An LED chip is a doped-semiconductor sandwich. Electrons flow from the n-side, holes from the p-side. They meet at the junction, recombine, and release energy as a photon. The bandgap of the semiconductor (GaN for blue, AlGaInP for red) determines wavelength. White LED = blue chip + yellow phosphor (downconversion) or RGB mix. Understanding this physics is what separates engineers from buyers.
Four ideas to carry into the next specification conversation you have.
P doped with electron-acceptors (holes). N doped with electron-donors. Forward bias drives them to the junction.
When electron drops into a hole, energy E = bandgap is released as a photon. λ = 1240 / E_eV nm. Blue chip has ~2.7 eV bandgap → 460 nm.
Yttrium Aluminium Garnet (YAG) phosphor absorbs blue, re-emits yellow-orange. Blue + yellow = white. Quality phosphors add red phosphor for high R9.
Higher Tj = less light, redder colour, shorter life. LM-79 measures at thermally stable Tj. Saudi designs must derate for ambient 35-45°C.
Which material makes which colour, and why white needs phosphor.
| Material | Bandgap (eV) | λ / colour |
|---|---|---|
| GaN | 3.4 | 365-400 nm UV |
| InGaN (low In) | 2.7-2.9 | 450-470 nm blue |
| InGaN (high In) | 2.4 | 520 nm green |
| AlGaInP | 2.0-2.1 | 590 nm amber |
| AlGaInP | 1.9 | 625 nm red |
| Blue + YAG phosphor | , | White (broadband) |
| Blue + YAG + KSF/Nitride | , | Warm white, high R9 |
Five engineering consequences of LED physics for your spec.
Blue chip → blue + yellow phosphor → white perceived. Each stage has Stokes losses. Total wall-plug efficacy: 50-60% real LED, 200+ lm/W.
GaN blue chip drops 0.1-0.3% per °C. Phosphor degrades 0.5%/°C. Combined: 25-40% lumen loss at Tj 100°C vs 25°C. Heatsink design matters.
YAG phosphor degrades over thousands of hours. Lamp shifts greenish-yellow with age (Duv goes positive). Premium fixtures use stable phosphors + KSF red for stable colour.
An LED rated 5000 lm at 25°C delivers ~4000 lm at 45°C ambient (Saudi summer recess). Always check the LM-82 thermal derating curve.
LED Vf drops 2-4 mV/°C. Constant-current drivers compensate; constant-voltage drivers over-drive cold LEDs. Saudi outdoor benefits from constant-current.
Every NLC LED is tested at 25/45/65°C ambient with LM-82 thermal data. KSF red phosphor for stable R9. Constant-current driver standard. Designed for Saudi heat.
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