Environmental Engineering Reference
In-Depth Information
6.2.10 Day Lighting by Top Lighting
There shall be a minimum
fenestration area
providing day lighting by
top
lighting
for large enclosed spaces. In buildings three stories and less above
grade, conditioned or unconditioned enclosed spaces that are greater than
2000 m
2
directly under a
roof
with a finished ceiling height greater than 4 m
and that have a
lighting power allowance
for general lighting equal to or greater
than 5.5 W/m
2
, shall comply with the following.
6.2.10.1 Minimum Daylight Zone by Top Lighting
A minimum of 50% of the floor area directly under a
roof
in spaces with a
lighting power density or
lighting power allowance
greater than 5 W/m
2
shall
be in the
daylight zone
. Areas that are daylit shall have a minimum
top lighting
area to
daylight zone
area ratio as shown in Table 6.2. For purposes of compli-
ance with Table 6.2, the greater of the space lighting power density and the
space
lighting power allowance
shall be used.
6.2.10.2 Skylight Characteristics
Skylights
used to comply with Section 6.2.10.1 shall have a glazing material
or diffuser that has a measured haze value greater than 90%, tested accord-
ing to ASTM D1003 (notwithstanding its scope) or another test method
approved by the
authority having jurisdiction
. Exceptions are for
skylights
with
a measured haze value less than or equal to 90% whose combined area does
not exceed 5% of the total
skylight
area.
Skylights
are capable of preventing direct sunlight from entering the occu-
pied space below the well during occupied hours. This shall be accomplished
using one or more of the following:
1. Orientation
2. Automated shading or diffusing devices
3. Diffusers
4. Fixed internal or external baffles
TABLE 6.2
Minimum Top Lighting Area
General Lighting Power
Density or Lighting Power
Allowances in Daylight Zone
Minimum Top Lighting Area
to Daylight Zone Area Ratio
W/m
2
14 W/m
2
< LPD
3.6%
10 W/m
2
< LPD < 14 W/m
2
3.3%
5 W/m
2
< LPD < 10 W/m
2
3.0%
