LED Bulb / Tube / Panel
Lamp
An array of white LEDs plus a built-in driver in a retrofit shape — the lamp that ended a century of filaments. 100+ lm/W, 15,000–25,000 h life, instant start, and now the default light source for everything.
Schematic symbol
Lamp
How led bulb / tube / panel appears in a circuit diagram.
Types & variants
Key specs
Wattage & lumens
W / lmJudge by lumens, not watts: ~900 lm (9 W LED) replaces a 60 W GLS; a 20 W batten replaces a 36 W tube fitting.
Efficacy
lm/W90–130 lm/W typical; BEE star rating in India is based on this.
Colour temperature
K2700 K warm, 4000 K neutral, 6500 K cool daylight (the Indian favourite).
CRI
Ra≥80 for general use; ≥90 where colours matter. Cheap bulbs skimp here first.
Driver type
—Constant-current IC drivers flicker less; cheap capacitor-dropper bulbs flicker at 100 Hz and die sooner.
Surge rating
kVIndian voltage spikes kill bulbs — look for 2.5–4 kV surge protection claims.
Markings
Base or body prints wattage, voltage range (often 100–300 V 'wide voltage'), lumens, colour temperature and BIS mark. Tubes mark length, wattage and whether ballast bypass is required.
Standard values
Bulbs: 0.5 (night lamp), 3, 5, 7, 9, 12, 15, 20, 30–50 W (high-wattage). Battens: 10 W 2 ft, 20 W 4 ft. Panels: 6/12/15/18 W round or square. Street lights: 24–150 W.
How to choose
1) Pick lumens for the room, then the lowest wattage delivering them. 2) 6500 K for work areas, 2700–3000 K for bedrooms. 3) CRI ≥80, flicker-free driver, 2.5 kV+ surge rating for Indian mains. 4) Dimmable bulbs only with compatible trailing-edge dimmers. 5) For fully enclosed fixtures, check the bulb is rated for it — heat is what kills LEDs.
Pinout & package
Retrofit caps: B22, E27, E14, GU10, G13 (tubes). Inside: LED board (many chips in series/parallel), driver PCB, heatsink body and diffuser. Panels and battens integrate strips with an external or built-in driver.
Example circuits
- 9 W bulb anatomy: bridge rectifier → constant-current buck driver → 8–12 LEDs in series
- T8 LED tube in bypass wiring: mains directly to tube ends, choke and starter removed
- Emergency bulb: charging circuit + Li-ion cell + inverter that lights the LEDs when mains fails
- 12 V solar home lighting with MR16 LED spots
Common failures
One LED chip failing open kills the whole series string (dead or half-bright bulb), driver capacitor drying out (flicker then death), solder cracks from thermal cycling, and surge damage to the driver — the LEDs themselves rarely wear out first.
How to test
Visually check for a burnt/black LED chip on the board — bridging it with solder revives the bulb (at slightly lower brightness). Test driver output voltage across the string. A bulb flickering at 100 Hz has a failing smoothing capacitor; replace it and the bulb often lives again — LED bulbs are the most repairable lamps ever made.
Substitutes
Direct cap-for-cap replacement of every legacy lamp type. Within LEDs, match lumens, colour temperature and cap; for dimming or enclosed fixtures, match those ratings specifically.