Every white light has the same job, but they get there with very different recipes. The SPD curve shows exactly how much power a lamp emits at each wavelength from 380 to 780 nm. It's the truth behind CCT and CRI. Two 4000 K lamps can look identical on paper and very different in real life.
Four ideas to carry into the next specification conversation you have.
X-axis: wavelength 380-780 nm. Y-axis: relative power. Every lamp has a unique SPD signature.
Sun has power at every visible wavelength. Incandescent and halogen are close. Best colour rendering.
Mercury, sodium, fluorescent show peaks and gaps. CRI suffers in the gaps.
Blue chip peak + yellow phosphor hump = phosphor-converted white. Red dip at 660 nm is why some LEDs render skin poorly.
What the curve looks like for each common Saudi lamp source.
| Lamp type | SPD character | Colour rendering |
|---|---|---|
| Daylight (D65) | Continuous smooth | Ra = 100 (reference) |
| Incandescent / halogen | Continuous, red-rich | Ra = 100 |
| Fluorescent T5/T8 (3-band) | Three sharp peaks | Ra = 80–85 |
| Low-pressure sodium | Monochromatic 589 nm | Ra ≈ 0 |
| High-pressure sodium | Broad orange band | Ra = 25 |
| Metal halide ceramic | Multi-line broad | Ra = 80–95 |
| LED phosphor white 3000K | Blue peak + yellow hump | Ra = 80–90, R9 low |
| LED premium violet-pumped | Smoother, red-rich | Ra = 95+, R9 = 90+ |
Five things the SPD shows that CCT and CRI hide.
Every phosphor-white LED has a sharp peak at ~445-465 nm, the blue chip. That peak is what suppresses melatonin at night. Hospitality fixtures intentionally reduce this peak; office fixtures keep it for daytime alertness.
Saudi hospitality buyers reject LEDs with a deep red dip at 660-700 nm because skin looks dead. The fix is red-phosphor blending or violet-pump architecture, visible only on the SPD, not on CRI Ra alone.
EP12 covered CRI R9 ≥ 50 as a premium spec. SPD shows where that R9 comes from: the curve must have meaningful power at 620–700 nm. No power = no R9.
589 and 589.6 nm. Almost no other wavelength. Police cars look amber. Roads look readable. Stars stay visible. The narrow SPD is the feature and the bug.
Melanopic-EDI (Equivalent Daylight Illuminance) is computed from the SPD × the eye's ipRGC sensitivity curve. Same lux, different SPD = different circadian impact. WELL Building L03 sets the threshold.
Every NLC LED ships with its measured SPD chart from an accredited lab (LM-79). Not just CCT and CRI, the actual curve so designers can verify circadian and skin-tone behaviour.
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