1 Introduction
At present, in lighting engineering design, energy saving requirements have become a particular concern under the premise of ensuring the quantity and quality of lighting. In fact, human beings have an electric light source. The efficiency of practical light sources ranges from a few lumens per watt to more than 100 lumens per watt today. It is a history of human energy pursuit of lighting energy conservation for more than 100 years. The difference is that today's society is developing rapidly and energy consumption is greatly increased. Under the situation of open source and thrifty, and protecting the environment, it is imperative to emphasize lighting energy conservation. The requirements for lighting energy conservation are naturally stricter and higher. The energy-saving design of lighting engineering has become the most basic and important step in lighting energy-saving work. At present, lighting energy-saving standards have been established in several lighting fields, limiting the power consumption of lighting, and using lighting power limits or lighting power density (LPD) limits as one of the most important indicators for measuring the energy saving of lighting systems. This paper mainly analyzes the relationship between LPD and several lighting elements. In addition to the hard indicators such as the quantity and quality of lighting in the lighting system design, we should also pay attention to several factors affecting LPD, such as the light distribution characteristics of the lamps (light distribution) ) Selection and so on. Only when selecting the lighting system hardware such as light source, lighting and supporting facilities efficiency, it is possible to achieve the LPD requirements by selecting reasonable lighting system software such as design method, lighting distribution and layout scheme.
2 Determination of LPD
It is well known that the use of lumens in lighting system design or the use of coefficient method to determine design (work) illuminance is the most basic method of lighting design, and its calculation formula is as follows:
Where: η—the number of light sources installed;
W———The rated power of the light source, in watts;
UF—the total luminous flux utilization factor;
MF—the maintenance factor of the lighting equipment;
E————Design illumination, taken from lighting design standards, unit: lx.
It can be clearly seen from (2): N × W/S is the value of the illumination power density to be determined, that is, LPD—the value of the illumination power installed per unit area.
Obviously, N × W/S is related to the design illumination, the luminous efficacy of the light source, the total luminous flux utilization factor and the maintenance factor of the lighting device.
In addition, as can be seen from the first item on the right side of (3), the unit of design illuminance is lumens per square meter, divided by the luminous efficiency η (lumens/watt) of the light source, and its unit is exactly equal to watt/square meter, ie LPD Units, just need to multiply the UF and UM dimensionless coefficients.
As can be seen from (4) [1], LPD, E and UM are all obtained by the lighting designer according to the relevant lighting design standards. η depends not only on the luminous efficacy of the light source, but also on the power loss of lighting accessories, control devices, etc., which can be obtained from the manufacturer, which are relatively fixed parameters.
In formula (4), UF is the only design experience and skill that has lighting designers to influence the correlation coefficient of LPD, and it is inversely proportional. Under the premise of satisfying the quality of lighting, the larger the UF, the smaller the LPD, which means the better the energy saving effect. Conversely, the smaller the UF, the larger the LPD. After obtaining relatively fixed parameters, the UF value is determined reasonably and scientifically, and the LPD value can be determined and the energy saving requirements are met.
3 The relationship between the utilization factor and the luminaire
It is well known that in lighting engineering design, the definition of utilization factor is the ratio of the luminous flux of the light source received on the illuminated surface to the total luminous flux of the light source (for all the light sources on the illuminated surface), so it can be understood as the utilization factor of the light source of the light source. (Multiple reflections are not considered here). Expressed as:
Where, UF total - the total utilization factor of the illuminated surface or the utilization factor of the total luminous flux of the light source
S——the area to be illuminated, unit: square meter ( m2 );
E————The calculated illuminance or measured illuminance, unit: lux (lx);
F total - the luminous flux of all sources used for illumination by the surface, in lumens ( lm).
(5) E × S in the formula, that is, the luminous flux obtained on the illuminated surface can be rewritten as F total × η luminaire × UF luminaire, then ( 5) becomes:
UF luminaires are defined as the ratio of the luminous flux of a luminaire that falls on the illuminated surface to the total luminous flux emitted by the luminaire.
Therefore, it is not difficult to see from equation (6) that the total utilization factor of the lighting system is directly related to the utilization factor of the luminaire. Conversely, the utilization factor of the luminaire also directly affects the total utilization factor of the lighting system, thereby further affecting the energy-saving characteristics of the lighting system. In addition, the maximum value of the total utilization factor of the lighting system is the efficiency of the luminaire. Here, since the light in the overflow area outside the beam angle of the lamp is zero-passed, the utilization factor of the lamp is the luminous flux utilization rate of the lamp.
4 Analysis of luminaire utilization coefficient
According to the relevant lighting design standards, the number of light fluxes entering the illuminated surface is obviously related to the installation height, position and light distribution of the selected lamps (mainly the beam angle and light intensity distribution of the lamps). Moreover, in general, the efficiency of the same kind of luminaire varies with the width and width of the light distribution. The wider the light distribution, the higher the efficiency, but the utilization factor of the luminaire is not necessarily high, even if the quantity and quality requirements of the illumination place are met, It is not necessarily energy efficient, which is especially prominent in the lighting design of stadiums.
This paper intends to analyze the main factors affecting the luminaire utilization factor through simple calculations and cause the attention of lighting designers. To make the calculation simplistic, make some assumptions:
4. 1 The first option
5; The required illumination uniformity is 0.5. 5; The required illumination uniformity is 0. 5;
(2) The selected light source is a 400W high pressure sodium lamp with a luminous efficiency of 105 lm/W (taking into account the power loss of the lighting accessory) and placed above the center of the illuminated surface (as shown in Figure 1);
In Figure 1: L - lamps
H——installation height, unit: m;
R——the maximum projection radius, in meters;
C——Boundary angle, unit: degree.
(3) It is assumed that the selected luminaire is a kind of light source and multiple light distributions, and its efficiency is 70%, and it does not change with the light distribution; it is assumed that the beam light of a plurality of light distributions is also constant, that is, the beam angle can be Change, its beam light is unchanged. In addition, the light intensity value in the beam angle of each type of light distribution is constant, and the light of the lamp is set to zero. This is mainly to highlight the extent to which the beam angle and intensity variability affect the luminaire utilization factor.
The result of this assumption is that some variable factors are fixed, so that the luminaire utilization factor is only related to the installation height of the luminaire and the width of the light distribution.
In this paper, nine kinds of axisymmetric light distributions are selected, as shown in Figure 2. According to the C-type goniometer principle, the beam angle of the light source or the lamp can be obtained.
By calculation, the light intensity value within the angle of each of the light distribution beams can be calculated, as shown in Table 1.