The architecture of light: architectural lighting design concepts and techniques. A textbook of procedures and practices for the architect, interior designer and lighting designer pdfdrive com

8 = CRI in the 80’s: This is typical and reasonable to use in most day-to- day applications.
9 = CRI in the 90’s: This is very desirable for color critical environments, but also relatively expensive.
The second component of the code lies in the last two digits. These two numbers are indicative of the Color Temperature in degrees Kelvin. The system breaks down like this:
28 = Color Temperature of 2800K = warm (imitating the color of incandescent sources);
30 = Color temperature of 3000K = neutral (imitating the color of halogen sources);
35 = Color Temperature of 3500K = slightly-cool; 41 = Color Temperature of 4100K = cool;
50 = Color Temperature of 5000K = very-cool;
Figure 8.17 Most fluorescent and HID products are labeled with a three digit code expressing color rendering index and color temperature.
Keep in mind that color temperatures are really meaningful only as guidelines within a family of products. One brand of 2800K fluorescent lamp may not look like another brand of 2800K fluorescent lamp and will certainly not look like a 2800K Metal halide lamp nor the incandescent lamp it is trying to imitate.
Source Efficacy Estimates
Identifying source technologies with their general efficacies or efficiencies is a useful and often neglected piece of information. In some lighting design guides, it is a recommended practice to design appropriate light levels for spaces based on a watts-per-square-foot density of installed luminaires. This practice tends to
be tactically deficient. Designing light on a power density basis is ignorant of the different efficacies of the different source technologies. It can lead to uninspired designs of flat, even illuminance levels where they may not be welcome. The closest thing to designing to a density is the Lumen Method Calculation which recommends light density based on lumens per square foot (we will discuss calculation methods in Chapter 20). For the time being, we will introduce a basic set of numbers that will paint an approximate but useful picture of how the most common electric light sources compare to one another in terms of efficacy (light out compared to electricity in). As design progresses, it is advisable to know the efficacy of the specific product being considered. For schematic planning phases and basic comparisons, the rough approximations for the source types below can be used:
Standard incandescent efficacy = 10 lumens per watt (lpw); Halogen incandescent efficacy = 15 lumens per watt (lpw); Fluorescent and HID efficacy = 70 lumens per watt (lpw); LED efficacy = 50-90 lumens per watt (lpw);
This simple table shows why we tend to group all of our high-efficacy sources together. It also illustrates why fluorescent, HID and LED sources are so desirable when compared to the efficacies of incandescent and halogen products that they can replace. If you can make a mental note of these four numbers, you will have an invaluable foundation for visualizing, estimating, and calculating lighting effects.
All of these properties together give the user fairly good insight into
making lamp decisions. Lamp literature is also, thankfully, more straight- forward than that of luminaires. By grasping the basic concepts of color rendering, color temperature and efficiency, one is much better prepared to make decisions about suitable sources for accomplishing lighting goals.