According to the characteristics and requirements of modern office space, as well as the understanding and grasp of lighting sources, electrical technology and products, the framework of designers' lighting design in the office is basically established. Today we look at how to choose the right lighting for office lighting.
In lighting recommendation, the lighting designer's role is like a headhunter. She is responsible for applying the most suitable product recommendation to the most suitable space. The last product, can not be competent for this space, just like this person is competent for this position. Unlike headhunters, headhunters are not responsible for designing job responsibilities. They only find the right people according to their needs. The designer is the first person responsible for shaping the light environment of the space itself. Moreover, the case itself will become a designer. One of the products, therefore, should bear more important responsibilities.
We have already evaluated the color temperature, color rendering, and energy efficiency of the light source. If we regard this part as the candidate’s knowledge reserve, then today we look at the luminaire, which is an assessment of whether or not he is competent for the job. (All metaphors are lame, haha, make do with understanding ~) Of course, we designers often have, as well as the size, shape, material, workmanship requirements of the lamps, not included in this article.
For modern office space, the main aspects of lamp evaluation involve: light output mode, light extraction efficiency, light distribution curve, and lamp brightness limit curve, which are mainly related to space energy efficiency level, glare control, and brightness distribution. The latter two are directly related to Visual comfort. We use the lamp panel, the most commonly used office space, as an example for analysis.
Fish and bear's paw can not have both, the color rendering and luminous efficiency of the light source is a pair of contradiction, the utilization efficiency and comfort of the light are also a pair of family members.
Spectral light efficiency curve
[Insert] Why is the color rendering and light efficiency of the light source a contradiction?
According to the above spectral light efficiency curve (see function), the human eye feels the most sensitive to the green light at 555 nm. It is worth noting that when the radiated power of the green light at 555nm is 1W, the emitted light flux is 683lm. At this time, the luminous flux generated by the 1W power is the largest, that is, 1lm is equivalent to 1/683W, which is required for generating 1lm of luminous flux. The minimum power.
We can see that if the light efficiency is required, the wavelength of the radiation of the light source needs to be concentrated to 555 nm as much as possible. However, the requirement of color rendering is that the radiation wavelength of the light source needs to be distributed in each band.
Let's look at this pair of friends: the efficiency and comfort of light. From the perspective of light utilization efficiency, we hope that all light can be used directly on the work surface, but in terms of comfort, we like the light in the space (no matter whether it is homogeneous light or more interesting brightness distribution). ).
When selecting lamps, we need to balance the two, and then we can determine the lighting methods of the lamps:
If the office lighting is differentiated by direct/indirect lighting, it is not difficult to read the nine icons above according to the lighting examples below. The difference between them can be described by one parameter: FFR (relative luminous flux ratio: down-illumination flux DLOR/up-illumination flux ULOR).
When FFR = 0, it means that the lamp has only a down light. This can be a completely direct diffuse luminaire, usually a grille luminaire, although such a luminaire can provide a high direct ratio and produce high luminous efficacy in the work area, but also due to its high contrast And create a depressing atmosphere. The luminaire can be embedded, ceiling mounted or suspended.
When FFR=0.1, this type of lamp cannot be embedded or installed by ceiling. It produces a small amount of overhead light, which helps to relieve the repressed atmosphere created by the purely downward light. In addition, it softens the shadows.
When FFR=1, the ratio of uplight and downlight generated by the luminaire is the same, and at this time, the term “direct/indirect ratio” will become “indirect/direct ratio”. The shadows are much softer and the contrast is reduced, but the lamp efficiency is slightly lower than the lamp with a high direct illumination ratio.
When FFR=10, the luminaire is almost purely light-emitting. Only a small part of the luminaire emits light and is usually covered or scattered. The pattern of downlight is different, and most of it is also scattered. The lighting effect depends on the finish of the ceiling, the spacing between the fixtures, and the distance between the fixture and the ceiling.
When FFR = ∞, a purely upward-illuminating luminaire produces a special scattering effect with a very low contrast and a monotonous tendency. Again, the final effect depends primarily on the finish of the ceiling, the spacing between the fixtures, and the distance between the fixture and the ceiling.
At the same time, in addition to the impact on the utilization efficiency, the lighting of the lamps also determines the visibility of the light source. Combining the FFR with the visibility of the light source, we can make an assessment of comfort:
According to the study, the proportion of indirect light at different levels of illumination has different effects on computer and desktop reading.
Similarly, the impact of visual impact on visual psychology created by indirect lighting is related to the level of illuminance in making employees value work, motivation, and enjoyment. It is not better.
Regarding the consideration of comfort, while fully utilizing indirect light, we also need to strictly limit glare so as not to affect work efficiency in visual physiology.
One of the ways to limit direct glare is to control the protection angle of the lamp, which is the advantage of the downlight grille lamp. According to the seated perspective, the protection angle of the office lamp is preferably controlled at 30° or more.
GB50034 also makes requirements for the shading angle of direct type lamps:
However, for a luminaire with a white grid or a mirror-controlled aluminum grid but with poor light control, the simple geometrical principle is not sufficient to reflect the real problem. Considering the use of visual display terminals in modern offices, it is necessary to further look at the surface brightness limit curve of the lamps.
GB50034 is so required:
Drawing on CIBSE's Cat2 standard:
According to the actual situation and experience of the current visual display terminal, the recommended practice is as follows: