These cookies do not store any personally identifiable information. You can set your browser to block or alert you about these cookies, but some parts of the site will not then work. They are usually only set in response to actions made by you which amount to a request for services, such as setting your privacy preferences, logging in or filling in forms. Strictly Necessary Cookies: (Always Active) These cookies are necessary for the website to function and cannot be switched off in our systems. After we finish updating our website, you will be able to set your cookie preferences. AuthorĪnalog Devices is in the process of updating our website. Also, unfavorable converter stage amplification factors can impact the quality and thus the result of the circuit. With the circuit shown in Figure 1, light intensity can be converted into an electrical value for further data processing in a relatively simple way. ConclusionĮrror sources such as bias currents and offset voltages of the components must be considered. GAIN = gain factor of the internal amplifier,įor further noise reduction, a common-mode and a differential filter are used on each of the differential inputs of the ADC.Īll of the depicted components are extremely power-saving, making the circuit ideal for battery-operated portable field applications. Thus, the output code for the measured voltage is as follows: For this purpose, ADCs with multiple differential inputs can be used, such as the 16-bit ADC AD7798. Analog-to-Digital Conversionįor further processing of the measured values, the photodiode current that was first converted into a voltage has to be provided to the microcontroller as a digital value. (ADI) is a good choice for these applications. With a bias current of typically 1 pA and a maximum offset voltage of 1 mV, the AD8500 from Analog Devices, Inc. A low offset voltage should also be present. Current-to-Voltage Conversionįor a high quality current-to-voltage conversion, the minimal bias current of the operational amplifier is desirable because the output current of the photodiode is in the picoampere range and thus can cause considerable errors. V FS,P-P represents the desired full output voltage range (full-scale, peak-to-peak) and INT MAX the maximum light intensity, which is 120,000 lux for direct sunlight. For this, the short-circuit current (I SC) of each diode has to be taken from the data sheet and subsequently the sensitivity, S (pA/lux), at the operating points determined from it. However, the relative sensitivities of the red, green, and blue diodes are different, so the gain of each stage must be determined separately through the feedback resistance R FB. Characteristic curves of current to light intensity for red, green, and blue photodiodes. The light intensity measured via the photodiodes can now be used to control the light source according to the requirements of the respective plants.įigure 2. Here, three differently colored photodiodes (green, red, and blue) are used, which respond to different wavelengths. By controlling parts of the spectrum and the intensity of light exposure throughout various life stages, growth can be maximized, and the yield ultimately increased.Ī corresponding circuit design for measuring the light intensity over the visible spectrum, in which plants are photosynthetically active, is shown in Figure 1. As a rule, light in the wavelengths of the green and yellow regions of the spectrum is reflected and contributes only slightly to growth. Most plants usually absorb light in the wavelengths of the red, orange, blue, and violet regions of the visible spectrum. Light is thereby one of the most important factors in smart agriculture. Here, one key task is to monitor and control important plant parameters that contribute to maximizing plant growth and accelerating photosynthesis. In the era of the Internet of Things (IoT), however, light intensity also plays an important role in so-called smart agriculture. Use photodiodes which are sensitive to red, green, and blue light.ĭetermination of the light intensity can be crucial, for example, if you want to design the lighting of a room, or in preparing for a photo shoot. How could I measure the light intensity of different light sources? Answer: How to Convert Light Intensity Into an Electrical Quantity
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