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Note: This is a version of the Ledlyt Manual written to accompany a demo installation on an Olympus GB. It goes into considerable detail, and is provided for 'mining' by those who really do want the facts rather than the blurb. The text has been stripped from the Pagemaker original and converted to HTML manually.

The Ledlyt Manual

Operation of the ledlyt is hopefully intuitive for a microscopist. The control knob varies LED current from 0 to 30 milliamps. For a clear (water or mounting medium) background likely brightness requirements on a binocular microscope are around 5 mA for a 10X objective and around 15 mA for a 40X. The top (matt) face of the diffuser disc you can see before putting the slide on the stage can be anything between half a millimetre and say 15 millimetres below the slide, depending on the visual effect required. This Olympus GB is correctly set, and raising the ledlyt mount until it reaches the stop will not impact the bottom of the slide!.

Changing the height of the ledlyt provides a very smooth variation in depth of field and shadowing contrast. On a typical subject - diatoms (don't ask me for species) the optimum ledlyt height is around four millimetres below the slide. Variations around a millimetre have discernible optical effects.

In common with many microscopes, if you wind the ledlyt mount right down, it will drop off the bottom of the rack and pinion. Do not panic. Put a finger under the mount and push up the rack slide until it contacts the pinion. Rotating the pinion knob will then draw the rack once more into contact. The battery-driven system shown will run at full brightness for 100 hours, but if you want to 'save the whales' please turn off the light at the switch next to the control knob when you have finished.

You are positively welcomed, taking due care, to swap in a favourite objective or eyepiece for the period you are using the microscope. This Olympus may be old, but it earns its keep doing CCD photomicrography with the ledlyt as an ideal illumination.

The Manual puts down all I know about the ledlyt, and there is no need whatsoever to read it. To balance microscopy written by a chemist/engineer/electronics specialist, Barbara Bowles has added a 'biological' section on long-term use of the ledlyt.

Breck Bowles
15.3.01

This copy remains next to the microscope, please. A copy for short-term loan is available.

Manual contents

The sections are, in order:-

Engineering
Basic mechanicals
Materials
Adapting the condenser mount
The illuminator
Electrical safety fundamentals

Practical ledlyt use

General description

Other ledlyts

Concluding note from Barbara Bowles

There is no need to read any section that does not interest.

* * * * * * * *

Engineering

Basic Mechanicals

The ledlyt was designed by considering the shortcomings of many mains lamp/condenser illumination systems. The condenser is replaced by a unit which incorporates full centering, so alignment can be performed without wiggling the innards of the lighting assembly. Inside the condenser adaptor is a centred sleeve, with a top recess for an optical stop and the glass diffuser disc. The illuminator itself contains a very bright white LED, optically centered in a tube and cast in place. The tube is a ground/lapped fit in the centred sleeve. Precision engineering is enforced here, and any tube will fit any centred sleeve, so if you do need to change illuminators one illuminator is slid out, unplugged from the power supply, and the replacement is slid in. Centred illuminators mean no re-centring, and an illuminator change time of about a minute. The height of the illuminator tube inside the centred sleeve may be altered, although this has not been found necessary so far. A martensitic stainless steel ring is locked on the illuminator by a nylon screw, which will not damage the lapped surface, and this lock point can be varied. The mechanical catch required to hold the illuminator up inside the sleeve is done with two tiny magnets inserted into the brass of the centred sleeve. The stainless ring hits these recessed magnets and sticks. It may not be correct any more to compare the feel of the action with a rifle-bolt, but some care has been taken to make sure it snicks into place.

Materials

The centring screws are stainless steel, and the rest of the unit is turned and ground from brass. The brass is unplated, and so will dull with age. There is plenty of precedent for the use of unplated brass on microscope accessories. Grinding/lapping and plating do not go well together, and since each installation contains a custom-made adaptor, sending each adaptor individually out for plating would not only ruin tolerances, it would add a large cost and time burden to each unit. I appreciate much of the appeal of a new microscope is cosmetic, but perhaps this is not the way the World should be.

The solid brass of the ledlyt does weigh more than the condenser it replaces. There were fears that with a well-worn condenser rack and pinion that was starting to go slack, the extra weight would cause the ledlyt to slowly drop under gravity. A Wild M20 we use has a slack condenser rack, but no gravity slippage has been observed with the ledlyt in use. The Wild condenser is of course pretty solid anyway, so the weight increase has been relatively small.

Adapting the condenser mount

From a pre-war Watson (London) to the Wild M20, the normal mounting for the condenser has been a close-fitting ring around the condenser, often with sprung 'fingers' incorporated into the ring to provide that feeling of 'class' that we all like so much. All that is required is to measure the condenser diameter, height, and one or two other dimensions, with a precision vernier calliper, and have a corresponding brass adaptor made. The holding screw is loosened, the condenser smoothly pulled out, and the adaptor smoothly pushed in. Adapting the Olympus and the Wild produced no problems at all, and doing the same to the Watson looks equally trouble-free.

A binocular student Nikon we own has a fork-mount, and the corresponding condenser is a lightweight alloy unit. There are angled bevels on the condenser that would have to be replicated on the adaptor, making measurement harder, and adaptor machining more expensive. Fork-mounts may have become more common. We have not fitted a ledlyt to this Nikon, mainly on the basis it was plainly necessary to also replace the XY stage, the focusing arrangements and the entire optics before adequate performance could be achieved. The Olympus GB is in a different class to the Nikon. The optics work, the focus works, and the XY stage is exemplary.

The illuminator

Over the last two years very high brightness LEDs have appeared. Light outputs are still rising every few months, but the main breakthrough seems to be over. A bright LED has risen in peak output from 100 millicandelas to 8000 millicandelas, and of course white LEDs have appeared for the first time.

The white LED is basically a high brightness blue emitter. InGaN (Indium Gallium Nitride) creates an intense almost-monochromatic blue. The light-emitting junction is covered with a YAG (Yttrium Aluminium Garnet) phosphor which fluoresces green and some red to produce an effect similar to a solid-state fluorescent light. The maximum recommended setting for cool running is a current of about 30 milliamps, and this is what the ledlyt power supply delivers on setting 10.

When the illuminator is removed from the centred sleeve, you are advised not to stare at the LED running at full brightness. Eye damage is not likely, but possible. It is perfectly obvious from the brightness of the point source that it should not be stared at. During the making of the ledlyt the concentrating lens-end of the LED is ground off. This spreads the radiance pattern, leaving the only danger the prospect of the tiny unmagnified junction point-spotting on the retina. When the ledlyt is assembled, the light source is as safe as any other.

Electrical safety fundamentals

Electrical safety regulations are as praiseworthy as those in the airline industry. They are essential, and drawn up by a team of inspired pessimists. Even if implementation is lax, flouting the safety regs is a dangerous business.

A base-illuminated microscope is a metal box containing either a mains-voltage lamp or a step-down transformer plus a low-voltage quartz-iodine lamp. Often the transformer is in a separate dimmer box. Normally all boxes are earthed to the mains earth, so that if mains appears on any metal case it shorts to earth, blowing a fuse and restoring a safe, if non-operating, condition. The alternative approach is exemplified in a modern cheap quartz-iodine desk lamp. An isolation transformer is used with very generous and pessimistic insulation between the mains winding and the low-voltage secondary winding, to make the transfer of mains direct to the secondary winding as close to impossible as fate will permit. Such a lamp may have exposed metal parts and still meet safety regs. Similar transformers are used in 'battery eliminators' to allow battery- powered devices to be safely used from the mains, and also in small hi-fi gear that cannot be grounded, but has to come in a metal box. These transformers also contain thermal overload fuses, are described as 'double insulated', and are sold in Australia, made overseas to Australian safety specs.

A microscope is all-metal, and in personal contact. Inside the ledlyt illuminator is significant insulation to prevent either side of the four volt DC supply from reaching the condenser adaptor and hence the metalwork of the microscope. We take the approach used by any small operation of not supplying a mains transformer and wiring, but instead making the product accept 6 to 12 volts AC or DC, and advising our customers to buy a double-insulated power pack to supply this, meeting Australian safety regs. There are none on sale openly that do not.

The sledgehammer approach to safety is to run the ledlyt as demonstrated with a 6 volt battery power supply. With the batteries at around three dollars each, and lasting 100 hours at full brightness, a case can be made, at three cents per hour, for doing away with the mains connection entirely. Short of eating the battery, this removes the risk of personal harm, and exemptions apply for low- voltage battery-driven apparatus in all kinds of electrical safety regulations.

Practical ledlyt use

Before reading on, the reader is reminded of an old story by Hans Christian Andersen entitled 'The King's New Clothes' covering the sale to the King of an illusory set of clothes, described with such magnificence that no-one, King included, wanted to admit they could not see them. If you cannot see the described ledlyt features down the microscope, then they do not exist.

General description

The field under objectives 10X to 63X is uniform, and a very neutral grey-white indeed. The light can be run right down to extinction without a colour shift. The overall impression is of an outstanding lack of any colour, until you notice there are small coloured areas in many of the cells viewed, standing out more prominently than usual, against the monochrome. Almost everything appears sharper, perhaps unnaturally so. With the ledlyt just under the slide, the picture resembles a wide-open condenser field, with very flat illumination, and no shadowing inside cell structure. As you lower the ledlyt farther from the slide, cell shadowing and depth of field steadily increase.

The easiest effect to identify is the edge sharpening. Operating against a dull grey background, you will notice as you focus on a cell edge that at the critical point a very thin white line, brighter than the background, runs along the cell edge. The extra sharpness this creates may be illusory in fact, but who's counting? This effect has been optimised in the ledlyt as presented. It has some similarities to phase contrast, and is a function of the distance of the light source, the diameter of the stop, and the amount of diffusion in the glass disc. This effect has been researched and produced empirically - if you can explain the theory you are at least one up on the inventor.

The general achromatism is simply the missing condenser. In primary school terms, once you have bent the light, you never get it straight again ... Against the lack of introduced tints from the condenser, the actual coloured areas stand out more prominently.

The depth of field shift appears to be the effect of moving a semi-diffused illuminator from close, where almost all light is scattered, to distant, where it begins to approximate a point source.

Barbara Bowles has developed a technique where algae etc are counted by stranding them on a fine nylon silk-screen printing mesh used as a filter. Using normal condenser illumination the nylon of the mesh contains all sorts of colour and depth effects that nake it hard to pick out the stranded organisms. Under ledlyt illumination pretty close to the slide, the mesh reduces to monochrome 'wallpaper' and its inhabitants are much more clearly seen.

Other ledlyts

Until the system was optimised, a blue ledlyt plainly showed more surface-marking and fine-spine detail than the white unit. Barbara Bowles says diatom frustules were being viewed. Blue is shorter wavelength, so the resolution has risen. As the colour and edge enhancement was optimised, the blue became less impressive since fine colour rendition was making other detail visible. There may still be specimens which would benefit from a blue light source that can be quickly plugged-in. Notable under blue illumination was the start of Newton's Rings if a binocular was being used. The monocular is relatively immune, indicating that the standard binocular beam- splitter is not such an invisible asset as is often thought.

I think that is sufficient uninformed comment. I will hand over to Barbara Bowles PhD

NOTE FROM BARBARA BOWLES

For many years I have used a Wild M20 microscope with a special optical base which was designed, amongst other things, for fluorescence work. It took up a great deal of valuable space and was heavy and cumbersome to align (mainly because it was much longer than my arm length). I was delighted when the Ledlyt was being invented because it provided a very good way out of several problems. Unfortunately for Breck Bowles, I have developed over the years (as many microscopists do) a critical eye for optics, based, I may say, on practical use, as my knowledge of the physics is fairly rudimentary. The result was that I nagged until I felt the Ledlyt was producing the sort of image that I would like to work with. I hope it is also the best image, but tastes in optics differ.

I have now been using the Ledlyt system for about four months. It has been free from problems and made my life as a microscopist much easier. I have noticed more clarity on the edges of surfaces, and generally better detail within cells in the algae I observe. The effect is a little like phase contrast, which produces very clear edges, and therefore it is also good for seeing flagellae and other fine objects, which tend to disappear with the more usual illumination system. I usually use a magnification range of 100X to 400X and occasionally oil immersion at 700X to 1000X. So far I have had no occasion to use oil immersion with this illumination system, but I see no reason why it should not perform well.

There is only one problem with using this system for student microscopes. It is much too easy to set up, and the students will never have to learn about the operation of that most challenging of microscope parts, the condenser system.