8/7/2019 The Comedy of Errors of Light Booths and Its Calibration

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The Comedy of Errors of Light

Booths and its Calibration

Today I want to write about theerrors committed in calibration of

Light boxes by almost all ISO17025 certified labs in India , andits acceptance by the auditors.

ISO 17025 calls for very strictcalibration , verification andmaintenance of instruments usedfor testing.

I strongly beleive that more bydesign , users of light boxes have

been made to believe that Luxvalue alone need to be calibratedand the Spectral Power Distributionand Color Temperature ( the last 2terms are seldom mentioned byanyone leave alone understand it ).

The reason for this is largely lack ofknowledge of the need to tomeasure these values not only bythe Indian companies that made

low cost light boxes. Not only werethese people ignorant , due to theirpropaganda and the lack ofknowledge even among dyers , Luxmeasurements were considered assufficient measurement.

The choice of Lux as a parameterwas in my view due to 2 reasons ,the measuring instrument is cheapand easy to achieve with

commercial Fl Lamps.

Further ISO 105 A01also does notsay anything about the need tomeasure SPD and CCT , it simplysays 600 Lux and above isconsidered as good for Grey scaleassessments , another mistake

here is no maximum value ismentioned, high lux values canalso cause problems.

So the Light Box makers bought

low cost Lux meters , that is mostlyused in the film industry tomeasure lux at the Heroines faceand started measuring the lightinside the cabinet to be 600 Luxand above and started sellingcertified Light boxes.

The major problem is no one knowwhat lamps were generating the600+ Lux , and it could be

anything D65, F02 F11 etc.

The auditors who were accreditedby NABL ( National accreditationBoard for Testing and calibrationlabs ) also went only by Lux valuesand did not bother to check theSPD or the CCT.

One very much acclaimed Auditoreven dismissed me saying that

SPD and CCT are not required to bemeasured.

So several Indian made light boxedhad D55, CWF TL84 or any lampwith 600 lux and got away ascalibrated light boxes.

This is the the biggest cause fordebates in visual matches as wellas Grey scale values.

Comments and Recommendations.

Please note Light Boxesneed to be calibrated forLux, SPD and CCT.

Refer to AATCC EP 9 formore details on what

http://textilesciences.blogspot.com/2009/09/comedy-of-errors-of-light-booths-and.htmlhttp://textilesciences.blogspot.com/2009/09/comedy-of-errors-of-light-booths-and.htmlhttp://en.wikipedia.org/wiki/Spectral_power_distributionhttp://en.wikipedia.org/wiki/Color_temperaturehttp://en.wikipedia.org/wiki/Spectral_power_distributionhttp://en.wikipedia.org/wiki/Color_temperaturehttp://textilesciences.blogspot.com/2009/09/comedy-of-errors-of-light-booths-and.htmlhttp://textilesciences.blogspot.com/2009/09/comedy-of-errors-of-light-booths-and.html

8/7/2019 The Comedy of Errors of Light Booths and Its Calibration

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must be CCT of the lampsand the desirable Luxvalues.

CIE has full details of theSPD of all the lamps

Calibration has to becarried out every 1000hours of operation or 1year which ever is earlier.

Fluorescent Lamps cannotbe adjusted and need toreplaced with new ones ifthe required values arenot achieved.

Do not be taken in byprice, compliance to

standards andspecification are moreimportant, as Color is thebiggest property based onwhich the Apparelbusiness is done. Rightfrom design to purchaseof a product by aconsumer.

Good Light boxes showthe color as close as it is

in its original state andthere by reduces debates.

Clean the Tubes daily, orfiber keeps accumulatingon the tubes and over aperiod of time changesthe Lux , CCT and SPD .

Paint the Light BoxMunsell N5 or N7 as perthe manufacturersinstructions.