Light, Light Sensor , Circuit of Light Sensor and Algorithm of Light circuit

The light sensor is a unique tool that can come in handy for numerous uses such as measuring objects and detecting objects. The tool is used in labs for scientists, in offices for the general work force and in home security systems.

Definition

A light sensor is a mechanical device sensitive to light, temperature, radiation level, that transmits a signal to a measuring or control instrument, according to Dictionary.reference.com. 

Similar to how the human eye is sensitive to light and body hair is sensitive to nearby objects, the light sensor is a tool that is sensitive.

Function

This instrument can be used to give information on distance, shape, speed, dimensions and types of substances contained in various objects, depending on the area of study it is being used for. 

With a high level of precision, they are used for measuring purposes in architecture and offset printing. (A type of printing process used by large commercial printers. The ink doesn't press directly on the paper, it is distributed from a metal plate to a rubber mat where it then proceeds to the paper.

Proplem Definition

Nobody doubts the important role played by light on crops. The greenhouse must collect a maximum of sum radiation all day long in winter, and every morning  and every evening all the year round to get a favourable thermal balance from short IR and allow active photosynthesis through the “visible” (provided no factor involved in the process falls down to the minimum, i.e. is missing to a certain extent .

The intensity or the level of light, has a vital effect in the velocity of  the photosynthesis  process which is essential to all green plant , the duration of light, or day length, also has profound photoperiodic influence; and sources of artificial light, as distinct from sunlight, have different simulative effects on plants.

Types of artificial lighting are; Tungsten filament, Discharge lamps, and Fluorescent lamps.

The Effective reflection ensures that the maximum amount of light is concentrated on mum amount of light is concentrated on the plants being treated.

The main roles for lighting in greenhouse are:

1-To allow working on short winter days or in the evening.

2-To provide day-length manipulation or night-break techniques by the use of low intensity tungsten filament lights, suspended above the plants.

3-To supplement the natural daylight when if falls below at level sufficient to maintain optimum photosynthetic activity, and to improve vegetative development and flower truss initiation a high intensity light .

4-To illuminate growing rooms.

How we solve the problem?

We control the light of greenhouse using PIC microcontroller and light sensor LDR which sense the intensity of light in the greenhouse and if the light is not enough an external lamp switched on compensating the low light .

Light Dependent

Light-dependent sensors are inexpensive and commonly used for gauging and responding to light levels. These light sensors work as automatic switches for different devices. They belong to a group called photoresistors because their resistance increases as light levels increase, which is why they're commonly present in outdoor lights like streetlamps. As light levels increase, their resistance increases and turns the lights off or down.

we will use LDRLight Dependant Resistor in our system control.

Why LDR?

·        Automatic Headlight Dimmer

·        Night Light Control

·        Street Light Control

·        Position Sensor

·        The relation between LUX and resistance is linear as shown in figure

Algorithm:

1-set the setting point of the light intensity of greenhouse according to the type of plant on the greenhouse.

2-The sensor contimously sensing the light intensity in the greenhouse  as variation in its resistor.

3-The sensor enter its analog signal to A/D converter.

4-The A/D converts the analog signal into digital signal giving it to the controller.

5- The controller compare the signal coming from the sensor with  the setting point :

-If the light intensity coming from the sensor is less    than the setting point   then

Lamp is turned on .

-else

The lamp still off.

How do you connect LDR sensors with a PIC ??

It will not work with just the LDR. You need to measure voltage at one of the ADC inputs. The voltage comes from a potential divider made from a fixed resistor and the LDR in series with the ADC connected to the center. If you omit the fixed resistor the LDR will pull the PIC input high, even under dark conditions and the ADC will always read maximum voltage.

Note that there are two ways you can connect this: 
1. LDR goes to the supply, resistor goes to ground.
2. Resistor goes to supply, LDR goes to ground.

Option 1 will give an increasing voltage as it gets brighter but you have to carry the supply line wherever the LDR is mounted. If it shorts to anything you could damage the supply or the wiring.

Option 2 will give a decreasing voltage as it gets lighter but this is easy to compensate in software. It has the advantage that the LDR is grounded at one end and the resistor limits the current, giving some degree of protection.

The optimum resistor value will give best voltage swing between lightest and darkest conditions. Typically, choose a value equal to the mid way between LDR dark and LDR light resistances.

There are just two ways of constructing the voltage divider, with the LDR at the top, or with the LDR at the bottom:

You are going to investigate the behavior of these two circuits. You will also find out how to choose a sensible value for the fixed resistor in a voltage divider circuit.

Remember the formula for calculating V_out :

 The block diagram of the light circuit is as the following