Light Sensor Block

This sensor detects ambient (surrounding) light. Using data wires, it can send out the current light value and a logic signal (true/false) based on whether the current light value falls above or below a trigger point.

A trigger point is the specific value in a range of numbers where a change in condition occurs. For example, you might program your robot to move forward only when the light level rises above 60%. The trigger point would be 60.

Specify the trigger point by using the slider or by typing a number into the input box. To specify the range (above or below the trigger point) that will generate the "true" signal, use the radio buttons or the pull-down menu. The "true" portion of the range will be in color; the "false" portion will be gray.

The default setting for the light sensor block is for light levels above 50% to generate a "true" signal. The radio button to the right of the range is selected and the slider is set at 50. To switch the "true" portions of the range (setting values below 50% as "true"), you would select the left radio button.

The feedback box in the configuration panel shows the current light value. (To receive feedback, make sure that the light sensor is connected to the chosen port and that communication has been established with the NXT.)

You must drag at least one output data wire from this block’s data hub to another block for any information to be sent. (See the Data Hub section below for more information.)

Detecting the Light Sensor’s own Reflected Light

If you check the "Generate Light" checkbox, the light sensor will turn on its own small light source and detect this light if it is reflected back to it. This function is especially useful in difficult lighting conditions like very bright rooms. The function also allows the light sensor to serve as a short-distance range finder. With "Generate Light" turned on, a light sensor approaching a reflective object will detect higher reflected light levels. Therefore, it is possible to use the sensor to avoid running into obstacles.

Display Settings

1. The number shows which of your NXTs ports are connected to the light sensor. You can change this number in the configuration panel if you need to.
2. This icon indicates at what level the trigger point is set. The more colored bars displayed, the higher the trigger point.
3. This icon is displayed if "Generate Light" is turned on.
4. The block’s data hub will open automatically when the block is placed in the work area. At least one data wire must be dragged from the block’s output plug to another block’s data hub. (See the Data Hub section below for more information.)

Configuring the Light Sensor Block

1. Choose the port where your light sensor is plugged in. By default, the block will be set to port 3 for a light sensor. You can change this selection if you need to.
2. Use the slider to set the trigger value or type a value directly into the input box. Select the radio button to the right of the slider if you want the block to be triggered by light levels higher than the trigger value; select the left radio button to trigger the block with light levels lower than the trigger value. You can also use the pull-down menu to set the "true" portion of the slider.
3. If you check the "Generate Light" checkbox, the light sensor will turn on its own small light source and detect this light if it is reflected back to it.
4. The feedback box displays the current light reading (0-100%). You can use it to try out different trigger values.

Configuring the Light Sensor block’s Data Hub

You can control the Light Sensor block dynamically by connecting data wires (from other blocks’ data hubs) to the Light Sensor block’s data hub.

Open a block’s data hub by clicking the tab at the lower left edge of the block after it has been placed on the work area.

Data wires carrying input information to a block are connected to the plugs on the left side of its data hub. Data wires carrying output information are connected to the plugs on the right side.

[A] Input plug
[B] Output plug
[C] Number data wire (yellow)
[D] Logic data wire (green)
[E] Text data wire (orange)
[F] Broken data wire (gray)

Passing data from the input plug to the output plug

If an input plug has a corresponding output plug (see A above), the input data will pass through from the input plug to the output plug without being changed. In this case, you can only use the output plug if the input plug is connected to an input data wire; connecting an output data wire to such an output plug without a connected input data wire will cause the output data wire to be "broken" (and colored gray).

Data wires carry specific types of data

Each data wire carries a specific type of data between blocks. For example, if a data wire is dragged from a logic plug on a block’s data hub, it can only be connected to a logic plug on another block’s data hub. The chart below shows what kind of data each plug can accept or send out.

Data wire colors

Data wires are identified with specific colors: wires carrying number data are colored yellow, wires carrying logic data are colored green, and wires carrying text data are colored orange.

"Broken" data wires

If you try to connect a data wire to a plug of the wrong data type, the data wire will be broken (and colored gray). You will not be able to download your program if a data wire is broken.

If you click a broken wire you can read why it is broken in the small help window in the lower right corner of the work area.

Data must be within the possible range of the plug

If an input data wire transmits a value outside the possible range of the plug it is connected to, the block will either ignore the value or change it to a value within its range. For plugs that allow just a few input values (example: just 0, 1, or 2), the plug will ignore the input if a value arrives outside its range.

For plugs that accept larger input ranges (example: 0 – 100), the plug will force any input outside its range to fit. For example, if a Move block’s Power plug receives an input value of 150, the block will change the input value to 100 (i.e., a number within the Power plug’s range).

This chart shows the different characteristics of the plugs on the Light Sensor block’s data hub:

	Plug	Data Type	Possible Range	What the Values Mean	This Plug is Ignored When...
	Port	Number	1 - 4	1 = Port 1, 2 = Port 2, 3 = Port 3, 4 = Port 4
	Trigger Point	Number	0 - 100	Value to compare against
	Greater / Less	Logic	True/False	Logic used in comparison. True = Greater, False = Less
	Generate Light	Logic	True/False	Determines if the sensor's own LED is on or not
	Yes / No	Logic	True/False	Result of comparison
	Intensity	Number	0 - 100	Scaled value read from sensor.
	Raw Value	Number	0 - 1024	Raw (unscaled) value read from sensor