"Warming up" an instrument, such as the i1Pro, is a very vital step in insuring more accurate measurements. This step is simply turning the instrument on and allowing it to come to thermal equilibrium. Since the i1Pro has no power switch, its power is supplied from the USB connection, plugging in the instrument turns it on. A spectrophotometer such as the i1Pro uses a linear sensor to make the spectral measurements. One source of noise from these sensors is the dark noise, a signal produced by the device without any light hitting the sensor. This electrical signal can be generated by heat as well as light, so this unlit sensor signal is often called "thermal noise". As part of the calibration process, when the i1Pro is placed on its reference tile, the dark signal is measured for each sensor pixel and stored, later to be subtracted from the signal so the measurement. It should be understood that this dark noise has a steady portion and a random portion and that the calibration will serve to remove the steady portion only. If an i1Pro is immediately calibrated and used before it thermally equilibrates, this dark current value, the steady state part of the signal, can change significantly as the instrument warms up, making the measurements increasingly less accurate. By allowing the i1Pro to warm up, the device produces a more steady dark current so the measurements are more accurate. One other item that should be mentioned is thermal drift. As the instrument is used, there can be a change in the dark current produced in the sensor. This can be due to the ambient temperature changing, heating from the tungsten-halogen lamp, heat from the subject (such as in measuring a monitor), heat from the operator's hand, heat produced in the electronics by repeated usage, etc. For this reason, the i1Pro may require periodic recalibration during a lengthy measurement run to allow it to adapt to the newer thermal conditions. As it happens, X-Rite has designed the instrument to minimize some of these heating effects. For instance, the tungsten-halogen lamp is physically separated from the sensor in a different module so the transfer of heat from the lamp to the sensor is minimized. The sensor is also separated from the housing, so heat is not quickly transferred from the operator's hand to the sensor. Another notable item relates to monitor measurement. Depending on the monitor's backlight technology, there can be noticeable heat coming from the monitor. This can transfer to the i1Pro during the measuring process, affecting the sensor's dark noise. To account for this, when measuring a monitor I place the i1Pro onto the monitor during the warming up period, then I calibrate and measure. This also gives the monitor time to equilibrate for more stable and accurate measurements. The final question is probably how long should the i1Pro be allowed to warm up before measuring? I usually use a minimum 15 minute warm-up period before calibrating and making any measurements. If you want to improve your measurements even more, make multiple measurements per specimen and average these measurements for the final result. Noise is reduced by the square root of the number of measurements, so taking 4 measurements and averaging will reduce the noise by 1/2 (9 averaged measurements by 1/3, 16 averaged measurements by 1/4, etc.). Robin Myers Robin Myers Imaging www.rmimaging.com On May 21, 2011, at 9:24 AM, Millers' Photography L.L.C. wrote:

What is considered the Definition of i1 Pro Spectrophotometer "warming up"?

Regards,

David

David B. Miller, Pharm. D., member Millers' Photography L.L.C. 3809 Alabama Street Bellingham, WA 98226 360 739 2826 digitalimaging@dnmillerphoto.com