Civil Engineering Reference
In-Depth Information
Table 14.2
Average
values of reflectance
coefficients for different
materials and surfaces
Surface
Reflectance range (%)
Silver
92
Aluminum
70-60
Inox iron
65-55
White paint
90-70
White paper
80-70
White wall
90-70
Wood
30-20
Floor
60-20
Table 14.3
Chromaticity
of light sources
Source
Color temperature K
Daylight with blue sky
15,000-25,000
Overcast sky
5,000-15,000
Sunlight at noon
5,000
Early-morning sunlight
4,500
Sunlight at sunrise
1,700
Incandescent lamps
2,500-3,500
Fluorescent lamps
3,000-6,500
High-pressure sodium
2,000-2,500
High-pressure metal halide
3,500-4,500
LED
3,000-6,000
Table 14.4
Suggested
color rendering for
typical applications
Color rendering
Suggested applications
90
High-precision tasks, museum
80-90 warm tones
House, hospital, offices, school
80-90 cool tones
Textile, printing, mechanical engineering
60-80
Manufacturing industries
40-60
Heavy industries
20-40
In cases without particular requirements
14.3.1 Incandescent Lamps
Incandescent lamps consist of a resistive filament inside an evacuated glass bulb
containing a trace of an inert gas. Electric current passing through the filament
produces light. In a typical incandescent lamp about 5 % of the energy is
converted into the visible spectrum, while the balance is radiated as infrared
energy and heat. These lamps have a relatively short life (less than 2,000 h),
because the filament gradually evaporates, reducing its diameter and increasing its
resistance. This also reduces the light output to about 80 % of the rated lumens at
the end of the life cycle. Incandescent lamps do not require ballast. Typical values
are as follows: lamp efficiency 10-15 lm/W, color temperature 2,800 K, and color
rendering 100.
