# LEDlights.org

> LEDlights.org is an encyclopedia of light-emitting diodes (LEDs). It explains LED history from 1907 to today, semiconductor physics, every LED package and display technology, real-world applications, and offers free browser calculators. Every article opens with a definition and every section opens with a 40–60 word direct answer. The history and physics articles carry no advertising or affiliate links; product cards on the applications, types and tools pages are labelled. The automotive section shows example lamps from GENSSI, a lighting brand under the same ownership as LEDlights.org.

Core facts used consistently across the site:

- An LED is a semiconductor p–n junction diode that emits light by electroluminescence; photon wavelength λ (nm) ≈ 1240 / band gap Eg (eV).
- Commercial LEDs span ~210 nm (UV-C) to ~1,600 nm (infrared); typical forward voltage is 1.2–3.6 V (up to ~7 V for UV-C).
- White LED luminous efficacy is 80–230 lm/W in commercial products; the laboratory record is 303 lm/W (Cree, 2014).
- Rated lifetime is 25,000–100,000 hours to L70 (70% of initial light output), measured under IES LM-80 and projected with IES TM-21.
- More than 95% of white LEDs are phosphor-converted: a 445–455 nm InGaN blue chip plus a YAG:Ce (yellow) and often a nitride red phosphor.
- Color quality: CRI (CIE 13.3) Ra 80 is the commercial minimum, Ra ≥ 90 with R9 ≥ 50 is recommended for homes, Ra ≥ 95 for art, film and surgery; IES TM-30 adds Rf and Rg.
- The 2014 Nobel Prize in Physics went to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for efficient blue LEDs.

Citation: please cite "LEDlights.org" with a link to the specific page.

## Encyclopedia articles
- [Light-emitting diode](https://ledlights.org/): The complete reference on light-emitting diodes: how LEDs work, their history from 1907 to MicroLED, every LED type from 5 mm to COB and WS2812B, applications from homes to headlights and grow lights, and free LED calculators.
- [History of the LED](https://ledlights.org/history/): The full history of the light-emitting diode, from H. J. Round's 1907 carborundum glow and Oleg Losev's patents to Holonyak's red LED, the Nobel-winning blue LED, white light and MicroLED.
- [How LEDs work](https://ledlights.org/how-leds-work/): A clear technical guide to how LEDs work: p-n junctions, electroluminescence, band gap and wavelength, LED materials and forward voltage, white light, lumens and efficacy, CRI and CCT, thermal design, drivers and PWM dimming.
- [Types of LEDs](https://ledlights.org/types/): The complete guide to LED types: 3 mm and 5 mm DIP, SMD 2835, 3528, 5050, 5630, 3030 and 5730 specs, COB, CSP, filament, high-power, OLED, QLED, Mini-LED, MicroLED, IR, UV-C and addressable WS2812B, with a sortable comparison table.
- [LED applications](https://ledlights.org/applications/): How LEDs are used everywhere: A19, BR30, PAR38 and GU10 bulbs, circadian lighting, high-bays, stadiums, streetlights and traffic signals, OLED and Mini-LED screens, matrix headlights, aviation and marine lights, horticulture PPFD, medical photobiomodulation, Li-Fi and sensing.
- [LED calculators and tools](https://ledlights.org/tools/): Free LED calculators: series resistor (nearest E24 value, color bands, power rating), lumen and wattage equivalents, and energy savings with payback and ROI for metal halide, HPS and fluorescent retrofits.

## In-depth guides
- [CRI and CCT: the color of LED light](https://ledlights.org/physics/cri-and-cct-kelvin-guide/): A practical guide to LED color temperature (CCT in kelvin, 1,800–10,000 K) and color rendering (CRI Ra, R9, TM-30 Rf and Rg, MacAdam steps), with an interactive spectrum slider and recommended CCT and CRI for kitchens, bathrooms, bedrooms, offices, retail and museums.
- [LED drivers and flicker](https://ledlights.org/physics/led-drivers-and-flicker/): How LED drivers work: constant current vs constant voltage, linear vs switch-mode, power factor and inrush, PWM and CCR dimming, TRIAC, ELV, 0–10 V, DALI and DMX control, and how to measure and limit flicker with percent flicker, Pst LM and SVM under IEEE 1789 and EU ecodesign rules.
- [LED lifespan: L70, LM-80 and TM-21](https://ledlights.org/physics/led-lifespan-l70-lm80/): How LED lifetime is defined, tested and projected: L70, L80 and L90 lumen maintenance, B10 and B50 failure fractions, IES LM-80 testing, TM-21 projections and the 6× rule, LM-84 and TM-28 for lamps and luminaires, the real causes of LED failure, and how many years a rated lifetime means.
- [SMD 2835 vs 5050 vs 3030](https://ledlights.org/types/smd-2835-vs-5050-vs-3030/): SMD 2835 vs 5050 vs 3030 (plus 3528 and 5630) compared: package sizes drawn to scale, watts, lumens per watt, thermal pads, LED strip densities, and which chip to choose for strips, bulbs, panels, grow lights and RGB.
- [COB vs SMD vs CSP](https://ledlights.org/types/cob-vs-smd-vs-csp/): Chip-on-board (COB), surface-mount (SMD) and chip-scale package (CSP) LEDs compared: construction, heat paths, lumen density, beam and shadow quality, color consistency, efficacy, reliability, cost and the best uses for each, with an interactive cross-section.
- [OLED vs QLED vs Mini-LED vs MicroLED](https://ledlights.org/types/oled-vs-qled-vs-miniled-vs-microled/): How OLED, QLED, Mini-LED and MicroLED displays make light, compared on contrast, brightness, color, burn-in, lifetime, power, price and best uses, from phones and laptops to TVs and modular video walls.
- [LED bulb shapes and base types](https://ledlights.org/guides/led-bulb-shapes-and-bases/): A complete chart of LED bulb shapes (A19, A21, BR30, BR40, PAR20, PAR30, PAR38, MR16, GU10, G25, B11, T8, T5) and lamp bases (E26, E27, E12, E14, E17, E39, B22d, GU10, GU5.3, G9, G4, GU24, G13), with diameters, metric names, lumen-to-watt equivalents, beam angles, Type A/B/C LED tubes and compatibility tips.

## Interactive calculators
- [LED Series Resistor Calculator](https://ledlights.org/tools/#resistor): Calculates the current-limiting resistor for one LED or a series string from supply voltage, forward voltage and current, then picks the nearest standard E24 value, shows its color bands and checks the power rating.
- [LED Lumen/Wattage Equivalent and Energy Savings Calculator](https://ledlights.org/tools/#energy): Converts incandescent, halogen and CFL bulbs, or metal-halide, high-pressure sodium and fluorescent fixtures, into equivalent LED lumens and watts, and estimates annual kWh, cost and CO2 savings, lamp replacements avoided and, for commercial retrofits, the net cost after rebates, simple payback and 5-year return.

## Reference tables
- [LEDs compared with incandescent, halogen, CFL, fluorescent and HID lamps](https://ledlights.org/#why-leds): on Light-emitting diode
- [LED semiconductor materials, band gaps, colors and forward voltages](https://ledlights.org/how-leds-work/#materials): on How LEDs work
- [Ways to make white light with LEDs](https://ledlights.org/how-leds-work/#white-light): on How LEDs work
- [MacAdam ellipse steps (SDCM) and visible color difference](https://ledlights.org/how-leds-work/#binning): on How LEDs work
- [LED color temperatures (CCT) and where to use them](https://ledlights.org/physics/cri-and-cct-kelvin-guide/#cct): on CRI and CCT: the color of LED light
- [Recommended CCT and CRI for each room and space](https://ledlights.org/physics/cri-and-cct-kelvin-guide/#by-room): on CRI and CCT: the color of LED light
- [Constant-current vs constant-voltage LED drivers](https://ledlights.org/physics/led-drivers-and-flicker/#cc-vs-cv): on LED drivers and flicker
- [LED dimming control methods compared](https://ledlights.org/physics/led-drivers-and-flicker/#dimming-controls): on LED drivers and flicker
- [LED flicker metrics and limits](https://ledlights.org/physics/led-drivers-and-flicker/#flicker-metrics): on LED drivers and flicker
- [LED lifetime ratings: L and B values explained](https://ledlights.org/physics/led-lifespan-l70-lm80/#lumen-maintenance): on LED lifespan: L70, LM-80 and TM-21
- [LED lifetime in years at typical usage](https://ledlights.org/physics/led-lifespan-l70-lm80/#life-claims): on LED lifespan: L70, LM-80 and TM-21
- [SMD LED package sizes, power and output](https://ledlights.org/types/#smd-naming): on Types of LEDs
- [Infrared LEDs: 850 nm vs. 940 nm](https://ledlights.org/types/#infrared): on Types of LEDs
- [Ultraviolet LED bands, wavelengths and uses](https://ledlights.org/types/#ultraviolet): on Types of LEDs
- [Addressable LED chips: WS2812B, WS2815, SK6812 and APA102](https://ledlights.org/types/#addressable): on Types of LEDs
- [SMD 2835, 3030, 5050, 3528 and 5630 LED packages compared](https://ledlights.org/types/smd-2835-vs-5050-vs-3030/#compared): on SMD 2835 vs 5050 vs 3030
- [LED strip chips: density, power and output per metre](https://ledlights.org/types/smd-2835-vs-5050-vs-3030/#strips): on SMD 2835 vs 5050 vs 3030
- [COB vs SMD vs CSP LED packages compared](https://ledlights.org/types/cob-vs-smd-vs-csp/#at-a-glance): on COB vs SMD vs CSP
- [OLED vs QLED vs Mini-LED vs MicroLED compared](https://ledlights.org/types/oled-vs-qled-vs-miniled-vs-microled/#compared): on OLED vs QLED vs Mini-LED vs MicroLED
- [Recommended illuminance (lux) by space and task](https://ledlights.org/applications/#lux-levels): on LED applications
- [LED beam angles and typical uses](https://ledlights.org/applications/#beam-angles): on LED applications
- [IP ratings for LED fixtures (IEC 60529)](https://ledlights.org/applications/#ip-ratings): on LED applications
- [Grow light PPFD, photoperiod and DLI targets by crop](https://ledlights.org/applications/#grow-spectrum): on LED applications
- [LED bulb shapes: codes, diameters and uses](https://ledlights.org/guides/led-bulb-shapes-and-bases/#shape-codes): on LED bulb shapes and base types
- [LED lamp bases: codes, sizes and where they are used](https://ledlights.org/guides/led-bulb-shapes-and-bases/#base-codes): on LED bulb shapes and base types
- [Lumen equivalents: incandescent, halogen, CFL and LED watts](https://ledlights.org/tools/#lumen-equivalents): on LED calculators and tools
- [Commercial fixture equivalents: metal halide, HPS and fluorescent to LED](https://ledlights.org/tools/#commercial-equivalents): on LED calculators and tools
- [Typical LED forward voltage by color](https://ledlights.org/tools/#quick-reference): on LED calculators and tools

## Downloads
- [LED Engineer's Reference Cheat Sheet (PDF)](https://ledlights.org/downloads/led-engineers-reference-cheat-sheet.pdf): two printable pages covering color temperature (Kelvin) and CRI by room, SMD LED package sizes, Ohm's law and the series-resistor formula, forward voltage by color, lumen equivalents and key formulas

## Optional
- [Full text for language models](https://ledlights.org/llms-full.txt): every definition, section answer, glossary entry, specification table and FAQ in one Markdown file
- [XML sitemap](https://ledlights.org/sitemap.xml): all pages with last-modified dates