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Light Chamber & Control Room Description


The main purpose of this chamber is to provide high-intensity monochromatic or monochromatic combinations of wavelengths which allows for in vivo experimentation with (whole) plants. This is especially true where fluorescence monitoring can occur by saturating the entire plant with (especially) 405 nm violet light as well as other wavelengths of visible light. The light chamber is monitored and controlled from another room, and thus the high-intensity laser light is kept in isolation and people are safe from laser radiation exposure. Ten lasers bombard a central "light collector," which then acts as an artificial "sun." The chamber also provides the option of controlling ambient temperature, humidity, and other conditions during experiments. This is an advantage not provided with other types of instrumentation.


This first picture shows the chamber's front door open with all lasers turned off. There are 10 lasers with the following specifications:


4 - 405 nanometer X 500 milliwatts each

2 - 455 nanometer X 500 milliwatts each

1 - 455 nanometer X 2000 milliwatts

2 - 532 nanometer X 500 milliwatts each

1 - 532, 455, & 720 nanometer combined (white) X 200 milliwatts


Total power = 6,200 milliwatts.



The lasers are pointed at a central Light Collector which consists of "rippled" glass with a center - pillar made of solid aluminum and covered with mirrors on the inside of the Collector. This forms an artificial "sun." It allows the manipulation of narrow wavelengths of brilliant light.


For example, if I want to expose a plant leaf to a burst of 405 nanometer light (violet), I can then monitor the leaf for fluorescence using a camera, a soon-to-be installed USB microscope, and 4 light sensors which convert light intensity to a pulse output. The frequency of the output is a linear representation of light intensity.


All this is done from the safety of a control room nearby.



For the purpose of taking pictures for this report, one of the aluminum panels was taken off. But in full operation, the chamber is completely dark and isolated. The video camera has its own infrared emitters, so it can see in the dark. The camera is never pointed directly at the "sun," because in doing so, it will burn up the camera's "eye" in a few seconds.


The chamber allows larger objects (such as plants) to be exposed to very bright light either as white or monochromatic. Most fluorometers are very small and do not allow an entire plant or large object to be exposed to very bright light experiments in an enclosed area.



Beneath the light chamber is another area with relays and isolated 110 VAC control circuits (covered by the white panel). The main power supply for the lasers is in this area, and is 12 VDC at 30 amps. The power supply in the control room is 0 - 30 VDC at 5 amps. The left-hand display (see close-up picture) of the control room power supply shows the current consumption by each of the secondary relays. When a secondary relay turns on, the control room power supply shows its current draw, and the secondary relay (mounted to the control board inside the light chamber) turns on a primary relay. Primary relays are mounted to the circular support for the lasers. So when a switch is turned on in the control room, it sends 6 volts to a secondary relay in the light chamber. The secondary relay then turns on a primary relay on the circular support for the lasers. Once the primary relay turns on, a 12 VDC signal is sent to the control room and turns on an LED indicator on the front panel indicating that the specific relay is on.



The wires from the main laser power supply are heavy gauge (number 10 wire), and ground for all connections is centered on a large copper ground plane. The lasers are turned on by the primary relays in sets in most cases.

There are 2 - violet lasers in a set, another 2 - violet, 2 blue, 2 green, 1 - high power blue, and 1 - white laser (RGB). Each of the primary relays can handle up to 10 amps. Each of the secondary relays can handle up to 5 amps.

As noted in the picture, when I took this picture I bumped the glass light collector - so it is crooked. It is normally level. The camera is pointed downwards, and the camera's case shields it from direct exposure from the artificial "sun" when all lasers are on. The infrared LED's provide the color camera with the ability to see in the dark. The LED's surround the camera lens. The output of the camera is sent to the video monitor in the control room.

I have a USB microscope which will be mounted near plant leaves (or other materials or objects) exposed to laser light. This will be viewed on a PC monitor in the control room. The microscope can magnify up to 500 times, and the software allows recording of its images. Hopefully, this will give me some good video footage of leaf fluorescence (as one example).


An engineer friend from Germany suggested that I use light-to-frequency chips (TCS3210). These chips have built-in filters and they put out pulses according to the intensity of the peak wavelength they are monitoring. I have wired the 4 sensors to monitor the following:

Green 524 nm peak wavelength

Red 640 nm peak wavelength

Blue 470 nm peak wavelength

Clear - no filter

The range set for their output is 2 Hz to 120 KHz, and you can monitor wave period, frequency, or use other methods such as integration and pulse accumulation in a data harvesting scenario.

I do have 2 monochromators I can use as well. I can attach these sensors to the output slit and look for a specific wavelength instead of a spectral range.


The light chamber control board is mounted alongside the copper ground plane, and has LED voltmeters to show the main power supply voltage going out from the primary relays. It also has LED monitors to show when a secondary relay coil is active. The primary relay coils are 12 volts, and the secondary relay coils are 5 volts. The wired connector (44 conductor) goes to a cable which sends and receives signals from the control room.

I am still working on the control room, but the basic setup for running the lasers is working. Lights on the front panel show which lasers are on, and voltmeters show the power that is present on the secondary relay coils. Current is shown in milliamperes.


Since I started, I added the circuitry for receiving the pulses from the 4 light to frequency converter boards. The signals are 2-wire differential to cancel out noise and to allow longer distances if necessary (75ALS193).



Below is the 4-sensor board and the other board has (so far) a power supply, a volt meter which allows me to monitor the voltage at all times. The light sensor outputs go to a CD4049 CMOS chip which buffers the low current signals. Then they go to the inputs of a 75ALS192 RS422 differential driver. This is tied via a CAT5e cable to the control room, where a differential receiver picks them up and converts them back to TTL level signals. These are tied (for now) to a 4-trace 70 MHz storage oscilloscope.  Right now I am monitoring the signal's frequency and period to see the effects of various wavelengths of light from various sources including the 10 lasers. Most of the wires are covered by aluminum foil to protect them in case a laser beam gets out of alignment. The foil is also grounded to shield the signals from noise.


Below is a close-up of the 4 sensors plugged into a zero-insertion-force socket. This socket allows me to easily change a sensor if it goes bad. Also, the sensors are configured using wiring underneath the socket, so that if a change is needed I won't have to deal with such small parts.



I had to solder the 8-pin SOIC chips to 8-pin DIP adapters so they would fit this socket, which requires 0.1" spacing. This was very difficult, since I didn't have any surface-mount tools! I had to wear magnification glasses and use the tiny tip on the end of my smallest soldering iron.


Below is a picture of the board running and the voltmeter shows 5.05 VDC going to the 4 light sensor / converters.



I have done some preliminary testing simply by placing the light sensors in the bottom of the light chamber. Below are pictures of waveforms from my oscilloscope in the control room. The first picture has text labels for which sensor each oscilloscope channel is monitoring.  After that, the channel allocations are all the same:



Channel data:

Channel 1 (No filter) - 1.38 KHz

Channel 2 (470 nm) - 300 Hz

Channel 3 (640 nm) - 641 Hz

Channel 4 (524 nm) - 359 Hz

Conditions: Chamber had 2,000 milliwatts 405 nm laser light only, and the infrared camera was turned off. Horizontal was set to 5.0 milliseconds per division.

Below is an example of what happens when the infrared camera is turned on:


Channel data:

1 14.77 KHz

2  15.3 KHz

3  18.6 KHz

4  18.27 KHz

Conditions: IR camera turned on in total darkness. The IR camera has 8 - IR LED's and the camera is pointed down, directly at the light sensors. No lasers were on. Horizontal was set to 20 microseconds per division.

When any lasers were turned on with the camera running, the frequency went down - not up - which didn't make sense to me.


IR camera on + all lasers on:

1 1.07 KHz

2  684 Hz

3  150 Hz

4  167 Hz

To me, this suggests that the coherent light from the lasers saturated the  light sensors and effectively blocked all (incoherent) infrared from the camera's LEDs. No laser light hit the sensors directly (as a beam) or as a reflected beam. All laser light is diffused by the glass light collector and fills the entire chamber evenly.

I also asked Peter Schmalkoke, an engineer from Germany (with over 30 years experience in electronics) about this decrease in frequency with an increase in light levels, and this was his answer:

Hi Randy

I guess your light sensors are heavily overloaded with light
when the lasers are turned on.

Most semiconductor-based light sensors have their maximum sensitivity
in the red/IR range of the spectrum. This applies to camera sensor
chips as well. Hence the IR irradiation can be kept at low levels for
most cameras in order to produce useable images. So your IR source
will be producing a relatively low level of light intensity compared
to the laser sources. I remember I found your lasers impressive
regarding their power levels. Unfortunately the TAOS/AMS company
doesn't provide a chart showing the coherence between light intensity
and output frequency including the range of optical overload.

Internal to the chip, the photo sensors will be operated with a circuit
similar to that shown with the LED based color sensitive light sensor
(see link below):

There is an operational amplifier connected to the photo sensor and I know

there are FET based operational amplifiers that exhibit an intuitively unexpected behavior
when overloaded at the input: The output signal is not only limited,
but (rather suddenly) decreases dramatically and the polarity is even
reversed. Such an effect might be at work with your sensor chips.

I would suggest you attenuate the light levels at the sensors
(at least for a diagnostic experiment), e.g. by covering them with
a piece of aluminum foil or black cardboard, perforated with some
random pin holes. I guess this should restore the linearity at the
light intensity level you're working with. For optimal results the
size and/or number of those holes must be adjusted, of course.

Regards, Peter

Another thing I noticed is that the pulses generated by lights with a DC power supply produced a continuous waveform. But the lights powered by AC power supplies produced wave patterns according to the period of sine waves in the power supply. Here is an example picture of what I saw:


You can see that the variations in the time period of pulses for all of the light sensors (being directly proportional to the intensity of the light produced by the light source) were an indication that light sources powered by AC line voltage modulate the amplitude of the light produced. I wonder how this might effect the growth of plants, and the mood and ability to work for humans (or animals).



There was a lot of jitter in the waveforms; had I not had a storage oscilloscope, I don't think I could have seen the details of waves produced by the light sensors. I am also wondering why there are so many over-shoot and under-shoot spikes on the waveforms. Using a differential driver and receiver pair should have eliminated most of the noise.


The main purpose of this chamber is to provide high-intensity monochromatic or monochromatic combinations of wavelengths which allows for in vivo experimentation with (whole) plants. This is especially true where fluorescence monitoring can occur by saturating the entire plant with (especially) 405 nm violet light.


There are several possibilities for data mining and interpretation:

1. Sending the frequency data to spectrum analyzer software in a computer.

2. Using my custom-built dual processor board to monitor the time period of waves generated by the light sensors for both excitation and emission intervals; using other types of custom-built hardware to do the same.

3. Using instruments provided by manufacturers which have the capability of data mining via serial interface to a computer, as long as complete isolation for users can be maintained from the light chamber.


4-23-16; revised 5-14-16

Randy A. Stahla