# Light Intensity (PPFD/PAR)

The PAR sensor detects light in the photosynthetically active 400-700 nm waveband. The light_intensity command reports photosynthetic photon flux density (PPFD) in µmol photons m⁻² s⁻¹ (see Sensors). In contrast to the other sensors, the PAR sensor can also control the output of LEDs with an emission peak in this waveband. The light_intensity, previous_light_intensity, and set_light_intensity commands support this control.

# Ambient Light Intensity

To replicate the ambient light intensity using the MultispeQ's LEDs, the ambient light intensity needs to be read from the PAR sensor and used as a setting for the intensity of the non pulsed lights.

To measure the ambient light intensity just add the light_intensity command to the protocols environmental array.

"environmental": [
    [ "light_intensity" ],
    ...
],

Then the light intensity can be set for the non pulsed lights in the nonpulsed_lights_brightness array, using the light_intensity command.

"nonpulsed_lights": [
    [ 2 ],
],
"nonpulsed_lights_brightness": [
    [ "light_intensity" ], ...
],

This works for simple Protocols, as well as advanced Protocols using the _protocol_set_ command.

# Previous Light Intensity

When using the light_intensity command to set the light intensity for a non pulsed light, with multiple protocols in a _protocol_set_, in each protocol the intensity also needs to measured, using the light_intensity command with the environmental array. In a longer running protocol, this would result in a fluctuating light intensity, especially when taking measurements outside. If the initially measured light intensity, is supposed to be used throughout the _protocol_set_, instead of light_intensity, previous_light_intensity can be used to set the non pulsed light intensity.


"_protocol_set_": [
    {
        // First Protocol in the set, measuring the light intensity
        "environmental": [
            [ "light_intensity" ],
            ...
        ],
        "nonpulsed_lights": [
            [ 2 ],
        ],
        "nonpulsed_lights_brightness": [
            [ "light_intensity" ], ...
        ],
    },
    {
        // Second Protocol in the set, using the previous light intensity
        "nonpulsed_lights": [
            [ 2 ],
        ],
        "nonpulsed_lights_brightness": [
            [ "previous_light_intensity" ], ...
        ],
    }
]

# Light Intensity Update

The value for previous_light_intensity is updated whenever the following commands are used:

light_intensity within the environmental array
par_led_start_on_open, par_led_start_on_close and par_led_start_on_open_close with the Protocol flow control

Note

If the light intensity was never measured using the light_intensity command in the environment array, previous_light_intensity will return zero.

# Set Light Intensity

Instead of using the light intensity reading from the PAR sensor, you can also manually set the light intensity using the command set_light_intensity. This becomes useful when a certain light intensity should be used rather then using the measured ambient. In this case, the commands for light_intensity and previous_light_intensity together with non pulsed lights will use the value defined in ser_light_intensity instead of the sensor reading.

In the following example, PPFD is set to 500 µmol photons m⁻² s⁻¹.

"set_light_intensity": 500,   //(requires one integer, not a float)
"nonpulsed_lights": [
    [ 2 ],
],
"nonpulsed_lights_brightness": [
    [ "light_intensity" ], ...
],

← Sensors Repeats →