Sunlight and incandescent lamps emit smooth, continuous spectra across all visible wavelengths. Fluorescent, mercury vapour, and older LEDs emit spiky, discontinuous spectra with gaps. Two lamps can have the same CCT but completely different render quality. The trick: a continuous SPD makes red, green, blue all render naturally. Spiky SPD distorts colours unpredictably.
Four ideas to carry into the next specification conversation you have.
Black-body curve. All wavelengths present. Reference for all colour science.
Resistive heating = Planckian curve. Heavy in red and IR. CRI 100 by definition.
Mercury arc + phosphor coating. Specific peaks at 405, 436, 546 nm + phosphor bands. Gaps between.
Blue chip + multiple phosphors (YAG + KSF + red nitride) approximates continuous. Ra 95+, R9 ≥ 50.
How each technology shapes its SPD, and what that means for colour.
| Source | Spectrum | CRI / R9 |
|---|---|---|
| Sun (D65) | Continuous | 100 / 100 |
| Halogen | Continuous warm | 100 / 100 |
| Incandescent | Continuous warm | 100 / 100 |
| Mercury vapour HID | Spiky | 20-50 / very low |
| HPS sodium | Narrow yellow | 25 / negative |
| Fluorescent CFL | Spiky + phosphor | 70-85 / 0-30 |
| Cheap LED | Spiky blue + YAG | Ra 80 / R9 ~0 |
| Premium LED | Near-continuous | Ra 95 / R9 90 |
Five applications where spectrum shape changes the outcome.
Skin pigments reflect across the spectrum. Spiky SPD with red gap = grey skin. Continuous SPD = natural. Critical for hospitals and luxury hotels.
Hemoglobin red reflects 600-700 nm. SPD with low red = grey meat. Premium butcher LED has red-boosted continuous SPD.
Dyes reflect across hundreds of wavelengths. Spiky SPD distorts saturated colours. Brand-defining quality issue.
Pigments must render faithfully. ISO 3664 specifies D65 daylight or similar continuous SPD for art viewing. Spiky LED forbidden in conservation lighting.
Plants and algae need specific photosynthetic wavelengths (chlorophyll absorbs at 430/660 nm). Custom continuous + targeted-peak LED maximises growth.
Every premium NLC LED includes a printed SPD curve. We use KSF + nitride red phosphor for near-continuous spectrum. Verify continuous before you buy.
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