Don't know if this fits cuz I'm NOT afraid to ask....

[wmodavis]

Likely this is a simple one to answer so here goes from a relative newcomer to this sport...

As I'm interested in getting a microscope and am fascinated by some of the contrast enhancement techniques. Here's my question about using a LED light source with a polarizing filter. Are they compatible? Anyone have any knowledge and/or experience using them together? Any known or expected enhancement or degradation of the contrast enhancement when combined?

The scope I'm thinking of and many out there now days tout and use the LED lighting and I've seen a number of add-on/DIY polarizing kits I assume they are compatible but just want to get it clear by hearing from experts here. In my reading I have not yet come across any article/blog/opinion dealing with this. By that indication likely there is no problem with that dynamic duo but have to ask.

Thanks for input.
Bill

[75RR]

Here's my question about using a LED light source with a polarizing filter. Are they compatible?

They should be, don't know of any compatibility problem nor any reason why there could be.

The scope I'm thinking of and many out there now days tout and use the LED lighting and I've seen a number of add-on/DIY polarizing kits I assume they are compatible ...

I would not focus too much on LED lighting, it is not critical, in fact there is a lot to be said for original factory designed lighting.
If it ain't broke don't fix it!
As you have seen, some members have switched to LED, so if you decide at some point to go over to the "Dark Side" you can always do so. ;)
Much more important is the microscope build quality and upgradability. Your best option is a second hand 160 system (finite) from one of the major manufactures from the 1980s. Have an especially good look at American Optical

Have a look at this thread for a DIY Polarizing solution: viewtopic.php?f=25&t=1725&hilit=polarizer

[gekko]

Bill, I may be nitpicking here, but I thought I'd add a comment that strictly, polarization is not a contrast enhancing technique. It does show many objects in a different "light" if they contain birefringent material, and since it is very easy and inexpensive to implement on any microscope, it is well worth doing. I think contrast enhancing techniques are things like oblique illumination and its many variants, Rheinberg illumination, phase contrast, DIC, and darkfield.

[apochronaut]

There was a time, when I thought of led as a logical choice to improve the illumination of certain microscopes but in the end, they are all models that have something wrong with their illumination system, or they have an inadequate illumination system for the purpose I have in mind. I echo 75RR's comments that there is a lot to be said for factory design lighting. Concerns about power usage in microscopy, are not the mega factor that they are in broad based domestic or industrial lighting scenarios. The world is hardly going to be saved by the society of microscopists with an environmental conscience. Led is a harsh lighting but has the advantage of shedding a diffuse beam, whereas filament lamps shed a focused beam. Diffuse beams are easier for novices to use, because they are there, like the sun. Focused beams need to be correctly aligned and properly regulated, so take a little skill and a properly working system.
There is a current obsession with kohler illumination. Kohler illumination was a by-product of the invention of the filament bulb. A large gas flame, the illumination method of choice prior to the late 19th century, can be critically focused, or slightly de-focused and provide a perfectly even illumination , whereas a filament cannot be. De-focusing the illumination source turned out to mimic a gas flame well enough, so kohler illumination was born. A gas flame is the result of a dispersed combustant, a kohler modified light beam is the result of a dispersed image of a compact combustant. The two do the same thing. Led's provide light more like the former, so have a degree of incompatibility with the lens systems engineered to provide kohler illumination. They are also highly over rated in their resultant intensity, relative to tungsten or halogen bulbs. They also produce far too much short wavelength light and may be damaging to the eyes.

[wmodavis]

It is satisfying and more than that helpful to get in depth responses to my posts here from some of you guys I've red a lot of. I always learn new things to go search out and learn even more about. Good stuff on the LED issue or non issue as the case may be. One of my reasons to question is because a microscope I'm seriously considering seems to come that way & didn't want to find out the negatives after I bought.

In reading advertisements (dangerous in isolation) it seemed to me that LED was/is the up and coming, better than anything solution though now seeing it as a solution to a non-problem.

In my early career as an electronics design engineer we were told to 'design in a FET'. Because the FET was the new rage at that time in ancient history and it helped sell the consumer item cuz "It had a FET in it" whether or not the FET really helped or resulted in better performance. Kind of like an old blender I have that advertises in BOLD print that it is "solid state". Actually it has one diode. There are many parallels in life.

And gecko thanks for differentiating the polerizers from contrast enhancing. I think? I knew that from my reading but you definitely clarified it.

And personally guys, I like long, detailed, technical answers. I may not understand it all but what a way to learn. Thanks.

[gekko]

I would like to agree with 75RR and apochronaut about not converting (at least initially, until you are driven to do it for some reason) tungsten filament illumination to LED. I don't know that I would shun an instrument that was originally made with LED illumination, as the designer would have presumably optimized it for LED. LED has both advantages and disadvantages. Advantages include much longer life, and much cooler operation, so your slide typically remains significantly cooler than with a halogen source, especially where the lamp is in the base of the microscope. Disadvantages include, as apochronaut noted, increased emission in the short end of the spectrum, although as technology changes this may not be a big issue and can be ameliorated with a long pass filter, but also, depending on the intended use, its spectrum, which differs from tungsten, may alter colors subtly but significantly if color is important (for example in petrology where the type of rock needs to be identified using a polarizing microscope).

[wmodavis]

Have gone back and read some on LED lighting including ads from vendors. A couple things stuck out to me. Most talk is about cooler temperature, long life, low power etc. Nothing about its characteristics that might aid or distract from quality of viewing in microscopy. So it begs of sales puffery. More has been said here in this thread about LEDs being good or bad for actual viewing.
Apochronaut - you mentioned the shorter wavelength. Wouldn't that be better for resolution sake? I was thinking of experimenting with blue LEDs for resolution. Any possible validity to that thinking? Of course if it blinds you you'd have to switch to a Braille model scope. And Apochronaut shed more light on the diffused/focused light effect and what the end effect of that is. I'm not really focused on LED lighting it's just that it seems to be very common on new microscopes.

Much appreciate the helpful discussion to help steer me in a productive direction.

[75RR]

Here is a link to some more basics.
The link takes you directly to the illumination chapter, but I would suggest that you read all the chapters.

http://www.microscopy-uk.org.uk/index.h ... llumin.htm

[wmodavis]

Thanks 75RR. I've seen that before but will give it a thorough study now that you provided a link. Better bookmark it for future referral too.

[billbillt]

I have built several LED devices for some of my stands and have had good luck with them.... I feel that it pays to experiment with different types of lighting.. This is part of the fun!... LED lighting must be useful, most of the major makers offer stands with LED lighting... It works well for me.. I take some of the fears of LED as nothing more than an old fashioned resistance to change..

BillT

[billbillt]

The wonderful videos posted on this forum by Bill Porter are taken with a Nikon stand that he converted to LED... It would be hard to fault the lighting in his videos..

BillT

[Dale]

A solid state blender, right up there with HD toothpaste.
Xenon bulbs do not emit UV radiation, but do not exist in 6 volt.
Please excuse my syntax, tonights wine was really good.
Dale

[mrsonchus]

I don't know much about it but the 5W 12V LED 'bulb' I use explicityly states zero UV, if that's any help. Please excuse my ignorance of this subject.

[apochronaut]

In the current study, the researchers wanted to accurately simulate exposure to indoor lighting, says corresponding author Chang-Ho Yang, a professor and ophthalmologist at National Taiwan University’s College of Medicine. He points out that earlier work shone light directly into the eyes of experimental animals, which may induce damage but hardly corresponds to the indirect way in which most people are exposed to artificial lighting.

“We created an exposure environment where rats could run freely in a cage with the light source set on the rack ceiling twenty centimeters above the cage roof,” Yang explains. “This mimics the ‘domestic lighting’ condition as much as possible, which should greatly reduce the injury—theoretically.”

However, the retinas of rats exposed to either blue or cool white9 LED light showed evidence of retinal damage and cell death after 9 days of exposure. Although rats exposed to cool or warm white10 CFL lights also showed some evidence of damage relative to unexposed controls, in general differences were much less pronounced than those observed in the LED-exposed rats. The authors suggest the observed injuries may have been a consequence of oxidative stress from reactive oxygen species that were generated in retinal tissue.3

The rats used in these experiments were albino, and their unpigmented eyes were more sensitive to all effects of light. But even in typically pigmented eyes, Yang says, neuronal cells are incapable of repairing themselves or regenerating after damage. This makes it important to pin down mechanisms of injury and link them with clinical studies matching the conditions under which people will ultimately be using LED lighting. Future studies may suggest a spectrum threshold that could help the lighting industry optimize eye-friendly products, he notes.




The above is just a quote from, I believe, an opthalmology journal . They are not talking about UV here. They are talking about led lights that are preponderantly short wavelength blue light.

[billbillt]

Yes, non UV emitting LEDs are very common.. The exclusive use of them would cancel the fear of UV damage... The are very inexpensive and provide a cool and reliable alternative to halogen lighting..

[billbillt]

Also, inexpensive UV filters can be placed over the LED light source to allay the fears of LED UV emission... An easy fix...

[wmodavis]

LEDs are very monochromatic light so there is not much of the light spectrum present. Although the white LEDs must be broader spectrum content.

[mrsonchus]

LEDs are very monochromatic light so there is not much of the light spectrum present. Although the white LEDs must be broader spectrum content.

Oh, sorry, I don't quite understand old chap?

[75RR]

inexpensive UV filters

And there is the rub ...
inexpensive UV filters, inexpensive LEDs etc ... there is an awful lot of no name / no brand junk out there, in which whatever it says on the package is not worth the plastic it is printed on.

If you are going to go for a home made LED setup † make sure you obtain your LED from a reputable manufacture.
A reputable manufacturer provides documentation on each of the LEDs they make and perhaps more importantly have something to lose.
By which I mean reputation = money, as in market share.
The fact that it is at least theoretically possible to sue them is also relevant.

Cree is not the only reputable LED manufacturer, just the only one whose products I have used.
See pdf:
http://www.cree.com/~/media/Files/Cree/ ... ampXML.pdf

Two things:
1) LED safety tests that say "don't worry" tend to refer to ambient light, sometimes to computer screens/tablets
2) LED saftey tests that say "worry" like the Madrid study ‡ "tested someone looking at the equivalent of a 100watt light bulb, at a distance of 12 inches for 12 hours a day," he says. ‘And this isn’t something a normal person would be doing.’
Sound familiar?

† Ebay conversion kits that do not come with documentation (or someway to verify the LED used) should also be considered suspect.
‡Dr. Celia Sànchez-Ramos of Madrid’s Complutense University (unable to find direct link)

[billbillt]

All of this reduces to common sense... The whole point of this is not to let what a person says deter you from experimenting with LED lighting... Ample evidence can be found pro and con about the dangers of the "DREADED" UV emission... LED components are so inexpensive a person can spend ample time developing a system that works for THEM..

[75RR]

2) LED saftey tests that say "worry" like the Madrid study ‡ "tested someone looking at the equivalent of a 100watt light bulb, at a distance of 12 inches for 12 hours a day," he says. ‘And this isn’t something a normal person would be doing.’
Sound familiar?

Just in case it was not clear: looking at the equivalent of a 100watt light bulb, at a distance of 12 inches for 12 hours a day (change the wattage and the hours) and it is pretty much exactly what we do.

[wmodavis]

Darn! I wrote a tome and it disappeared. Maybe I'll redo.

But I'll try a diagram if I can make it work.

http://www.rohm.com/web/global/led-ligh ... cture/led2

Particularly I'm referring to Topic 10: What is the light emission spectrum?
Hope the link comes through.

[billbillt]

Hi Davis,
Thanks for the link... What was interesting to note for me was the graph in topic 10 shows almost zero emissions in the UV spectrum... As I posted, there are pros and cons, everyone has their own opinion... What is important is to experiment... Find a method that works for you.. An LED conversion is surely a doable option...

[billporter1456]

Interesting thread! Thanks to all who have contributed to it.

While I don't know whether staring through my eyepieces for hours at protists illuminated by my LED setup (Cree 3w XT-E) is damaging my eyes, I have started to significantly reduce observations through the eyepieces in favor of looking at my computer monitor. I always have an Amscope MU300 USB camera in the trinocular tube so it's a simple mater of firing up the camera software when I have a slide to look at. Sometimes I go ahead and start recording a video without any idea of whether I will come across anything interesting. I can always delete the video file if there was nothing of value in it. Just my $.02 contribution to a nice thread.

[Peter]

While I don't know whether staring through my eyepieces for hours at protists illuminated by my LED setup (Cree 3w XT-E) is damaging my eyes, I have started to significantly reduce observations through the eyepieces in favor of looking at my computer monitor.

Hi Bill,
Your computer monitor is probably LED also.
Peter.

[billporter1456]

While I don't know whether staring through my eyepieces for hours at protists illuminated by my LED setup (Cree 3w XT-E) is damaging my eyes, I have started to significantly reduce observations through the eyepieces in favor of looking at my computer monitor.

Hi Bill,
Your computer monitor is probably LED also.
Peter.

Hi Peter,

I can't argue with your logic on this one. Somehow it feels safer.

[billbillt]

For me, decreased vision comes from getting old...

BillT