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Here, we introduce the light and illumination methods that are convenient for observing cylindrical transparent objects made of materials such as resin.

1. Coaxial light alone

When the magnification is very high, the observation will effectively be of a flat surface, allowing for observation with coaxial light alone in some cases.

2. Twin Arm light (from the longitudinal direction)

Illuminate from a low angle along the longitudinal direction of the cylinder.

The brightness is uniform, resulting in an easy-to-observe image.

3. Twin Arm light (from the lateral direction)

Illuminate from a low angle along the lateral direction of the cylinder.

Surface scratches can be clearly observed as well.

The “coaxial light” and “Twin Arm light” used in this case are also available from our company.

High-performance LED lighting for coaxial units (3W) LED-3WLTS

Twin Arm light

Our large-diameter ring light can be mounted at a distance of approximately 30 to 40 cm to illuminate an A4-sized area relatively evenly.

However, this is the practical limit for this level of illumination.

To evenly illuminate areas larger than A4 size, a large lighting system, such as the one shown below, may be necessary.

The following is equipment from LPL (photography equipment manufacturer).

Another method is to attach a surface-emitting light as shown below.

For a simpler solution, you can arrange a desk light-style fluorescent lamp as shown above to achieve broad-area illumination.

(Fluorescent lamps diffuse light more than LEDs, having lower directivity.)

When performing dimension measurement using transmitted light, the appearance can vary depending on the “type of transmitted light” and the “brightness” used.

This article introduces the “recommended light” and “brightness” for dimension measurement using transmitted light, so please be sure to read it through to the end.

・Use “parallel transmitted light”

There are several types of transmitted light devices.

　・Diffused transmitted light (general type of transmitted light)

　・Parallel transmitted light (compact transmitted light suitable for dimension measurement)

　・Telecentric light (high-precision, large-scale light used in projectors and similar devices)

Of course, telecentric light is the most suitable for dimension measurement.

However, it is large in size and comes with a significantly higher cost (it is integrated into high-precision projectors and dimension measuring instruments).

For general use, we recommend parallel transmitted light.

The lighting method becomes particularly important when measuring samples with significant thickness.

(For thin samples, the difference is less noticeable.)

We measured the Mitutoyo block gauge with a width of 9 mm.

＜Diffused transmitted light＞		＜Parallel transmitted light＞

* Each was measured twice consecutively.

For items such as glass scales, either lighting method is suitable.

However, when the specimen has thickness, we recommend parallel transmitted light.

・Adjust the brightness to a “darker” setting

Generally, adjust to a “darker” setting.

Increasing the illuminance causes the white areas (bright spots) to expand.

We measured a glass scale with a radius of 2.5 mm using our non-calibrated microscope.

(When the measured area is white, increasing the brightness causes it to appear larger.)
* To eliminate variation due to the operator, the “Edge Automatic Detection Mode (A)” was set.

＜When adjusted to a brighter setting＞   ＜When adjusted to a darker setting＞   ⇓ Zoom in on the area within the red frame above   ⇓ Zoom in on the area within the red frame above

With our non-calibrated microscope, it is recommended to adjust to a slightly darker setting, within the range where the automatic edge detection mode (A) functions stably.

Dimension measurement (auto-calibration) microscope (medium magnification) CT200HD

Dimension measurement (auto-calibration) microscope (high magnification) CT200HD-H

When performing dimension measurement using transmitted light, the appearance can vary depending on the “type of transmitted light” and the “brightness” used.

This article introduces the “recommended lighting” and “brightness” for dimension measurement using transmitted light, so please read it through to the end.

・Use “parallel transmitted light”

There are several types of transmitted lighting devices.

　・Diffused transmitted light (general type of transmitted light)

　・Parallel transmitted light (compact transmitted light suitable for dimension measurement)

　・Telecentric light (high-precision, large-scale light used in projectors and similar devices)

Of course, telecentric light is the most suitable for dimension measurement.

However, it is large in size and significantly more expensive (it is integrated into high-precision projectors and dimension measuring instruments).

For general use, we recommend parallel transmitted light.

The lighting method is particularly important when measuring samples with significant thickness.

(For thin samples, the difference is less noticeable.)

We measured the Mitutoyo block gauge with a width of 9 mm.

＜Diffused transmitted light＞		＜Parallel transmitted light＞

＊Each was measured twice consecutively.

For items such as glass scales, either lighting method is suitable.

However, when the specimen has thickness, we recommend parallel transmitted light.

・Adjust the brightness to a “darker” setting

Generally, adjust to a “darker” setting.

Increasing the illuminance causes the white areas (bright spots) to expand.

I measured a glass scale with a radius of 2.5 mm using our non-calibrated microscope.

(When the measured area is white, increasing the brightness causes it to appear larger.)
* The “Edge automatic detection mode (A)” was set to eliminate variation due to the operator.

＜When adjusted to a brighter setting＞   ＜When adjusted to a darker setting ＞   ⇓ Zoom in on the area within the red frame above   ⇓ Zoom in on the area within the red frame above

With our non-calibrated microscope, it is recommended to adjust to a slightly darker setting, within the range where the automatic edge detection mode (A) functions stably.

Dimension measurement (auto-calibration) microscope (medium magnification) CT200HD

Dimension measurement (auto-calibration) microscope (high magnification) CT200HD-H

Typically, when magnifying and observing cylindrical shapes with small diameters and high reflectivity (such as wires and filaments), glare may occur, making observation difficult.

This time, various methods of illumination were applied under the following conditions for observation.

(1) Observation with the standard LED ring light

The standard ring light causes reflection (glare) to occur.

(2) Illumination from a low angle along the longitudinal direction of the specimen

(3) Arch light

■ Advanced application

An alternative method is to use the “4-segment LED light” and “V-block” for observation.

＜4 segment LED ring light＞

Illuminate two diagonal points and shine light from the longitudinal direction of the specimen, as shown in (2).

(This alone may be sufficient to achieve the desired effect)

＜V-block＞

Attach a reflector (in this case, white paper) to the V-block to allow the light to wrap around the specimen.

The “LED ring light”, “twin arm light”, and “arch-shaped light” used above are available from our company.

Ring light

Twin arm light

Arch-shaped light LV-AR series arch light

The appearance of concave surfaces can vary depending on the shape and depth.

We observed relatively large concave shapes using various methods for comparison.

The samples are as follows:

1. USB memory connector section

2. Small engine part, φ5mm, with a screw in the 15mm deep section

3. Mechanical pencil lead holder section, φ5mm, with a depth of 6mm

Observation using a standard high-definition microscope TG200HD2 (25 ~ 150x)
1. USB memory 2mm x 10mm, depth 8mm
(30x)	(120x)
Even with a standard microscope, increasing the illumination to its maximum allows for relatively clear observation.
2. Small engine part, φ5mm, with a screw in the 15mm deep section
	Since the depth is 15mm, the light from a standard ring light has difficulty reaching the bottom, making observation challenging.
(80x)
3. Mechanical pencil lead holder section, φ5mm, with a depth of 6mm
(30x)	(120x)
Increasing the magnification causes the image to become slightly darker.
Changing the front ring light of the TG200HD2 to a smaller diameter (LED-16) version   By using a smaller diameter, the illumination angle becomes shallower, allowing the light to reach more easily.
1. USB memory
2. Small engine part
3. Mechanical pencil lead holder section
Changing the lens to a borescope (rod lens)
The borescope (rod lens) is available in sizes of φ4.0mm and φ2.7mm.

IC prints are often made in gray or other colors on the black molded surface, making them difficult to read even when magnified under standard lighting.

■ Standard ring light

■ Dome light (indirect light)

Dome light

■ Polarized observation (inserting polarizing filters at the lens tip and ring light)

Microscope halation removal set GR-HL

For the light-emitting side, we will install the polarizing filter attachment unit that we manufactured.

For the light-incidence side, we will use the MIDOPT polarizing filter, which is installed inside the C-mount.

(It will be mounted inside the camera, as shown below.)

The filter on the light-emitting side is adjustable, allowing for polarization observation with this setup.

Glossy convex surfaces can cause reflections when observed with the ring light, which is standard equipment on our microscopes, making observation difficult.

■ Light

When using a standard ring light, the impact of reflections becomes more significant.	Attaching a polarizing filter to the lens tip and the light side when using ring light can improve the reflections to some extent.
Using twin-arm light can further reduce reflections, as shown in the photo below. (Angle adjustments and other settings are necessary)	Simply adding a polarizing filter to the lens alone can further improve the results, as shown in the photo below.
Observation of a convex lens (object) using the same method (ring light → low-angle twin-arm light).
(Note) For lenses, since the lens itself is transparent, the background color becomes important. In the above example, the background is white, and the lens is not placed directly on the surface but is slightly elevated for observation.

When detecting metal body steps, scratches, dust or foreign particles on transparent surfaces, and dust or foreign particles on mirror-like surfaces using standard light, reflections, and ghosting can occur, making observation difficult.

One method is dark field observation. (For more details, please refer to “What is dark field observation?”)

By setting the background to black and using low-angle LED light, a simple form of dark field observation can be achieved.

If there are steps or scratches on the metal, those areas will appear white under illumination.

Dust and foreign particles on transparent surfaces (lenses) will also appear white under illumination.

Dust on mirror-like surfaces (silicon wafers) will also appear white under illumination.

	Low-angle LED ring light GR56-N
	Low-angle bar LED light (Customized product requested by the customer)

The closer the spherical shape is to a mirror-like surface, the more difficult it becomes to observe. A sphere contains various radii, and the closer it is to a spherical body, the more likely some areas will experience halation, making it impossible to see clearly.

We scratched the mirror-like spherical surface and conducted a comparative observation.

1. When using the halation suppression function (HDR) of a high-definition microscope

We observed the spherical metal using a high-definition microscope.
＜Before halation suppression＞	＜After halation suppression＞

2. When using dome-type light

＜When using a 56-LED ring light＞ Halation occurs with simple reflected light.	＜When using dome-type light＞ By providing uniform illumination to the spherical metal, halation was significantly suppressed.

	Dome light DC-170W
	It is also compatible with our microscopes.

※ When using dome-type lighting in combination with the halation suppression function of a high-definition microscope.

Dome-type light + Without halation suppression function	Dome-type light +With halation suppression function

Using dome-type light and the halation suppression function of the high-definition microscope resulted in a significantly clearer image.

For more details, please get in touch with our technical support.

Coaxial light is designed specifically for “glossy flat surfaces.”

■ Glossy flat surfaces (suitable for coaxial light)

For example, with objects like the ones below, the resulting image would appear as shown on the right.

The caliper also appears as shown on the right.

■ Glossy surfaces with irregularities or curves (not suitable for coaxial light)

Driver

The image will show only the top of the curve (R) illuminated.

Drill bit

The image will show only the edge illuminated.

■ Non-glossy (diffusely reflective) flat surfaces (not suitable for coaxial light)

Paper (printed material)

Using coaxial light results in a dull image. When observing printed material with a “ring light”, the image appears clear, as shown on the right.

When using our high-magnification lens (SDS-Z) without the auxiliary lens, it is possible to use both coaxial light and ring light simultaneously.

The high-magnification lens (SDS-Z) comes standard with a 1.5x auxiliary lens.

In this case, the working distance is 52 mm.

Due to interference with the coaxial light unit, the ring light can only be mounted at the tip of the lens.

Therefore, in this case, only about 20 mm of working distance can be achieved from the lens tip.

Due to the ring light being too close to the object, a light hollow effect (※) occurs.

(It is not practical in terms of both illuminance and working distance.)

※Hollow effect: When the ring light is too close to the object, the center becomes dark.

When the auxiliary lens is removed, the working distance becomes 95 mm.

Additionally, an LED mounting ring can be attached to the area where the auxiliary lens was removed.

Even when the LED ring light is attached to the tip of the lens, a working distance of approximately 60 mm can be maintained.

However, since the LED mounting ring is attached to the lens tip, the auxiliary lens cannot be installed, so the magnification cannot be changed.

(When using a high-definition camera, the magnification ranges from 55x to 320x. ※Calculated value based on a 17-inch monitor.)

Of course, if the coaxial illumination is not used and the ring light is attached to the body of the lens, the auxiliary lens can be used. (See the picture below)

Even with a coaxial illumination lens, if the light guide port is removed, a ring light can be attached.

If you prefer to switch between coaxial light and ring light instead of using them simultaneously, choosing a coaxial illumination lens allows you to switch between the two as needed.

Coaxial illumination is primarily used for observing objects with high reflectivity and smooth surfaces (plated surfaces, mirror finishes, silicon wafers, etc).

However, by utilizing the characteristic of illumination from a 0-degree angle, coaxial lighting can also be used for observing the interiors of holes in metal parts or inspecting electrodes in gaps.

Comparative image

In coaxial lenses with a half-mirror inside, it is not physically possible to insert a half-mirror larger than the diameter of the lens.

To observe a wide area, one solution is to use a planar light-source coaxial illumination system, separate from the lens, and position it along the optical axis.

The above setup uses a low-magnification lens and a 25×25 mm planar light-source coaxial light.

With this configuration, it is possible to observe the entire surface of a 1-yen coin.

Typically, coaxial light is effective for observing the interior of holes. However, when the nozzle or hole is narrow, even coaxial light cannot provide a clear view of the inside of the hole.

In practice, I tried capturing images using coaxial light, but it was not effective in capturing the interior of the nozzle.

Therefore, I tried using transmitted light from below to observe it.

By using transmitted light, the clogging inside the nozzle became visible.

	Planar light-source transmitted light RD-95T
	Stand with transmitted light GR-STD8

I will introduce various lighting options. Please feel free to contact our technical support for any inquiries.

Conventional coaxial illumination is often used at high magnification, utilizing only the central part of the spot, thereby minimizing the impact of illumination unevenness.

When the magnification is reduced, the surrounding area of the spot (where the illumination rapidly decreases) is used.

Our recommendation:

・Using a high-magnification zoom lens for coaxial illumination in combination with a x1.5 auxiliary lens (standard equipment).
The zoom lens dial is set to 0.7

・High-magnification zoom lens for coaxial illumination with the auxiliary lens at the tip removed (x1.0).
The zoom lens dial is set to 0.7

The edges of the screen may appear slightly darker, but it is still within the practical range.

・Using a high-magnification zoom lens for coaxial illumination in combination with a x0.75 auxiliary lens.
The zoom lens dial is set to 0.7

The increase in surrounding shadows makes it difficult to use effectively.

For observing a wide area with coaxial illumination, planar light-source coaxial illumination is effective.

(However, due to its lower light intensity, it cannot be used at high magnifications.)

(Camera → Half mirror →　Object of observation)

Coaxial light (spot)		Coaxial light (planar light source)

When observing the area marked with a red circle using standard ring lighting, the difference between halation and shadowed areas becomes significant, resulting in a highly difficult-to-observe image.

By using a four-segment LED ring light and illuminating only the longitudinal direction, halation can be suppressed.

Increasing the light intensity further enables the observation of the R-shaped area.	By increasing the magnification, the observation of the R-shaped area becomes easier.
By using an aperture lens, the depth of focus is increased, making the observation easier.
＜When the aperture is fully open＞	＜When the aperture is stopped down＞

However, using the aperture results in a decrease in brightness and a slight reduction in resolution. Therefore, with our lenses, the practical magnification range is up to approximately 120x.

When observing a blade made of metal, which has several surfaces at different angles and is prone to halation, lighting that allows independent adjustment of the height is effective.

The observation at 100x magnification was conducted by attaching the optional LED Angle LED-A2 to the high-magnification USB microscope FZ300PC3 (previous model) and adjusting the lighting position

　　　　　　　　　　　Height of the LED ring light

The basic observation methods are “Bright field observation” and “Dark field observation”.

1. Bright field observation

The most basic observation method involves illuminating the sample with uniform light from above for observation.

2. Dark field observation

This method involves shining light on the sample from a low angle or directly from the side, observing only the scattered or reflected light from the sample. The observed area (edges or protrusions) appears illuminated against a completely dark background.

There is dust on the surface of a resin plate coated with Teflon.

■ Bright field observation The surface structure of the resin is clearly visible, but the dust is not visible.		■ Dark field observation In a completely dark field of view, only the dust shines, and the surface structure is not visible.

＜Precautions for dark field observation＞

1. If the surrounding light is too strong, it may prevent effective dark field observation.

The two images above have the same low-angle lighting, but the appearance changes depending on the presence or absence of the desk stand.

2. The height of the lighting is crucial in order to illuminate only the observed object.

Mount the light slightly above the surface of the plate		Install the light at a position where it shines directly from the side.

Ring lights are commonly used in microscopes and magnifying devices.

It is suitable for applications that require bright illumination of a relatively confined (narrow) area.

Conversely, it is not suitable for achieving uniform brightness over a large area.

When a 15cm ruler is illuminated with a ring light, it appears as shown in the photo below.

We compared a sheet of white paper using a ring light and a stationary bar LED.

(Ring light) ＊The light distribution is significantly uneven.

(Stationary bar LED) 　*It can illuminate relatively evenly.

Depending on the size, a bar LED may be more suitable for industrial use.

Inspection tables equipped with bar LEDs, as shown in the photo below.

There are also stand-type (stationary) models, as shown in the photo below.

Additionally, there is the option to combine bar LEDs.

There are also professional square-type lights.
The photo below shows a model where the angle and illuminance of the four directional bar LEDs can be independently adjusted.
The bar LED is also a long type, with 120 LEDs integrated in one direction.
(Adjustments to the light angle and illuminance are possible.)

There is also the option to use photographic equipment as shown below.
(For photography, light intensity cannot be adjusted. *Adjustments must be made on the camera side.)

＊The following are both products from LPL Shōji Co., Ltd.

As LEDs begin to age, their brightness gradually decreases.
Typically, the lifespan is defined as the time it takes for the initial brightness to decrease by half.

Of course, if parts of the circuit, such as the solder joints, are susceptible to temperature or vibration and fail, the light may suddenly stop working. However, this would be considered a malfunction rather than normal aging.

The lifespan of LED components is provided by the component manufacturers, but it is a typical value rather than a guaranteed specification (e.g., approximately 20,000 hours ~ 100,000 hours).

When used in products such as LED ring lights, various other factors come into play.

(Ambient temperature, power supply conditions, and the heat dissipation structure of the product itself,…)

Our ring lights primarily use metal housings (for heat dissipation).

Some manufacturers, however, prioritize cost and opt for plastic housings.

Additionally, the lifespan varies significantly depending on whether the device is used near its maximum rating or at approximately half of its rated capacity.

The power supply environment also affects the lifespan.
We use a volume switch to ensure that the maximum illuminance is not reached immediately upon power-on.

If the volume is set to MAX and the power is switched ON/OFF using the power switch, there may be a risk of accumulated damage to the LED.

However, since the power supply environment can vary, it cannot be said universally that this is always problematic.

The occurrence of switching surges and other issues depends on the type of load connected to the same power supply.

The following is an example of a surge applied to the LED ring light when the volume is set to MAX, and a small solenoid is connected to the same power line while switching the power ON/OFF.

5V/div Measurement between the AC adapter and the controller.

The GR-10N has a fixed diffuser, so a filter cannot be attached directly as is.

In that case, one option is to purchase commercially available sheet-type polarizing film and apply it.

Polarizing film with a suitable level of rigidity, which can be cut with scissors, is convenient.

Cut it into a donut shape and attach it to the ring light using double-sided tape or similar adhesive.
(The following is not actual polarizing film, but an illustration of the process.)

Of course, it is necessary to place a polarizing filter not only on the light-emitting side but also on the light-receiving side.
For this, existing filters can be repurposed.

A polarizing filter is also placed on the light-receiving side.

Low-cost LED ring light GR10-N

The brightness (illuminance) varies significantly with the distance between the light source and the object.

It attenuates by the inverse square of the distance.

(Distance 5cm) 171100 lx	(Distance 10cm) 45100 lx Attenuates to approximately 1/4	(Distance 15cm) 16400 lx Attenuates to approximately 1/9

A “converging lens” is useful for minimizing the attenuation of illuminance over long distances.

Using a converging lens results in the following.

There are also lighting devices that incorporate a converging lens from the outset.

	Spot light LED-ZL3W
	When combined with a long-distance monocular lens, the following can also be achieved.

A 16mm CCTV lens and USB camera were set up, with the focal length adjusted to 200mm.

Under the above conditions, observation of a 80x60mm field of view is achievable.

The object is marked on a completely transparent glass surface (as shown below).

■ Ring light

Due to the wide observation range, which differs from that of micro lenses, the ring light results in complete reflection.

■ Dome light (indirect light)

The areas illuminated can be observed uniformly, but shadows (in the center) occur in the observation window area.

Additionally, even with a 150mm diameter light (the largest available from our company), a field of view of 80x60mm cannot be achieved.

■ Bar light

Using two 20cm bar lights to evenly illuminate the glass makes it easier to observe the glass itself.

■ Transmitted light

If the goal is to view transparent glass evenly, transmitted light offers the most stability.

We offer a variety of transmitted light solutions in different sizes.

Coaxial light is fundamentally used on “flat” surfaces with “gloss.” The limits of gloss and images for various applications have been verified.

In this instance, we conducted imaging using a microscope that allows switching between “coaxial light” and “ring light.”

(1) Subjects (regarding gloss)

Objects such as plated metals and silicon wafers, which are close to a “mirror finish”, can be observed accurately.

* Objects with surfaces close to a mirror finish will likely exhibit the effects of coaxial light more prominently.

So, at what level of gloss can we differentiate usage?

As a general guideline, a comparison can be made between a worn 10-yen coin and a new 10-yen coin.

・10-yen coin

A worn 10-yen coin is best suited for “ring light.”

However, if it is a new 10-yen coin, coaxial light is more suitable.

・1-yen coin

A worn 1-yen coin is suitable for both “coaxial light” and “ring light”.

* Both can be used, but coaxial light is more effective for surfaces with pronounced irregularities.

For detecting scratches, coaxial light is preferable.

(2) Subjects (regarding color)

Coaxial light is significantly influenced by differences in reflectance rather than color.

Even black surfaces can utilize coaxial light if they possess gloss.

・Black resin

　This is a glossy black resin that reflects light to the extent that the fluorescent light directed at the ceiling is visible.

* Both can be used, but coaxial light cannot reproduce colors. However, it does clearly highlight surface irregularities.

A characteristic of coaxial light is that reflectance has a greater impact on the image than color.

Even with significant color differences, it is not suitable for materials with uniform reflectance (diffuse reflectors).

・Printed materials

* If the variation in reflectance is consistent, using coaxial light will result in a flat image.

(3) Subjects (regarding transparent objects)

Transparent objects such as glass can be effectively illuminated using coaxial light, depending on the application.

It may be possible to observe the presence of surface coatings or fingerprints (oils) on the glass, provided there are variations in reflectance.

Observe fingerprints (oils) on the surface of the specimen slide.

* Fingerprints can be observed using coaxial light, but they are not visible at all with ring light.

Additionally, dust and foreign particles are easier to observe with coaxial light.

We also examined the cross-section of the specimen slide.

* In the case of glass, the observation can vary significantly depending on the polishing condition; however, for specimen slides, it appears that ring light is easier for observation.