| L, symbol for inductance | Magnetic fields and inductance |
| L1, "hot" wire designation | "Ladder" Diagrams |
| L2, "neutral" wire designation | "Ladder" Diagrams |
| Ladder circuit / logic gate equivalents | Digital logic functions |
| Lagging phase shift | AC Phase |
| | Calculating Power Factor |
| laminated core | Hysteresis and Eddy Current |
| laminated iron core | Energy losses |
| Laser diode | Laser diodes |
| latch vs. flip-flop | Edge-triggered latches: Flip-Flops |
| Latch, D | The D latch |
| Latch, gated S-R | The gated S-R latch |
| Latch, S-R | The S-R latch |
| Latch-up | Common-Mode Gain |
| | High-impedance voltmeter |
| Latched state | NOR gate S-R latch |
| latching | The Shockley Diode |
| Law of cosines | Trigonometry Reference |
| Law of sines | Trigonometry Reference |
| LC resonance | Simple parallel (tank circuit) resonance |
| Lead, test | Safe meter usage |
| lead-acid battery | Electron activity in chemical reactions |
| | Practical considerations |
| Leading phase shift | AC Phase |
| | Calculating Power Factor |
| leakage current | Diode ratings |
| | Diode Characteristic |
| leakage inductance | Mutual inductance and basic operation |
| | Stray capacitance and inductance |
| leakage, capacitor | Electric fields and capacitance |
| LED | Voltmeter usage |
| | AND gate |
| | Light-emitting diodes |
| LED flasher | Long Duration Minimum Parts Red LED Flasher |
| | Long Duration Blue LED Flasher |
| | Long Duration Flyback LED Flasher |
| | Long Duration Red LED Flasher |
| LED sequencer | LED sequencer |
| Left-hand rule | Electromagnetism |
| Lenz's Law | Inductors and calculus |
| | AC Inductor Circuits |
| level switch | Switch types |
| Light Emitting Diode | AND gate |
| light-emitting diode | Voltmeter usage |
| | Light-emitting diodes |
| lightning | Nonlinear Conduction |
| limit switch | Switch types |
| Limits, calculus | Calculus Reference |
| line decoder | Decoder |
| | Demultiplexers |
| | Multiplexers |
| Line, polyphase system | Three-Phase Y and Delta Configurations |
| linear | Nonlinear Conduction |
| linear induction motor | Linear induction motor |
| linear taper potentiometer | Sensitive audio detector |
| | Potentiometer as a Voltage Divider |
| | Sensitive voltage detector |
| Linearit | Strain gauges |
| Lissajous figure | Frequency and Phase Measurement |
| Litmus strip | pH measurement |
| Litz wire | Inductor quirks |
| load | Resistors |
| Load, nonlinear | Power quality measurement |
| Loading, voltmeter | Voltmeter impact on measured circuit |
| Lock-out/Tag-out | Safe practices |
| Lodestone | Permanent magnets |
| Logarithm | Algebra Reference |
| Logarithm, common | pH measurement |
| Logarithm, natural | Solving for unknown time |
| Logarithmic scale | Ohmmeter design |
| Logic gate / ladder circuit equivalents | Digital logic functions |
| logic gate shape symbols | Shift Register, Parallel-in, Serial-out |
| Logic level | Digital signals and gates |
| logic simplification | Introduction |
| Logic, Aristotelian | Introduction |
| Logic, fuzzy | Introduction |
| Look-up table | Look-up tables |
| Loom, Jacquard | Memory with moving parts: "Drives" |
| Loop antenna | Principles of radio |
| loss | Decibels |
| Low, logic level | Digital signals and gates |
| low-pass filter | Low-Pass Filters |
| LSB | Decimal versus binary numeration |
| LVDT | AC Instrumentation Transducers |
