Lighting Technologies: Fluorescent, LED,

Cheatsheet Content

1. Fluorescent Lamps 1.1 Principle of Operation Gas Discharge: An electric current passes through an inert gas (e.g., argon, krypton) mixed with a small amount of mercury vapor. UV Emission: The electric discharge excites mercury atoms, causing them to emit short-wave ultraviolet (UV) light. Phosphor Conversion: The inside of the glass tube is coated with a phosphor material. When UV light strikes the phosphor, it fluoresces, emitting visible light. Ballast: Required to provide a high voltage to initiate the discharge and then regulate the current to maintain a stable arc. 1.2 Components Glass Tube: Contains the gas mixture and mercury. Electrodes: Typically tungsten, at each end of the tube, heated to emit electrons. Phosphor Coating: Converts UV to visible light. Different phosphors produce different color temperatures. Mercury Vapor: Essential for UV emission. Inert Gas: Facilitates the initial discharge. Ballast: Magnetic Ballast: Older, heavier, can cause flicker, less efficient. Electronic Ballast: Newer, lighter, eliminates flicker, more efficient, instant start, can be dimmable. 1.3 Types Linear Fluorescent (T-series): T12, T8, T5 (diameter in eighths of an inch). T5 and T8 are most common for efficiency. Compact Fluorescent Lamps (CFLs): Miniature versions, often with integrated ballasts, designed to fit incandescent sockets (see Section 3). Circline Fluorescent: Circular tubes. 1.4 Advantages High luminous efficacy ($50-100 \text{ lm/W}$). Long lifespan ($7,000-20,000$ hours). Lower heat output compared to incandescent. Good color rendering index (CRI) available. 1.5 Disadvantages Contain mercury (environmental concern for disposal). Require a ballast. Can flicker with magnetic ballasts. "Warm-up" time to full brightness. Performance degrades in cold temperatures. Limited dimming capabilities (requires specific ballasts). UV emission, though mostly absorbed by phosphor, can be a minor concern. 2. Light Emitting Diodes (LEDs) 2.1 Principle of Operation Electroluminescence: A semiconductor device that emits light when an electric current passes through it. PN Junction: Consists of a p-type semiconductor and an n-type semiconductor. Electron-Hole Recombination: When forward biased, electrons from the n-side recombine with holes from the p-side in the depletion region. Photon Emission: During recombination, energy is released in the form of photons (light). The color of the light depends on the band gap energy of the semiconductor material. White Light Generation: Phosphor Conversion: Most common. A blue LED chip is coated with a yellow phosphor. The blue light excites the phosphor, which emits yellow light. The combination of blue and yellow appears white. RGB Mixing: Red, Green, and Blue LED chips are combined to produce white light. Less common for general illumination due to complexity and control. 2.2 Components LED Chip (Die): The semiconductor material where light is generated. Substrate/Heat Sink: LEDs generate heat at the PN junction; efficient heat dissipation is crucial for performance and longevity. Encapsulant/Lens: Protects the chip and directs/shapes the light. Phosphor Layer: For white LEDs. Driver: An electronic circuit that converts AC power to the low-voltage DC power required by the LED, and regulates the current. 2.3 Types DIP (Dual In-line Package) LEDs: Older, lower power, used for indicators. SMD (Surface Mounted Device) LEDs: Common for general lighting, various sizes (e.g., 2835, 5050). COB (Chip-on-Board) LEDs: Multiple LED chips packaged as a single module, high lumen output from a small area. Filament LEDs: Designed to mimic incandescent bulbs, using multiple small LED chips on a transparent substrate. 2.4 Advantages Extremely high luminous efficacy ($80-150+\text{ lm/W}$). Very long lifespan ($25,000-50,000+$ hours). No mercury or hazardous materials. Instant on, no warm-up time. Excellent dimming capabilities. Directional light emission (reduces need for reflectors). Durable, shock-resistant (no filament). Operates well in cold temperatures. Compact size, allowing for flexible designs. 2.5 Disadvantages Higher initial cost (though rapidly decreasing). Performance is sensitive to temperature (requires good heat management). "Blue light hazard" concern (high blue light content in some white LEDs). Color shift over time (minor). Driver compatibility issues with older dimmers. 3. Compact Fluorescent Lamps (CFLs) 3.1 Principle of Operation Essentially a miniaturized fluorescent lamp with a built-in electronic ballast. The glass tube is typically bent or coiled to fit into a compact space, often resembling a traditional incandescent bulb. The integrated electronic ballast converts incoming AC power to high-frequency AC, which then excites the mercury vapor, producing UV light that is converted to visible light by a phosphor coating. 3.2 Components Coiled Glass Tube: Contains mercury vapor and inert gas, coated with phosphor. Electrodes: At the ends of the tube. Integrated Electronic Ballast: Located in the base of the bulb, converts AC to high-frequency AC for the lamp. Screw Base: Typically Edison screw bases (E26/E27) to directly replace incandescent bulbs. 3.3 Types Self-Ballasted (Integrated) CFLs: Most common, screw directly into incandescent sockets. Pin-Base (Non-Integrated) CFLs: Require a separate ballast in the fixture, often used in commercial downlights. 3.4 Advantages Much higher luminous efficacy than incandescent bulbs ($40-80 \text{ lm/W}$). Significantly longer lifespan than incandescent bulbs ($6,000-15,000$ hours). Lower heat output than incandescent. Available in various color temperatures. Direct replacement for incandescent bulbs (integrated CFLs). 3.5 Disadvantages Contain mercury (environmental hazard if broken or improperly disposed of). Warm-up time to full brightness. Performance degrades in cold temperatures. Can be bulky or aesthetically unappealing to some. Limited dimming options (specific "dimmable" CFLs needed, often not as smooth as incandescent/LED). Frequent switching on/off can shorten lifespan. Lower lifespan and efficiency compared to LEDs. Some generate radio frequency interference. 4. Comparison Summary Feature Fluorescent Lamps LEDs CFLs (Integrated) Principle Gas discharge, UV to visible (phosphor) Electroluminescence (semiconductor junction) Miniature fluorescent with integrated ballast Efficacy ($\text{lm/W}$) $50-100$ $80-150+$ $40-80$ Lifespan (hours) $7,000-20,000$ $25,000-50,000+$ $6,000-15,000$ Mercury Content Yes No Yes Warm-up Time Yes No (instant on) Yes Dimming Limited (special ballast) Excellent (with compatible driver) Limited (special bulb/dimmer) Cold Temp Perf. Degrades Excellent Degrades Durability Fragile glass Very durable (no filament) Fragile glass Initial Cost Moderate Highest (decreasing) Lower than LED, higher than incandescent Power Factor Can be low (magnetic), high (electronic) Typically high (good driver) Variable, often lower than LED