Low Cost Bili-Light Radiometer

designed by Greg Nusz and Advait Kotecha

The objective of this instructable is the production of a low-cost, easy to use, low-maintenance device for measuring the efficacy of phototherapy lights bili-lights for the treatment of hyperbilirubinemia (jaundice). The purpose of this device is to measure the output of phototherapy units and to ensure that the emitted light is intense enough (>4uW/cm2/nm) within the correct wavelength range (425 - 475nm).

The device operates by filtering the incident light through blue-glass filters. The light that passes through the filters is then collected by a solar cell where it generates a current that is read as the device output via an onboard ammeter. Because the measured current is generated by the incident light, no other power source is needed.

Directions for Use:
The meter should be held the same distance and direction from the bililight as the baby receiving treatment. The needle indicator in the red indicates that insufficient light is emitted by the light in the wavelength range 425-475nm, and the bulbs should be replaced. The needle indicator in the green indicates that there is sufficient blue light in the therapeutic window to treat hyperbilirubinemia.

Limitations
The primary limitation for this device is related to the filter inability to completely block infrared (IR) light. Since silicon has a high responsivity even the 5% that passes through the filter can contribute to the signal and thus cause false positive readings in the presence of IR. For this reason, the radiometer will not provide accurate readings for incandescent bulbs are outdoors. However, most bililights in use are either fluorescent or LED-based.

The documents attached are a word document version of this instructable as well as a instruction sheet in doc and pdf format.

This device was developed in cooperation with Engineering World Health. For more info on EWH, visit their website http://ewh.org/

Step 1: Parts List

34mm Blue Colored Glass Filter x 2
Pegasus Associates Lighting PCGF-MR11-BLU 2 @ $5.90 = $11.80

0-1mA DC Ammeter
Marlin P. Jones & Assoc. 8726 ME $13.95

Solar Cell 0.5V, 300mA
Edmund Scientific Item # 3081612 $6.95

Project Box: HAMMOND Multipurpose Instrument Enclosure 4.72 in x 3.15 in x 2.17 in
Newark Electronics, Newark Part Number: 87F2528, Manufacturer Part No: 1591TSBK
$5.84

Fasteners $0.20

Total $38.74

Comments

[GorillazMiko]

looks a little complicated, but looks cheap too!

[Normjr]

I must disagree! I believe that this is a professionally constructed and well written Instruction! It appears to be Inexpensive, NOT CHEEP, like all of those mint box constructs. Kudos to you GJNusz! What might the uses of this project be in the non-clinical world?

[jongscx]

I actually beg to differ. It's actually pretty simple, just an ammeter hooked up to a solar cell, and some blue filters in front... It is; however, really detailed. How do you calbrate it though? I'm assuming you'd need to get a baseline at the hospital/med equipment store first.

[GJNusz]

Calibration was performed by using a commercially available Olympus Bilimeter (~USD$2000). Samples were taken at various bililight intensities and we plotted the ammeter output versus the Olympus reading. The ammeter response response was linear throughout a large range of light intensities(R > 0.99). The calibration current was then determined by where this line crossed the minimum therapeutic intensity of 4uW/cm^2/nm.

The three prototype units I've made have calibration currents at 0.12 mA, 0.18 mA and 0.14 mA. Ideally, each unit would be calibrated independently by some device like the Olympus Bilimeter as jongsx mentions.

Although, perhaps as more are built we can collect some statistics on calibration currents and see how much it varies from device to device.