Lamp selection for modern office lighting design guide

Xiao Bian believes that in the lighting recommendation, the lighting designer's role is like a headhunter, she is responsible for applying the most appropriate product recommendations to the most suitable space. In the end, this product can be qualified for this space, just like whether this person is qualified for this position. Unlike headhunting, headhunting is not responsible for designing job responsibilities, but finding the right person according to the needs of the owner. The designer is the first person in charge of the light environment of space itself, and then the case itself will become a designer. A product, so it should be assumed to have a more important responsibility.

We have already evaluated the color temperature, color rendering, energy efficiency, etc. of the light source. If this part is regarded as the candidate's knowledge reserve, then today we look at the lighting, which is an ability assessment of whether he is qualified for the job. (All metaphors are lame, haha, make do with understanding~) Of course, what our designers often have, as well as the size, shape, material, and workmanship requirements of the lamps, are not discussed in this article.

For the modern office space, the main aspects of luminaire evaluation involve: the light-emitting mode, the light-emitting efficiency, the light distribution curve and the brightness limit curve of the lamp, which are mainly related to the energy efficiency level of the space, the glare control and the brightness distribution, and the latter two are directly related to Visual comfort. We use the most common lamp panel in office space as an example.

Fish and bear's paw can't have both. The color rendering and luminous efficiency of the light source are a contradiction. The efficiency and comfort of light is also a pair of friends.

Spectral light efficiency curve

Why is the color rendering and light effect of the light source a contradiction?

According to the above spectral light efficiency curve (see function), under the visual vision, the human eye is most sensitive to the 555 nm green light. It is worth noting that when the radiant power of 555nm green light is 1W, the luminous flux is 683lm, and the power of 1W produces the largest luminous flux, that is, 1lm is equivalent to 1/683W, which is required to generate 1lm luminous flux. Minimum power.

We can see that if the luminous efficiency is required to be high, the radiation wavelength of the light source needs to be concentrated as much as possible to 555 nm. However, the requirement for color rendering is that the wavelength of the radiation of the light source needs to be distributed in each wavelength band. SO. . . Desnie!

Let us look at this pair of homes: the efficiency and comfort of light. In terms of light utilization efficiency, we hope that all the light can be directly used on the work surface, but in terms of comfort, we like the light in the space (whether it is homogeneous light or more interesting brightness distribution). ).

When choosing a luminaire, we need to balance between the two, and then we can initially determine the way the luminaire emits light:

If the office fixtures are distinguished by direct/indirect lighting, we can see the nine icons above based on the lighting examples below. The difference between them can be described by one parameter: FFR (relative luminous flux ratio: downlight flux DLOR / uplight flux ULOR).

When FFR=0, it means that the luminaire has only the downlight. This can be a completely direct scatter fixture, usually a grille luminaire, although such a luminaire can provide a high direct ratio and produce high light efficiency in the work area, but also due to its high light and dark contrast. And a repressed atmosphere. Such luminaires can be either built-in, ceiling mounted or suspended.

When FFR = 0.1, this type of luminaire cannot be embedded or installed. It produces a small amount of overhead light that helps to alleviate the oppressive atmosphere created by pure downward light, and it also softens the shadows.

When FFR = 1, the ratio of the upper and lower beams produced 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 luminaires are slightly less efficient than lamps with a high direct illuminance ratio.

When FFR=10, the luminaires are almost purely illuminating, and only a small part of the illuminating light is usually covered or scattered. The mode of the 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-illuminated luminaire produces a special scattering effect with very low contrast and a monotonous tendency. Again, the final result 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, the light-emitting mode of the luminaire not only affects the utilization efficiency, but also determines the visibility of the light source. Combining FFR with source visibility, we can make an assessment of comfort:

According to the study, the proportion of indirect light has different effects on computer and desktop reading under different illumination levels.

Similarly, the visual psychological impact of indirect lighting is related to the level of illuminance in terms of making employees value work, being motivated and pleasing, not as much as possible.

Regarding the comfort considerations, while making full use of indirect light, we also need to strictly limit glare to avoid visual physiology affecting work efficiency.

One of the ways to limit direct glare is to control the protection angle of the luminaire, which is an advantage of the downlight type luminaire. According to the sitting position, the protection angle of the office luminaire is preferably controlled above 30°.

GB50034 also requires the shading angle of direct type lamps:

However, for a luminaire with a white grid or a mirror-mounted aluminum grille with poor light control design, the simple geometric principle is not sufficient to reflect the real problem. Taking into account the use of modern office visual display terminals, it is necessary to further look at the surface brightness limit curve of the luminaire.

GB50034 is so required:

The illustration is as follows:

Drawing on the Cat2 standard of CIBSE:

According to the actual situation and experience of the current visual display terminal, the recommended practices are as follows:

In addition, outside the luminaire itself, the brightness of other light-receiving surfaces in the room also affects the vision. The picture below shows the latest European standards for indoor surface reflectance for design reference.

In general, modern office lighting design is a comprehensive project. In the selection of lamps, it is necessary to consider the energy utilization efficiency, glare control, and also consider the comfort caused by the form of the lamp and the spatial brightness distribution. Visual psychological effects and control in a range of reasonable positive effects.