An
important issue to consider when using any optical
design tool is accuracy. As a designer, you need
to trust that your design tool is accurately predicting
the distribution of light within your model. Time
and money is lost when software tools fail to produce
accurate results. We at LTI understand this issue
first hand. We use Photopia on a daily basis to design
products for our clients. Based on our experience,
and the experience of other Photopia users, we've
compiled a few case studies to illustrate how accurate
Photopia
predicts the distribution of light.
Preface |
Photopia’s
accuracy is well proven over its many
years of use. Both LTI and our customers
have
made comparisons between measured and
predicted photometric distributions and
as long as
the physical luminaire matches the
Photopia model in all respects, the results
are
very accurate. Note however, that Photopia
makes no attempt to model changes in lamp
lumen output as a result of thermal effects.
Therefore designs that employ temperature
sensitive lamps may show significant differences
between the predicted and the measured total
luminaire efficiency (LOR) since Photopia
is only predicting the “optical efficiency” not
the “thermal efficiency” of the
design.
When
analyzing a design in Photopia, it is important
that the Photopia
model match the physical model in all respects,
including:
-
Optical
Component Geometry – make
sure reflector and lens shapes are
accurately manufactured, which they often
are not especially for sheet metal
parts.
-
Optical
Surface Properties – make sure
the materials used in Photopia match
those used in the physical parts.
-
Lamp
Type and Modeled Orientation – in
the case of MH lamps care must be
taken because the arc shape
and position can shift as
the lamp
is aimed in
different orientations.
Obviously, if the physical
model does not match the Photopia model,
the accuracy suffers.
If you plan to distribute Photopia generated photometric files to your customers, then please see this FAQ topic for additional information.
|
Example
: Paracube Troffer |
 |
Description: 2'
x 4' Paracube Troffer, White Painted
Reflector, 3 T8 Lamps. Photopia model
used 87% white paint, 2,000,000 rays
with 10 reflections.
Efficiency: Photopia
= 65.0% vs. Measured = 63.1%
All
measured data supplied by Lighting
Sciences, Canada. |
|
Example:
Roadway Luminaire |
 |
Description: Roadway
luminaire with a hydroformed reflector
using a 150W SON-T HPS lamp.
BRDF data for the specific reflector
finish was measured at LTI's lab and
used in the analysis. |
Measured Distribution (shaded Plot showing
illuminance at a plane) |
|
Photopia
Predicted Distribution (same plot settings
as above) |
|
|
Additional
Information |
For additional information
regarding Photopia's accuracy and the factors
that affect both the measured and predicted
values, please review Appendix C from our
User’s Guide below. For comments on
Photopia and its accuracy from some of our
customers, see the Photopia User Reviews
link below.
Photopia : Appendix C
Photopia User Reviews
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