ARDUINO, DIY, Electronics, Inspiring, LEDs, photography, Raspberry Pi, Robotics

Experiments with a Light Meter

Why I am interested in Light meters?

When I was working in Scotland, I came across photo dynamic therapy (PDT), which uses light sensitive drugs to kill cancer cells. In the entire UK, there are only two PDT centers (afaik), one of which is in Dundee. By visiting the PDT center in Dundee, I realised that after applying the PDT drugs, doctors ask patients to wait in  sun light for two hours. There is no particular reason for exactly two hours of exposure to sun light. Therefore, it is not possible to know how much light dose has been received by the patients. To address this problem, PDT center at Dundee measured sunlight across the UK and Ireland and suggested that  cheap lux meters can be used to measure the required lux dose. I met with one of the PI and discussed about this in detail.

The problem with cheap light meters:

However, most commercially available cheap lux meters can only give instantaneous measure of light. These are originally developed for photographers to know lighting in their photo and building mangers to know lighting in a room. But PDT application  requires the lux values to be logged, aggregated to know whether the required light dose is reached. I think the only way to realise that is through connecting the lux meters to a microcontroller and stream the values to a smartphone. For that I am going to use a cheap lux meter that I can confidently modify after reading this blog post .

What I did:

I ordered the lux meter with a brand name “Ceto”from the same vendor as suggested in the blog post mentioned above. I identified the pins required to tap to get the lux values out. These are the pins on the amplifier. I soldered wires to these pins to read the voltage. So effectively LUX values are converted to voltage values in this lux meter. For example LUX of 290 is converted as 0.288V. I connected these wires to a multimeter to  see these voltage values.

IMG_20160722_234716581_HDR

Guts of the LUX meter

IMG_20160722_234721797

Zooming inside

IMG_20160722_234741644

Red wire is signal

IMG_20160723_241350983

Black wire is ground

IMG_20160723_241816577

Hot glue to keep the wires in place

IMG_20160723_242142465

Made a hole to the case to let the soldered wires come out, so that I can feed them into a multimeter

IMG_20160723_242159688

More hot glue to fix the wires to the case

IMG_20160723_242631030

Connected the wires to multimeter and we can see the light values appearing on the Multimeter as voltage values.

In the next step, I will connect the lux meter to a Arduino Uno and Bluetooth so that its possible to record the  aggregated lux values overtime time to determine the light dose for PDT treatment. I will write these details in another post.

P.S: It is just one of my hobby project, not related to my research.

Advertisements
Standard

2 thoughts on “Experiments with a Light Meter

  1. Doug Bates says:

    Do you really have sunshine in Cork? Here in Devon I think the therapeutic light dose would have to be extended somewhat 😉

    I know little about medicine but I guess there is some photo chemistry going on somewhere and if so, does the quality of the light matter? (BlueRed parts of the spectrum)? If so, are you going to arrange some sort of light filter or correct for the detector’s sensitivity across the spectrum?

    Footnote: I am currently playing around making a weather station using my Raspberry Pi (+SenseHat+anemometer & rain-gauge accessories from Maplin) and was thinking next step – ‘Hours of Sunshine’ sensor’. My next step was to look at using an LDR from the ‘CamJam’ #2 EduKit and tinker with the ‘gpiozero’ library, see: https://gpiozero.readthedocs.io/en/stable/api_input.html#light-sensor-ldr.

    I don’t offer this idea as better; LDRs have known shortcomings but are cheap and maybe sufficient for experimental purposes? Just an idea at the moment.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s