Until around 1998, there were no usable LEDs in the color blue. For decades, researchers tried to develop this color - without success. The invention of efficient blue LEDs paved the way for energy-saving white light sources - and earned Isamu Akasaki, Hiroshi Amano and Shuji Nakamura the Nobel Prize in Physics in 2014.
Because blue light not only shines blue, but is an integral part of the color spectrum. No white without blue. The world of blue LEDs will continue to develop due to their clear advantages.
LED PROPERTIES - high efficiency with less heat
Electrical energy can be converted relatively efficiently into blue light, especially for deep blue, i.e. wavelengths around 450 nanometers (nm). According to the manufacturer, the radiation efficiency is in the >50 percent range. The manufacturer Osram currently even states an efficiency of 75 percent for its LED (Oslon® SSL 150 GD CSHPM1.14). We have determined the radiation efficiencies in W/W for all typical LED colors. We used a spectroradiometer for the measurement.
This revealed the following trends:
- Spectral properties of the blue LED: Peak wavelength (WL): 452.90 nm; Peak full width at half maximum (FWHM): 18.13 nm; Full width at 20 intensity %: 40-60 nm
- Spectral properties of the white LED: White light LED: Peak WL 440.00 nm; Peak FWHM 18.33 nm; 2nd peak WL 551.00 nm; 2nd FWHM 126.00 nm
- The peak wavelength of the white LED is almost the same as that of the blue LED
- However, blue LEDs offer higher efficiency. The efficiency of “Deep Blue” LEDs with wavelengths around 450 nm is directly stated as 52 percent or 0.52 W/W. This means that 52 percent of the electrical power in watts that is fed into the LED is subsequently converted into light energy. In contrast, the corresponding value for red light is approximately < 40 percent and for green light only around 20 percent.
The high efficiency of blue can therefore be utilized in two ways: If the light source is to provide a comparable irradiance, the electrical current fed into the blue LEDs can be reduced. However, if the same current is fed into the LEDs, this leads directly to a higher irradiance, but with a higher efficiency than with longer wavelengths. In both cases, this means that less heat is generated at the LED.
Development of a new generation of telecentric lenses
A new generation of blue LEDs makes a new generation of telecentric lenses useful, as the newly developed telecentric measuring lenses with a telecentric beam path now enable double the resolution or double the depth of field compared to conventional systems. This means that all the advantages of the blue LED can now really be utilized in their application.
These new telecentric measuring lenses were developed by Vision & Control, one of the innovative pacesetters for industrial image processing. The company has been at home in image processing for over 30 years and has introduced numerous innovations.
Advances in telecentric lenses enable system integration to utilize high potential resolution and depth of field in blue light imaging. This will be a helpful building block for efficient and high-resolution image acquisition in the machine vision process chain.
We have developed a new generation of telecentric lenses for use in industrial image processing with state-of-the-art color correction that extends deep into the blue spectral range. This means that all the advantages of the new generation of LEDs - blue and white - can now also be used in measurement and inspection applications. However, the new telecentric lenses are also very suitable for all conventional LED colors.
Advantages of the new “blue” telecentric lenses
A special feature is the broadband color correction, which has been extended deep into the blue spectral range. This means that the lenses can now be used for the entire visible spectrum and the near infrared.
The light color used in an image processing application should always be taken into account, as blue LEDs have a number of advantages.
In the efficient and high-energy blue spectrum, for example, they deliver maximum sharpness with the greatest possible depth of field. Image sharpness is almost doubled due to the lower diffraction compared to infrared. - They are also ideally suited to the spectral composition of white LEDs with their peak around 450 nm and exhibit excellent imaging properties. Compared to the even shorter wavelength UV, blue light has the advantage of visibility, which makes handling the image processing system easier and safer. - Visibility provides a defensive reaction of the eye. On the other hand, the visibility of the radiation makes it easier to set up the system.
Several lens series are currently available for imaging a maximum object field diagonal of 18 mm to 125 mm. Within each series there is a lens type for the common sensors from 1/4“ or 1/3” up to DX format for format-filling imaging of the respective object field. The lenses for sensors up to 1.2” have a C-mount connection, the version for the DX format is equipped with an M42 thread connection.
They are broadband corrected for the visible spectral range and the near infrared, but with a color correction that extends deep into the blue spectral range. This makes them very suitable for blue LEDs including “deep blue” LEDs and also for white LEDs as they have a strong blue light component. Like all our standard lenses, they have an adjustable, lockable aperture with aperture number marking and offer robust mechanics so that they can withstand harsh industrial conditions. - They therefore continue to offer all the advantages of conventional telecentric lenses for industrial image processing.
published in ELEKTRONK PRAXIS