LED lighting....why the hate?

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
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Finelld
Posts: 32
Joined: Tue Jul 26, 2022 7:35 am

Re: LED lighting....why the hate?

#61 Post by Finelld » Thu Aug 11, 2022 3:54 am

There are pluses and minuses to all lighting technologies. I am a degreed professional photographer and electronics engineer.

From a photography perspective the number of spectral lines within the bandwidth of a given light source is less important than the bandwidth and color temperature. Keep in mind that color imaging sensors see only RGB. Most have IR blocking filters because CCD and CMOS sensors are particularly sensitive to red wavelengths. Many LED light sources used by photographers have adjustable color temperatures. This is achieved by having an array of two different color temperatures of “white” LEDs and adjusting the ratio between them. Photographers are experts at modifying lights and lighting with the use of flags, gels, reflectors, and a whole host of light sources. But 99.9% of them aren’t concerned with spectral purity, linearity or if a given line is present or missing. LEDs are more efficient at producing many of the lines used in fluorescence and diode solid state lasers are often used to pump other lasers or non linear optics to get higher optical frequencies and shorter wavelengths. One nice thing about LED illumination is that the color spectrum is comparatively constant over their output power levels when compared to incandescent illumination.

Black body illumination has the benefit of having a more complete spectrum in relation to LEDs but it is weighted towards the IR and thermal IR spectrums. As a result it is very inefficient for optical illumination. Another serious draw back is the spectrum or color temperatures changes as the brightness is adjusted. In order to radiate in the shorter wavelengths like greens and blues you need to dump more power to generate higher quantum energy states to emit these wavelengths. The use of gasses like halogens can improve this but it isn’t a perfect solution.

The last light source I will cover can be considered as two light sources. They are arc lamps and fluorescent lamps. For higher power lights these can encompass the best of both worlds or at least create a compromise between the two previous technologies. They require more support components to work but they are more efficient than incandescent lights. They can be designed to have a phenomenally complete optical spectrum. They lack the amount of dimming capability of LEDs and incandescents. They can also have strong lines in the UV spectrum. HID lamps fall into this category. In the 1980s Streamlight made a light called the Streamlight 1,000,000. It was a bulky handheld HID light that required an external battery pack or belt. It was used by NASA and law enforcement. At the time it had the closest spectral completeness to the sun of any other light source. It was featured in NASAs annual spin-off magazine for technologies spun off from the space program.

Most types of illumination are fine for most types of microscopy. The biggest time you need to worry about specific spectral lines is when doing fluorescence microscopy. The other time is when measuring spectral absorption of parts of a sample.

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ashamartin
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Joined: Fri Sep 23, 2022 11:21 am

Re: LED lighting....why the hate?

#62 Post by ashamartin » Fri Sep 23, 2022 11:26 am

The reason behind hating LED light is this flicker that is still far too rapid to be seen directly, but some people can see multiple images of the lamps every time they make a saccade, which is unpleasantly distracting. The flickering of these LEDs may limit the uptake of the bulbs, just as many people dislike energy-saving fluorescent lamps.

Dubious
Posts: 391
Joined: Sun May 09, 2021 7:55 pm

Re: LED lighting....why the hate?

#63 Post by Dubious » Fri Sep 23, 2022 2:35 pm

ashamartin wrote:
Fri Sep 23, 2022 11:26 am
The reason behind hating LED light is this flicker that is still far too rapid to be seen directly, but some people can see multiple images of the lamps every time they make a saccade, which is unpleasantly distracting. The flickering of these LEDs may limit the uptake of the bulbs, just as many people dislike energy-saving fluorescent lamps.
That subliminal flicker is caused by PWM--pulse width modulation--used to vary the light output of some LEDs by varying the duty cycle. But, PWM should no longer be an issue, as today there are many constant-current LEDs whose brightness is adjusted by varying the voltage, or that use PWM at such a high frequency as not to cause eyestrain. You just need to be careful in selecting the LED and driver. Note that PWM was also until recently a serious problem with the backlighting for many laptops/monitors/TVs, and still is with some...

LouiseScot
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Joined: Tue Jul 07, 2020 1:51 pm
Location: Scotland

Re: LED lighting....why the hate?

#64 Post by LouiseScot » Fri Sep 23, 2022 2:38 pm

Dubious wrote:
Fri Sep 23, 2022 2:35 pm
ashamartin wrote:
Fri Sep 23, 2022 11:26 am
The reason behind hating LED light is this flicker that is still far too rapid to be seen directly, but some people can see multiple images of the lamps every time they make a saccade, which is unpleasantly distracting. The flickering of these LEDs may limit the uptake of the bulbs, just as many people dislike energy-saving fluorescent lamps.
That subliminal flicker is caused by PWM--pulse width modulation--used to vary the light output of some LEDs by varying the duty cycle. But, PWM should no longer be an issue, as today there are many constant-current LEDs whose brightness is adjusted by varying the voltage, or that use PWM at such a high frequency as not to cause eyestrain. You just need to be careful in selecting the LED and driver. Note that PWM was also until recently a serious problem with the backlighting for many laptops/monitors/TVs, and still is with some...
The previous post was spam which I reported earlier
Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

richbart
Posts: 66
Joined: Thu Jan 28, 2021 2:07 pm
Location: Iowa, USA

Re: LED lighting....why the hate?

#65 Post by richbart » Mon Sep 26, 2022 7:12 pm

I switched toLED On my BH2 BHTU.I think the photos are better. I sold a microscope to someone in histology, and they wanted halogen, because specific features showed up better with halogen. Just depends on what your doing.

Dubious
Posts: 391
Joined: Sun May 09, 2021 7:55 pm

Re: LED lighting....why the hate?

#66 Post by Dubious » Mon Sep 26, 2022 7:39 pm

All in all, my eyes prefer halogen. But from any engineering point of view, LED lighting has to be vastly superior--just take a look at the size/weight of the external power supply for the Nikon E800's 100w halogen lamp.

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