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Technical Information
 

 

ABOUT REFLECTANCE MATERIALS AND COATINGS

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.

ABOUT INTEGRATING SPHERES

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 OX 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.

 

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