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