Dome Shape Matters
See the attached third party laboratory report of a photometric light test conducted in cooperation with CCL, Construction Consulting Laboratory
West on a Bristolite 5’ x 6” Quasar prismatic skylight and a competing 5’ x 6’ prismatic skylight. The purpose of the test was to determine
whether dome shape affects the light transmission of similar skylights using similar glazing material. Both units tested were stock, standard
units for the particular model and manufacturer represented.
The Bristolite unit utilizes a computer generated, radial triarch, shape for the outer dome and a simple bubble shape for the inner dome as
shown in the following illustrations 1.0 and 2.0.
Illustration 1.0
Quasar Radial Triarch Shape Outer Dome
Illustration 2.0
Quasar Bubble Shape Inner Dome
The competing prismatic skylight unit utilizes a highly complex, multi-ribbed, shape for both the outer and inner dome as shown in illustration
3.0 below.
Illustration 3.0
Numerous ribs with steep shoulders and tight radii make this dome shape capable of utilizing thinner glazing but not without compromising light
transmission.
Prior to photometric testing, field observation of the two skylights in actual installations revealed a stark contrast in illumination . and
illumination consistency as depicted in the following photographs 1.0 and 2.0.
Photograph 1.0 Bristolite Quasar installed, in-service
Photo taken at Noon on 12/21/2010 in Orange County, CA
Note the consistent level of highly diffused light.
Photograph 2.0 Competing prismatic skylight installed, in-service
Photo taken at Noon on 12/21/2010 in Orange County, CA.
Note the heavy shadowing caused by light passing through multiple layers of the outer and inner dome due shape. to the complex radical dome
Based on inspection of the contrasting dome designs and heavy shadowing of the installed competing prismatic skylight unit it was theorized
that shape of both the outer and inner dome may have a significant impact on the amount of light a skylight may transmit to an interior building
space. In review of the test data, one can see that as measured in five degree increments from zero degrees (dawn) to eighty degrees (near noon)
the competing prismatic skylight unit transmits more light than Quasar from 0 degrees to 30 degrees (approx. dawn to 9:00AM). After 30 degrees
and through 80 degrees (approx. Noon) the Quasar transmits more light. For the total test, Quasar transmitted 574.5 lx while the competing prismatic
skylight unit transmitted 494.0 lx. In total the Bristolite Quasar transmitted 16.3% more light than the competing prismatic skylight unit.
Since both the Quasar and competing prismatic skylight units are symmetrical from end-to-end and side-to-side the photometric test would have
produced the same result had the test been carried out from 0 zero degrees (dawn) to 0 zero degrees (dusk).
Illustrations 5.0 and 6.0 that follow depict an explanation of why the Quasar transmits 16.3% more light than the competing prismatic skylight
unit.
Illustration 5.0
Light Passing Through Quasar’ Radial Triarch and Bubble Shape Domes
From dawn to dusk sunlight never passes throughmore than two layers of glazing on the Quasar unit.
Illustration 6.0
Light passing through the competing prismatic skylight highly Both the outer and inner domes have the same shape. complex, ribbed shape domes.
A large portion of the available sunlight during the day must pass through multiple layers of the glazing and the twenty-four 1.625” long rib
shoulders on the competing prismatic skylight unit.
As you can see between thirty degrees (approx. 9:00AM) and one hundred eighty degrees (approx. 3:00PM) a good portion of the available sunlight
must pass through up to eight layers of glazing and travel through the twenty-four 1.625” length of the shoulders of the steep ribs of both
the outer and inner domes. This is the cause of the darkened areas in the skylight viewing area as shown in the previous Photograph 2.0. These
darkened areas, called shadows are transmitting very low levels of light to the interior of the building.
Conclusions:
- Dome shape can have a significant effect on the light transmission of similar skylights using similar glazing material.
- Simple shapes that provide the necessary strength for a dome to withstand the elements of weather and meet OSHA fall protection standards are
best.
- Overly complex and or radical dome shapes so designed to allow the manufacturer to use thinner and less expensive dome material can adversely
affect light transmission performance.
- While all skylight manufacturers report Visible Light Transmission (VLT) for their skylights and most architects and building owners specify
a minimum acceptable VLT for skylights in their projects; laboratory test for VLT do not necessarily reflect the true light transmission of
a formed dome in a complete skylight in service. Most laboratories that offer VLT testing, test light transmission on 4” by 4” unformed samples
of the glazing material submitted by the skylight manufacturer. While these laboratories, reporting VLT with a number from 0 to 100 do provide
useful information, it should be understood that the laboratory VLT test does not have the means to account for variations in light transmission
performance due to dome shape. As clearly demonstrated in this test, dome shape can significantly affect the light transmission of similar skylights
using similar glazing material.
End of report summary
Competitor Challenge: If a customer or potential customer with competing prismatic skylights installed
on one of their facilities would like to see a side-by-side comparison of the competing prismatic skylight and Quasar for themselves, from the
floor of their facility, following is our offer. We will ship a Quasar skylight to their facility and send a field engineer to their facility
to replace one competing prismatic skylight with our Quasar skylight for their personal observation. This service is offered FREE with
no charge and made available at the customer’s convenience. Our Engineer will be equipped to assist in measuring and comparing light transmission and solar induced heat gain.
We want them to see the Quasar difference in their facility with their own eyes.
Continue to the next page to see the third party test report.
