4. LUMINOUS FLUX
Luminous flux is the quantity of the
energy of the light emitted per
second in all directions. The unit of
luminous flux is lumen (lm).
5. ILLUMINANCE
⢠Illuminance is the
total luminous flux
incident on a surface,
per unit area.
⢠It is a measure of how
much the incident
light illuminates the
surface.
6. LUX
⢠The lux ( lx) is the SI derived unit
of illuminance and luminous
emittance, measuring luminous
flux per unit area. It is equal to
one lumen per square metre.
⢠Illuminance is measured in lux
using LUX METER
8. LUMENS TO WATTS
The amount of light required is expressed in terms of lumens.
But the light bulbs are sold in terms of watts.
9. GLARE
⢠Glare is a visual sensation caused
by excessive and uncontrolled
brightness. It can be disabling or
simply uncomfortable.
⢠Reducing glare is an effective way
to improve the lighting.
10. TYPES OF GLARE
⢠Headlights of oncoming
traffic â direct glare
⢠Headlights in rear view
mirror when driving at night
â indirect glare
11. DAYLIGHT FACTOR⢠The daylight factor (DF) is a very
common and easy to use measure
for the daylight quality in a room.
It describes the ratio of outside
illuminance over inside
illuminance, expressed in
percentage.
⢠The higher the DF, the more
natural light is available in the
room.
⢠DF = 100 * Ein / Eext
12.
13. Average DF Appearance Energy implications
< 2% room looks gloomy Electric lighting needed most of
the day
2% to 5% daylit appearance but artificial
lighting is needed.
Good balance between lighting
and thermal aspects
> 5% Room appears stongly daylit Daytime electric lighting rarely
needed, but potential for
thermal problems
DF AND APPEARANCE, THERMAL
PERFORMANCE
14. DAYLIGHT AUTONOMY
⢠Daylight Autonomy (DA) is the percentage of working hours when lighting needs are
met by daylight alone.
⢠It is measured by comparing daylight illuminance on a work plane to the minimum
requirement over time.
15. UDI
⢠Useful Daylight Illuminances (UDI) also measures a percentage of time
that a space receives adequate daylight, but it also quantifies when the
light levels are too high and too low. UDI is based on three standard bins
18. GLAZING PROPERTIES
They control the amount of daylight, quality of light, and amount of solar
heat gain let into the building They determine the thermal comfort and
visual comfort.
1. Thermal conductance (U-value)
2. Solar Heat Gain Coefficient (SHGC)
3. Visible Light Transmittance (VT)
19.
20. U- VALUE
⢠Thermal transmittance (U-value) measure how much heat is conducted in. The
lower the U-value is, the better the material is as a heat insulator
⢠It is the rate of transfer of heat through a structure divided by the difference in
temperature across that structure.
21. FACTORS INFLUENCING U VALUE
1.AIR GAP
Air is a good insulator of heat
2.NUMBER OF PANES
23. SHGC -SOLAR HEAT GAIN COEFFICIENT
⢠measures how much of the incoming heat from sunlight gets transmitted into the building.
⢠Theoretically, the value ranges between 0 & 1. For real products range from about 0.9 to
0.2.
27. VLT- VISIBLE LIGHT TRANSMITTANCE
⢠The percentage of visible light that passes through a window or other glazing unit is
called the Visible Light Transmittance (VT/ VLT/ LT).
⢠No UV or IR, only visible light
⢠opaque wall -VT of 0%
⢠empty opening - 100%
⢠optimum VT of 30 - 80%.
