Table 2: LED optical characteristics at Tc = 25 degrees

We chose the LED based on surgical lighting requirements such as: Homogenous light (good illumination with on various surface) High central Illuminance (lux) between 40,000-160,000. The central Illuminance is measured at a distance of 1m from the surface High color temperature (4,000 – 4,500K or higher) Color rendering index (85 -100)

Other surgical light requirements are: Light field diameter called D50 should not exceed 50% of the d10 diameter Backup possibility in case of interruption of the power supply

AggiE-Challenge: Universal Surgery Light Bulb Replacement for Engineering World Health Olivia Harrington1, Ibukun Oni1, Keegan Smith1, Stanley Jacob1, Astride Tchoffo2, Greg Merrill3, and Rafael Moreno4

Meagan Saldua Harris1 and Kristen Carlson Maitland1

Department of Biomedical Engineering1, Electrical Engineering2, Mechanical Engineering3, Industrial Distribution4

Dwight Look College of Engineering, Texas A&M University

• Developing countries face many healthcare problems mainly due to poor socio-economic growth and development.

• A vast majority of medical equipment used in developing countries are donations of old equipment from Western countries.

• The problem with those donations is that 39% are dysfunctional upon arrival, 58.5% will be dysfunctional after 5 years in service, and only 2.5% will be functional for more than 5 years.

• In developing countries, surgery light bulbs are expensive to replace and not always locally available. Therefore, our aim is to design a universal, low-cost surgical light that is suitable to environment and has a long life time.

Introduction

Mechanical Design

Electrical Design of the prototype included an LED driver circuit powered by the solar charged batteries to stabilize the current in the LED. Circuit Components include • LM3404 –Current Regulator • Ron-75kΩ Resistor • Cb-0.01µF capacitor • Cf-0.1µF Capacitor • L1-22µH inductor • Rsns- (.3Ω) used 2.2Ω • Cin- 3.3µF • D1- 1A (40V) • 9V Battery • LZ1-00CW00 (LED) The solar Panel was Used to charge the 9V battery used in the Driver Circuit. Table 1: Comparison of surgical light specs vs. LEDs

Electrical Design

Results and Testing

Challenges and Future Direction

This semester our team has • Researched standards for surgical light bulbs and looked at design ideas • Visited hospitals in order to understand how surgical light bulbs are used • Measured light intensity and tested capabilities of LED in the lab • Developed an electrical circuit capable of powering three LEDs • Designed a prototype using SolidWorks Next semester: • Adjust design based on student feedback after Rwanda trip • Implement design and build prototype • Receive feedback from engineers and students regarding prototype • Improve prototype and build up to the final design

Why materials and designs were chosen • Aluminum is used throughout the design because of its heat capacity • LEDs are used because they are efficient and low-costing • A clamp is used in order to make the structure adaptable • Reflective material will be used to distribute the light • An adjusting mechanism will be used to control distribution of light CAD models

Parameter Symbol Typical Unit

Luminous Flux Φv 227 lm

Luminous Efficacy η 90 lm/W

Correlated Color Temperature CCT 5500 K

Color Rendering Index (CRI) Ra 75 Unitless

Viewing Angle 2Θ1/2 85 Degrees

Total included Angle Θ0.9V 125 Degrees

Distance from floor (m) Power (µW)

0.5 46

0.75 22.2

1 13

1.5 5

1.93 3

0

20

40

60

0 1 2 3

Po

we

r (µ

W)

Distance from floor (meters)

Light Intensity of an LED

LED Other Surgical Lights

Long Lasting (up to 50 000 Hrs.) Shorter Lifespan (up to 30 000 Hrs.)

Energy Efficiency (~85% better) More Energy Consumption

Less Cost Efficient More Cost Efficient

Figure 5: LED Driver Circuit

Modification of the circuit after testing • The 0.3Ω resistor was changed to a 2.2Ω Table 4: Measurement of current through the LED with different voltages Table 5: Measurement of the light intensity of an LED:

Input Voltage Output Current

9V 50mA

6V 70mA

Figure 3: Isometric View of Light Bulb with LEDs embedded

Figure 2: Isometric View of Adjusting Mechanism for Light

Solar panel with rechargeable batteries • Low cost, Eneloop AA batteries can be charged 1500 times • Use 2 or more sets of batteries to cycle from the surgery light to a charger Some specifications needed for our solar panel and batteries were: • Nickel-metal hydride chemistry to accept trickle-charge • Higher solar panel voltage • Higher battery voltage than circuit • Solar panel current less than 10% of batteries’ total capacity • Enough battery capacity to power the light for an extended time

Power

Figure 7: Graph of an LED’s power

Figure 1: Cost hurdles faced by the hospitals in these countries..

Figure 4: Students testing out the LED.

Figure 6: Solar Panel used to power the LED Driver circuit

Illumination Analysis