤ 0,15 √Φ + 0,0097·Φ (fluorescent lamps without integral ballast)
- ____________
- W ≤ 0,24 √Φ + 0,0103·Φ (other lamps)
- with W = lamp power in W and Φ = luminous flux in lm
If a lamp cannot be put into class A, a reference wattage WR has to be calculated.
- ___________
- WR = 0,88 √ Φ + 0,049·Φ (for Φ > 34 lm)
- WR = 0,02·Φ (for Φ ≤ 34 lm)
From there, the energy efficiency index is determined:
- EI = W / WR
The energy efficiency class (energy label B – G) can be taken from the following table, then:
Energylabel, class EI Energy efficiency index
- B <60%
- C 80%
- D 95%
- E 110%
- F 130%
- G ≥ 130%
When the overall efficiency of a lighting installation should be increased noticeably, then besides efficient operational gear, technology for operation as and when required may be employed such as presence control or power reduction. These, however, need exact planning, as fault free function can only be guaranteed if operation and gear (dimmer, motion detector) have been toned in exactly with the lamp technology in use. Furthermore, the functionalities and possibilities of intervention could decide over the acceptance of the whole system.
The best known system in this respect is daylight control with presence detection which needs dimmable and controllable ECGs. Thus, illumination within the room and also during the day can be kept about constant. Moreover, some different combinations of technologies can be employed (not for all lamp types!) like motion detection, time switches, dimming or half-light by night.
Purpose of application, conditions of the room and further requirements, e.g. emotional or health (circadian rhythm, colour sequences, constant light etc.), costs, maintenance characteristics and so on must be considered when planning a lighting installation sensibly. According ot that, technologies and components can be chosen.
With lamps it not just brightness one needs to focus on but the art is to find the right compromise between luminous efficiency and colour rendering. For luminaires light distribution curve, temperature considerations, mounting and maintenance such as emergency lighting have to be kept in mind.
The chosen light sources - lamps and luminaires/ fixtures - and the known room parameters then can go into the planning process which can be accomplished with certain software. The results will be depicted in numbers, as graphics and - depending on the kind of software - even photo-realistic.