Hi Sarah, This is an excellent question. I don't know the answer. The Minolta Chromameter CR 200 I was using is almost portable (9kg including the rigid cover). It will be good if there were lighter ones that are reliable.

Thanks, Aurelie. Actually, my desktop Avantes AvaSpec and AvaLight weigh considerably less than that - the difficulty with the kit is the optic fibres and the fragility of the bulb in the light source, meaning that heavy handling can damage the kit, and the need for a mains power source for the light makes accurate use in the field very challenging.

Looking at the manual for the Minolta Chromameter, it doesn't seem to measure UV (important for anything involving insects!) and only outputs as RGB or other simplified outputs, not a fully comprehensive reflectance spectrum? Looks good for industrial QA but less good for insect sensory ecology modelling. What I'd really love is something the size of a water pistol with a 2mm wide recording probe mounted at 45 degrees, that could be pointed at a surface (flower, fruit, dead bee, etc.) and would give an instant, accurate diffuse reflectance spectrum 300-700nm in 1nm increments - but I am not sure the technology has reached that point just yet!

Dear Sarah,

we're using a jaz from oceanoptics with good success. However, independent od the machine, I have problems with the 45° angle and with the black and white standards, since in many flowers the reflectance is strongly dependant of the angle and microtexture properties of the petals have impact on the measurements, which you can't compensate with any black or white standard. For example we found many white hummingbird-pollinated flowers reflect not more than 25% of the light, which should result in a dark grey colour (Lunau K, Papiorek S, Eltz T, Sazima M (2011) Avoidance of achromatic colours by bees provides a private niche for hummingbirds. J. Exp. Biol. 214: 1607-1612). Nowadays we measure reflectance at different angles and are thinking about other standards for calibration.

Klaus

Dear Klaus,

Wow, the Jaz looks fascinating. I'd love a chance to try that out at some point!

That's a good point for natural stimuli like flowers, especially in light of iridescence work by Whitney, Glover, etc. Would be interested to receive updates if new calibration standards are developed - please publish whatever the evidence suggests is good!

Sarah

Hi,

It is possible to achieve reasonable accuracy using photo's that are calibrated a posteriori using an included color chart. This has the advantage of being able to measure any region in the image, i.e. not being limited to the SPM aperture. Downside is lower accuracy, say 0.3 dE*2000 average, 1.6 dE*2000 99th percentile and a maximum below 3.6 dE*2000. This is image measured colors versus SPM values. Note that this is with a very good chart, if the chart has some tolerances the error obviously goes up. We use this for medical and forensic imaging and measurements.

Well I would say if you compare an old desktop version to a new handheld you might find comparable results. But comparing new equipment the difference will still be there. Handheld instruments generally has to sacrifice stability and accuracy to reduce size and weight. Knowing the error tolerance in your experiments is therefor important.  Try to send the vendor a test spectrum and ask them if they can give you the uncertainty on a key parameter if it had been measured with their instrument. If they can't give you that - they might not know what they are doing.

Anders

Dear Yves,

Thanks for this. I am not familiar with SPM as a method of colour measurement. I agree using a known, quantified stimulus to compare is a good idea - for me as an entomologist, it has to be something with predetermined UV reflectance too. Knowing the absolute reflectance of the stimulus, independent of lighting/background is key for then modelling the appearance to an insect under different conditions.

Dear Anders,

This is a good idea. If I or my colleagues will be going shopping for a new machine any time soon I will certainly try this!

Sarah

Hi Sarah,

Because you mentioned colour in your initial question  I assumed you were interested in colour measurements (tristimulus values like CIE XYZ), not full spectra. Such measurements are often performed with a spectrophotometer with appropriate 'color matching functions' to mimic human vision. The cheaper way is to use a colorimeter which uses just three sensors too obtain tristimulus values directly. These devices are cheaper, often less precise and they are limited in their capabilities because they cannot decorrelate the impact of the built-in light source. Anyway, long story short: my suggestions may not be appropriate for your use-case. Good luck.