Is the Iphone flashlight/torch suitable for use with the spectroscope or will it distort the spectral display?
The LEDs in most phones are composite RGB producing three narrowband (discrete) emissions. The spectral response through a gemstone will not provide absorption response in-between the three colors, which may hide or attenuate certain spectral lines of key element signatures.
The link above provides a typical output on the IPhone7 LED flashlamp/flashlight for example.
Cheers!
2 Likes
thanks, and well done repsonse.
broad band light source such as an incandescent bulb with a 5000 Kelvin filter (daylight) would be better. Halogen lights only a little hotter, so still wlll need a filter… actually, those filters make the light look blue, but the sunlight light spectrum has more blue in it than is evident.
Day light LED bulbs are designed to mimic sunlight with a spectral temperature of 5,500 to 6,500 degreees Kelvin, however some of the red end is cut off and longer wavelengths… they are still relatively broad band and should suffice.
Fatma,
I must apologize for the incorrect information I posted earlier.
The LED Flashlight on the phones are not RGB composites. They are typically a white LED but with some attenuation towards the blue and red ends of the spectrum, as seen in the trace spectra (link in my original response). The screen is the composite RGB and is where I misinterpreted the plots. I still hesitate to recommend the flashlight’s use for spectroscope observations because it does not have a strong red band and exhibits a large null towards the blue. There will be some differences between phone models and manufacturers which could affect the observed spectra as well.
@StevenH26783 suggestion of using a halogen or incandescent or natural sunlight would provide a better light source.
Again, I must apologize for the misleading information.
I think you may have looking at the screen spectrum… the LED spectrum still shows a peak at the blue violet end, maximum at green/yellow and tapering off at the red end. LED lights should work in conjunction with a 5,500 degree Kelvin filter. I don’t think that it is physically possible to obtain a flat spectrum across all visible wavelenths even with direct sunlight and filters…alll light sources, even sunlight will still have a skewed distribution of wavelengths. Electric arcs as with welders have a radiation temperature exceeding natural daily light… these sources cannot be used due to the dangerous ultraviolet emission. I don’t know whether spectroscopes, particularly those that are relatively cheap can be calibrated to adjust for the red end cut off…Not that it makes that much of a difference… … all I know about adjusting for spectral power comes from using a 5000K filter on an incandescent. It does flatten the curve by aborbing some of the yellow/red end which incandescents generate in excess compared to the blue/violet end…the resulting light output will be lower as incandescents put out more light at longer wavelengths… a bright bulb (100 watts) will be necessary… I have used these filters remotely in doing color vision testing…the Farnsworth-Munsell 100 color sorting test requires a flat spectrum to sort colors by hue. The resulting light will have a bluish hue, similar to a cool daylight flourescent bulb. However, that color is the color of the sun’s output as seen from outer space.
don’t know whether you recieved my post… so I’m directing it to you again… thanks
Thank you very much, Steven. Much appreciated.
Thank you, Troy. I appreciate it very much.
1 Like
you’re most welcome… you might find better light sources than I can… research it online… google…
I did, thank you. I was reviewing the conversation before replying back to you, when I discovered my error. 
-Cheers!
If anyone has a better idea, please post… I’m not that much of a gem expert, more of a science guy… often theoretical considerations don’t match what’s practical and realistic…however, a 5000K filter does correct for the lower temperature incandescent lights… the spectrum is shifted towards red and yellow, the blue pass filter flattens the midwavelength light radiation… the resulting color will be blueish when looked at, but that’s because the longer wavelengths are being absorbed and not letting the shorter wavelength colors get overhwelmed. The light transmitted is not very bright… 5000 degrees K is about 10,000 degrees F, the temperature of the surface of the sun. These filters are usually plastic ones and should be readily avaialable and fairly cheap, although nothing is cheap anymore these days!
Without derailing this conversation from its gemology roots, there is a potential misconception that should be clarified here.
Agreed, using a 5000K filter will help correct the saturation from the stronger red/yellow of an incandescent source. The same method can be used to help attenuate the strong blue/violet of a fluorescent source by using a 3800K or 4200K filter. But these are primarily applicable in the photography and ambient lighting environments. They attenuate (reduce) the emission density of the stronger spectra.
But this can adversely affect a visual observation through a gemologist spectroscope, which is absorptive versus emission in nature.
A dated but good resource: “The Spectroscope and Gemmology” by Anderson and Payne, 1998
If you can find a copy of the “Handbook of Gem Identification” by R.T. Liddicoat, I highly recommend grabbing it. It is now a very rare gem!
Cheers!
I have to agree that the intensity of ambient light will be strongly reduced by a filiter. having a very bright light source is not possible using a filter and an incandescent… This will adversely affect the absorption spectrum of a stone. Do you know of a better alternative for a light source that gives an even solar spectrum? Every technique has it’s own drawbacks… using prisms give a broad band absorption spectrum that peaks at a single color…there’s over lap… diffraction gratings better peaks but have to be changed for each color band… none of the commercially avaiable spectroscopes use them…more for optical research than practical…
absorption/emisson spectroscopy (eg… Raman) is far more informative but costs far far more…
The most constant and calibrated light source we have is that giant fireball in the sky. It’s only drawbacks are weather patterns and the diurnal cycle. We continue to try and replicate it here on Earth with close proximations, but most of those come with hazards kin to sunburns and fires.
Hand-held flashlights(torch) with an incandescent or halogen bulb are portable and offer a consistent output. The spectra for tungsten / Iodine (Halogen) does not overlay on any of the mineral constituent spectra, so it has minimal interfering effects. Other halogen elements will interfere with gemstone spectra (Chlorine, Fluoride).
This fiber-optic light source is on my wishlist. It has a wide spectral response 420 - 900 nm covering most of the VIS-NIR range. But from here we start going into lab grade equipment.
you are so right about natural sunlight… it’s the standard against which artificial lights are gauged.
Lab equipment is too expensive for the hobbyist and even professionals unless they are doing ID and grading for a living. Eg: portable field use Raman spectrometers and hand held XRF machines start at over 5K, usually around 12K and go up to 20K… both have limitations in that they are not very sensitive to common rock forming elements- aluminum and silicon…Bench models with high precision cost 5 times as much… pretty impractical for anyone other than in industry and academics…
electron microprobe machines cost 500K to 1 million, charges are 55 to 300 dollars per hour…the ultimate machines cost 1 to 6 million dollars and 50 to 100K per year to run… these machines are laser ablation, ion ablation, and scanning EM ablation mass spectrometers… they are the only way to separate out isotopes and have become sensitive enough to count individual atoms…paying for run times on the machines are quoted at 55 to 150 dollars per hour, 2000 to 3000 dollars for a single whole rock analysis… The GIA does have these high dollar equipment and uses them for research and for precision ID of gems and minerals. Costs for run times are similar…the most important uses of these high dollar pieces of equipment are for geochemical research, and beyond the scope of gemology in general.
1 Like