Dear researchers,
I'm working on the effects of different LED light qualities on growth and development of grafted watermelon seedlings during healing and acclimatization period.
The problem is that we do not have access to spectrometer and we want to determine our wavelength of (red:blue) and (white) treatments. However two of my light treatments are monochromatic Blue with the wavelength of 460nm and Red with the wavelength of 620nm (according to the catalog).
I have used 128 red LED and 64 blue LED in one square meter chambers.
first, I want to know that if I can calculate the wavelength of my R:B treatment by wavelength of each diodes.
second, I want to know that if there is a way to calculate the wavelength of white treatment without using spectrometer.
Thank you in advance
Moein.
See for each wavelength you are interested in calculating its wavelength if you can pass that through an aperture and notice diffraction patterns (Newton's rings). The central circle is called the Airy disk and the formula relating to wavelength and radius is well known https://en.wikipedia.org/wiki/Airy_disk
If you don’t have access to a sophisticated spectrometer, but simply want to find out the wavelength (without highest level of precision) then you may create your own spectrometer by for example setting up a simple diffraction grating set up to measure the wavelength as described in the following link: https://www.chemedx.org/blog/simple-method-measure-wavelength-light
Alternatively, you may use a simple rotating table spectrometer to measure the wavelength using a grating spectrometer used for teaching such: https://www.youtube.com/watch?v=jBUkTNY6fUk or using a CCD camera system such as: https://www.sciencedirect.com/science/article/pii/S0030399203001348
the approaches indicated above will provide information about the wavelengths present. In case of the white light, you should expect the overlap of various wavelength, so seeing the envelope of all of the lines present may not be easily obtained using a grating rotating spectrometer, but a CCD camera system may allow observing the spectral distributions.
There are also low resolution wavelength measurements using smart phones, such as: http://physicsbuzz.physicscentral.com/2013/02/turn-your-phone-into-spectrometer-for.html
You don't need any spectrometer, as the spectral densities of various LEDs, as functions of frequency, or wavelength, are well-documented [1]. If one were able to place all LEDs at one point, their spectral densities would essentially add up (neglecting interference, which is reasonable). What you need is some simple modelling, along the lines of [2]. Note however that in contrast to the assumption in [2], LEDs do not radiate energy isotropically, but anisotropically, inside a cone (this is achieved by equipping each LED with a lens). The modelling is most simple when assuming that each LED radiates isotropically inside its own cone and nothing outside it. Given the geometric distribution of the LEDs in your system, all you need to do is finding for each point at the surface of the plants the cones whose cross sections with the plant surface overlap at that point. The spectral density of radiation at that point consists of a superposition of the spectral densities of the relevant LEDs, each weighted by the cosine of the angle of the line linking the point at issue with that LED as measured from the axis of revolution of the LED's cone (consult [3], where in section 'Property' [4] the value of irradiance Ee is seen to be proportional to cos(α)).
[1] https://en.wikipedia.org/wiki/Light-emitting_diode
See, for instance,
[1a] https://en.wikipedia.org/wiki/File:RGB_LED_Spectrum.svg
[1b] https://en.wikipedia.org/wiki/File:White_LED.png
For the actual modelling, you will have to consult the product documents published by the manufacturers of the LEDs you are using.
[2] https://lhsblogs.typepad.com/files/cpo-worksheets-light-and-optics.pdf
[3] https://en.wikipedia.org/wiki/Irradiance
[4] https://en.wikipedia.org/wiki/Irradiance#Property
Usually LED is not absolute monochromatic light, half width will be different, it is best to see the actual spectrum, it is recommended to contact the manufacturer to provide the luminescence spectrum of the corresponding product.
The labels on the package say the color (as long as you believe the package)
The White LED, the color is defined in temperature. It is not accurate, but 5500-6500 Kelvin is the temperature of a bulk filament that would make the same color. In this case I can tell you that is bluish white and similar to the color of daylight. That said, there is no real white LED. In reality it is a mix of a yellow phosphor coated on a blue LED which gives blue and yellow peaks which your eye thinks is white. Thin phosphor coatings will look more blue. Thick phosphor coatings will look more yellow. Do a web search for white LED spectrum.
WL = Wavelength which has the Greek symbol Lambda which looks like an upside down v. The units are typically in nano-meters which would be a lower case nm.
Your Blue LED has a peak wavelength of 460-462.6nm. The peak of the spectrum will be there. Though you do not know how wide the spectrum is, you can do a web search for blue GaN LED spectrum and get something typical.
The Red LED has a peak wavelength of 620-630nm They give a range due to manufacturing variation. Also the peak will move a small amount with current and temperature.
So for your application, maybe that is enough.
If you wanted to measure the wavelength, then that is what a spectrometer is built for.
A very simple cheap way to show the two colors of the white LED is to use a audio CD as a reflective diffraction grating. Bounce the LED light off the CD and onto the wall and see the colors separate.
When I could not afford my own spectrometers I used this method to make my own simple spectrometer and actually calibrate it.
I would propose the following solution:
You can use linear colour filters to pass the wavelength range you want from the incident light source. All what you need then is to use calibrated photo detectors
to measure the optical power contained in the passed wave length range.
You can yourself make a photodetector by photdiodes or phototransistors or even a solar cell. For the linear colour filters please look at the link: https://oceanoptics.com/product/linear-variable-filters/
Best wishes
hello dear moein
You can use of seconic 7000 for your work. my phd thesis is the effect of different spectral LED lights on the growth, physiological and biochemical characteristics and gene expression ofanthocyanin pathways, and i used of seconic 7000 my work. you and Dr. Salehi can call to Dr saman aliniaefard and asked your question for this problem.
good luck
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