Lighttex Daylighting Study Test Description

Test Room (AGI32 Lighting Modeling)

105.1

105.5 (105.2)[1]

105.3

105.4

Room Dimension

30’ x 30’ x 15’

Window/Skylight Dimension

10’ x 10’

Window Orientation
Top
center of roof
South (North)
2.5’ above floor
East
2.5’ above floor
West
2.5’ above floor

Window/Skylight Covering Size
3"(2"/2.5") x 3"(2"/2.5") x 10' blind/louver (two perpendicular placement),
45º(35º/40º) Lighttex panels with cell size 3"(2"/2.5") x 3"(2"/2.5") x3"

Glazing-to-Floor Ratio (GTF)

11%

Reflectance of Ceiling

0.8

Reflectance of Walls

0.5

Reflectance of Floor

0.2

Glazing Efficiency

70%

Fabric Reflectance

90%

Illuminance Measuring Points Placement
Foot Candle meters 2.5' high above floor, 2' away from each other

Site Location
Sydney, Australia, -33s52, -151e13; Singapore city, Singapore, 1n1612, -103e51; Hong Kong, China, 22n15, -114e10; Phoenix, Arizona, US, 33n27, 112w04; Barcelona, Spain, 41n2248, -2e1048 and Edmonton, AB, Canada, 53n33, 113w2812.

Dates and Time

07:00am – 07:00pm, March 21st, June 21st, September 21st and December 21st

Sky Conditions
Clear Sky, Overcast
  • Method Description
    • Direct Sun Blocking Percentage
      For daylight sources, direct sunlight is what is best to avoid while skylight and reflected light are generally good.

      Blocking of direct sunlight by Lighttex can be determined from simple geometry (see the diagram below). When the Lighttex material directly faces the sun, there is no blocking. As the angle between the sun direction and the material increases, so does the amount of blocking.

      The angle at which full (that is, 100%) blocking occurs depends on the cell depth and width.

      Expectedly, the lower the Lighttex degree, meaning the denser the grid is, the more direct sunlight is blocked.
      As an alternative, regular blind/louvers can sometimes work almost as well as Lighttex. This is determined by its placement and the sun position changing in a period in a specific city. In some cities such as Sydney, Australia, blind/louvers need to shift between vertical and horizontal several times to achieve an acceptable sun blocking level while with Lighttex (please see result in next section), we achieve better direct sun blocking. Lighttex provides the direct sun blocking benefit of both horizontal and vertical blind/louvers.
    • Illumination Level – Foot Candle
      The lighting level in test room with Lighttex or other window coverings is not being addressed here due to the non-continuousness nature of computer simulation. The selection of reflectance and mesh level of each lighting surface makes significant difference of lighting level. Only illuminance deviation is what is concerned in this case.

      Illumination evenness, one factor of light quality, is addressed below by the foot candle difference between average light level of an illuminating area and the light level of 68% of this area. For example, assume there are 100 light meters in a room. The average of all the readings is 100 foot candles. Suppose evenness is 20 foot candles. This means, that readings of 68 foot candle meters are in the range from 80 to 120 foot candles. Visually the brightness of 68% of this room is 20 candles of light difference from the overall average 100 foot candles of light.
    • Work Plane Illumination Evenness – Standard Deviation
      Illumination evenness is defined as standard deviation of a set of foot candle meter readings. In these square test rooms, each evaluation line consists of 15 measuring points, making 225 points on entire work plane. One standard deviation away from mean in either direction accounts for around 68% of points, roughly 10 for each evaluation line while 153 for entire work plane; two standard deviations away from the mean account for around 95% of points; And three standard deviations account for 99% of points. The formula of standard deviation is:
      The less the illuminance deviation is, the more even the light is. Ideally the illumination is totally balanced when deviation is equal to zero. In real life, lighting level deviation around 50 foot candles or less in a room is acceptable for normal activity such as office work or drawing.

      Theoretically, the more direct sun is blocked, the more even the lighting is. This is because as the direct sun is blocked it is redirected as diffused light. In our computer simulation and in real life, illuminance is measured by specifically placed light meters so that part or all of the hot spots might be missed. What we are concerned with is the lighting evenness comparison between Lighttex and blind/louvers. Since Lighttex basically is blind/louvers with another one perpendicularly installed, the smaller hot spots do not go beyond both the hot strips generated by blind Direct Sun/louvers either horizontal or vertical. If the light meters catch hot points with Lighttex installed, they must also catch hot points with blind/louvers, either horizontal or vertical, installed; but they do not necessarily catch hot points generated by Lighttex when they catch hot points generated by blind/louvers. Lighttex always blocks more direct sun than blind/louvers due to its two-directional nature so that daylighting is more uniform.
[1] This column means test room with a side window orientation which exposes to daylight the longest. It is a South facing window in North hemisphere and a North facing window in South hemisphere.


© 2005 Lighttex Canada, Inc.