1.
Can I wash my Spectralon Reflectance Standard? If so, what method
do you recommend?
Yes, Spectralon can be cleaned, however, it should be carefully
handled much the same as other optical standards. Although the
material is very durable, care must be taken to prevent contaminants
such as finger oils from contacting the surface. Always wear
clean cotton gloves when handling Spectralon. The following
cleaning procedure is for OPTICAL GRADE Spectralon only. If
the material is lightly soiled, it may be air brushed with a
jet of clean dry air or nitrogen. DO NOT USE Freon. Spectralon
with reflectance values greater than 10% can be cleaned by sanding
under running water. Reflectance values less than 10% should
be dry sanded. Use a 220-240 grit waterproof emery cloth and
lightly sand the surface until it is totally hydrophobic (water
beads and runs off immediately). Blow dry with clean air or
nitrogen or allow the material to air dry. If the material requires
high resistance to deep UV radiation, the piece should be prepared
as above, then either of the following two treatments performed:
1. Flush the Spectralon piece with >18_ distilled, deionized
water for 24 hours.
2. Vacuum bake the Spectralon piece at 75° C for a 12-hour period at a vacuum
of 1 Torr or less, then purge the vacuum oven with clean dry air or nitrogen.
Care and Handling Instructions for Labsphere Coatings and Materials are available
in pdf file format in our Technical Information Section.
2.
Are your reflectance standard calibrations traceable to a national
laboratory?
Yes, Spectralon reflectance standards are directly traceable
to the National Institute of Standards and Technology (NIST).
All calibrated reflectance standards are supplied with a calibration
certificate.
3.
What is the recommended re-calibration interval for your reflectance
standards?
Labsphere recommends yearly re-calibration of your laboratory
standards to maintain their stability.
4.
Can Spectralon material be purchased in rods or blocks for machining
at our own facility for prototype experiments?
Spectralon may be purchased in small quantities of unmachined
blocks for prototype development. The machining requirements
for Spectralon are quite stringent due to the unique nature
of the material. Considerations such as contamination from grease
and oil, lubricant and cooling requirements, and machining speed
must all be taken into account. Labsphere has a fully dedicated
Spectralon machine shop, therefore, we generally recommend customers
take advantage of our expertise in machining Spectralon, and
allow us to provide prototype services. Our optical and mechanical
designers work closely with our customers to provide products
to meet their needs. If the product is of proprietary nature,
we will execute a non-disclosure agreement to protect the confidentiality
of the design.
5.
We are interested in using your WRC-680 White Reflectance coating
in a product we manufacture. Will it adhere to polished aluminum?
WRC-680 white reflectance may be applied to most metal, plastic,
and glass surfaces that are properly cleaned and roughened by
mechanical means. We do not recommend applying WRC-680 directly
onto a polished aluminum surface, as you will experience flaking
or chipping. We recommend you consult with a Labsphere applications
specialist to discuss your application.
6.
We have a 10-inch diameter-integrating sphere with a 4-inch
diameter exit port. What is the typical uniformity of radiance
at the output of the integrating sphere? What factors effect
this? Can the performance be improved?
The uniformity (measured with a spot meter focused on the plane
of the exit port and with a numerical aperture of 0.125) will
be approximately 98%. Several small light sources placed around
the inside of the exit port will improve this. In addition,
the actual viewing geometry may see better unifomity (infinite
conjugates, for example). The uniformity is affected by the
reflectance of the coating, the lambertian character of the
coating, the placement of the light sources, the geometrical
distribution of the light from each source, and the viewing
geometry.
7.
What set up do you recommend for measuring the photometric and
radiometric flux of LEDs? We will be measuring LEDs of all types,
including lensed, flat and bare LEDs.
The quickest and least expensive method for measuring the flux
from an LED (or other light source) is an integrating sphere.
The sphere is calibrated with a source of known flux and then
used to measure the flux of the LED. The same precautions to
deal with substitution error must be taken with LEDs as with
any other light source. Other measuring methods include gonio-photometers
and polished hemi-ellipsoids.
8.
I have a group of lamps that need to be measured for total luminous
flux, how do I determine what size integrating sphere to use?
There are two important factors in selecting an integrating
sphere: lamp power and lamp physical size. The smallest lamp
measurement sphere that Labsphere makes is a 10-inch diameter
sphere useable for lamps up to 100 watts in power. Above that
limit, the sphere may get too hot and the danger exists of damaging
the sphere coating. The limits for our spheres can be estimated
since this maximum changes as the square of the diameter doubles,
i.e. if the diameter doubles, the maximum power goes up by a
factor of four. The other important factor is lamp size. For
the more ordinary bulbs, the CIE recommendation is that the
integrating sphere be at least ten times the largest dimension
of the bulb and for tubular lamps the diameter be twice the
length of the lamp. It may not be possible to use and integrating
sphere that fits the size recommendation for tubular lamps,
so we do allow for lamps somewhat larger than half the diameter
in length.
9.
What level of uniformity does the typical integrating sphere
uniform source produce?
The prime contributor to output port uniformity of a uniform
source sphere is the ratio of the sphere diameter to the port
diameter. Using a ratio of 3:1 you can expect ±1% uniformity,
with a ratio of 4:1 you will achieve ±5% uniformity.
10.
I am using an integrating sphere to measure the output of a
laser. Why are my measurements higher than expected?
There are a few possibilities here. First, would be that the
detector is only viewing a portion of the sphere and the input
source is illuminating part of the area that the detector is
viewing directly. This is a common error when placing a detector
directly up to a sphere. The field-of-view (FOV) is high and
the chance of having an overlap between source and detector
FOV becomes high. There are a few solutions to this situation
- limiting the FOV or the detector with an aperture, putting
a diffuser over the detector, or baffling. Second, it is possible
that the source is directly incident on the detector itself.
This can be corrected by baffling or by rearranging the source
and detector geometry. Third, it is possible that the source
itself is effecting the sphere throughput. This is typically
a case where the system is calibrated with light entering a
sphere through an open port, but the user places the test source
directly up to the port. If this source is reflective, then
the sphere throughput would increase and the readings would
be higher than expected. The best methods for correcting this
are to move the source away from the input port, or use an auxiliary
correction in which the throughput change is measured and accounted
for in calculating the final measurement.
11.
I am using a lamp measurement sphere to measure the luminous
flux coming from my lamps. Why are my measurements lower than
expected?
Typically, unusually low measurements are due to absorbtion
being added to the sphere. This will generally arise in a lamp
measurement sphere where the test lamp and the socket are large
and potential absorbers and the calibration lamp is small and
less absorbing. The best correction for this is an auxiliary
correction in which the throughput change is measured and accounted
for in calculating the final measurement.
12.
I have a Labsphere SC-5500 System Control that I am trying to
integrate into our DAQ system in Labview. Do you have a set
of GPIB commands available for this unit?
The commands used via the IEEE-488 interface are the
same as the commands used via the serial port. Typically, the
SC-5500 is at IEEE address 10. The IEEE 488.2 command can be
used with the device.
A typical
initialization sequence for the SC-5500 using Labview with IEEE
488 follows:
Note:
Between each command a delay of at least 500msec is recommended.
1. to set
the 4.5 digits send the SC-5500 H1X
2. to set the "autorange" send the SC-5500 AOX
3. to set the "cal 1" send the SC-5500 C1X
4. to turn the "averaging filter on" send the SC-5500 FOX
A typical
read sequence is
1. send
the SC-5500 OÆX in order to take one reading
2. receive the measurement
Note:
when using the IEEE 488.2 receive command the measurement will
return as a string.