This document is a slideshow presentation about LEDs (light emitting diodes) and smart lighting. It discusses the basics of how LEDs work, including their semiconductor materials and band gap energies that determine photon wavelengths. Kirchhoff's voltage law and how it relates to diode circuits is also covered. The presentation explains how LED drivers can be used to efficiently power LEDs and describes planned experiments on determining LED turn-on voltages and measuring power consumption. The overall goal is to provide an overview of LEDs and introduce the topic of smart lighting technologies.

1. MODULE 4: LEDs
SUMMER CHALLENGE
Electrical Engineering: Smart Lighting
Prachi Shukla
PhD Candidate
Boston University
prachis@bu.edu

2. Boston University Slideshow Title Goes Here
Module 4: LEDs
Overview
 From “Lighting” to Smart Lighting
 What is a Diode?
 LEDs!
 Electrical Power
 LED Drivers
2

3. Boston University Slideshow Title Goes Here
Module 4: LEDs
Lighting & Color Science
 Visible Light is a form of electromagnetic radiation
 The human eye responds to the visible light spectrum
 White light is the presence of all colors
3
100km 10km 1km 100m 10m 1m 100mm 10mm 1mm 100μm 10μm 1μm 100nm 10nm 1nm
3kHz 30kHz 300kHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz 3THz 30THz 300THz 3PHz 30PHz 300PHz
780nm
380THz
400nm
750THz
Visible Light Spectrum
mm Wave Spectrum
microwave Spectrum

4. Boston University Slideshow Title Goes Here
Module 4: LEDs
Smart Lighting
 In what ways can light be better?
 Energy Efficiency
 Healthy Lighting
 Productivity (Data access)
4

5. Boston University Slideshow Title Goes Here
Module 4: LEDs
What is a diode?
 A device that allows current to flow in one direction;
always has polarity (e.g., LED)
 Forward Bias Voltage
 For current to flow, diodes require a turn-on voltage (i.e., forward bias
voltage)
 In an ideal diode, voltage drop remains constant
5
Cathode
Anode

6. Boston University Slideshow Title Goes Here
Module 4: LEDs
Kirchhoff’s Voltage Law
 The algebraic sum of all voltages in a loop must equal 0
 Relationship to Diode circuits
 Once the diode reaches the turn on voltage, 𝑉𝑅 increases with 𝑉𝑆
 Current through the circuit increases with increase in 𝑉𝑅
6
V0
I
R1
R2
V1
V2
A
+
+
-
-
𝑉0 + −𝑉1 + −𝑉2 = 0
+
𝑉𝑆
-
+ 𝑉𝐷 -
- 𝑉𝑅 +
𝑉𝑆 + −𝑉𝐷 + −𝑉𝑅 = 0

7. Boston University Slideshow Title Goes Here
Module 4: LEDs
LEDs
David Miller

8. Boston University Slideshow Title Goes Here
Module 4: LEDs
How Do LEDs Work?
 LED Materials
 Semiconducting materials: Resistance levels between those of a
conductor and an insulator
 Current can only flow in one direction
 Passing through the LED, electrons lose energy
 Lost energy creates photons
 Photons have discrete wavelength related to band-gap
 Band-gap width and energy
 The wider the band-gap, the greater the energy of the photon released
 Specialized materials & processes required to achieve wide band-gap
 Planck’s Relation:
E =
hc
l
E: Energy
h: planck constant
c: speed of light
λ: wavelength

9. Boston University Slideshow Title Goes Here
Module 4: LEDs
9
Conduction Band
Valence Band
Small Band Gap: Low Energy Red Light
Small Band Gap

10. Boston University Slideshow Title Goes Here
Module 4: LEDs
10
Conduction Band
Valence Band
Large Band Gap: High Energy Blue Light
Large Band Gap

11. Boston University Slideshow Title Goes Here
Module 4: LEDs
Experiment I
 LED circuit
 Determining the turn-on voltage
11

12. Boston University Slideshow Title Goes Here
Module 4: LEDs
Electrical Power
 Power is the rate at which energy is consumed.
 Power is measured in Watts [𝑊] or [J/s]
 Energy sources (such as batteries) produce power
while the load of the circuit absorbs power.
12
𝑃 = 𝑉𝐼 This is another one of those important equations…
+
𝑉𝑆
-
+ 𝑉𝐷 -
- 𝑉𝑅 +
𝐼 =
𝑉𝑅
𝑅
=
𝑉𝑆 − 𝑉𝐷
𝑅
𝑃𝐷 = 𝑉𝐷𝐼 =
𝑉𝐷 𝑉𝑆 − 𝑉𝐷
𝑅

13. Boston University Slideshow Title Goes Here
Module 4: LEDs
Electrical Power
 Combining the previous equation with Ohm’s
 Law:
 Consider a 60𝑊 incandescent attached to a 120𝑉 source
 How does current change if you replace the 60W bulb with 120W bulb?
13
𝑉 = 𝐼𝑅
𝑃 = 𝑉𝐼 = 𝐼2
𝑅 = ൗ
𝑉2
𝑅
60 = 120𝐼1 120 = 120𝐼2

14. Boston University Slideshow Title Goes Here
Module 4: LEDs
Experiment II
 LED Drivers
 Power Consumption
14

15. Boston University Slideshow Title Goes Here
Module 4: LEDs
Recap
 What did you today?
15