How many lumens per watt does a high CRI LED strip produce?
Expect roughly 150-170 lm/W from an Ra 80 board, 120-140 lm/W from a blue-excited Ra 95 board and 80-110 lm/W from a violet-excited full spectrum board, all at 4000K and a nominal drive current. LED strip lumens per watt falls as CRI rises because the extra red phosphor absorbs and re-emits light that a low-CRI board simply lets through. Budget from target lux and diffuser transmittance, then check the resulting watts per metre against the project energy allowance before fixing the CRI grade.
Where the watts go
Two mechanisms set the ceiling. Stokes loss is the energy cost of converting a short-wavelength pump photon into a longer-wavelength emitted one, which is why a 405 nm pump inherently costs more than a 450 nm pump. Phosphor loading is the second: the deep-red emitters that lift R9 above 90 sit at the edge of the eye's sensitivity curve, so they consume power while contributing few lumens.
That is the honest trade behind every Ra 95+ claim. A board that reports Ra 95 at 160 lm/W has almost certainly been measured at low drive current or at a cool CCT with a thin red phosphor, and its R9 will confirm it.
Designing to a wattage budget
Size the scheme from lumens per metre, not watts per metre. A 14.4 W/m blue-pump board at 140 lm/W delivers about 2000 lm/m; matching that output on a violet-pump board needs roughly 20 W/m, which changes the copper weight, the feed spacing and possibly the profile. Running the numbers before the layout is fixed avoids a late redesign.
Where the energy class is declared, the ErP calculation uses the whole luminaire, so driver efficiency and profile transmittance matter as much as the tape. A 92% transmittance frosted diffuser costs less than the difference between the two excitation families.
Industry references and standards
- Energy & compliance — EU Regulation 2019/2020 (ErP for Light Sources) — Efficacy, flicker (Pst LM) and SVM limits that apply to strips sold in the EU.
- Energy & compliance — ENERGY STAR Lighting Program — North American efficacy and lumen-maintenance benchmarks.
- Engineering standards — IEC 62717 — LED Modules for General Lighting — Performance and lumen-maintenance requirements for LED modules.
More full spectrum answers
- What is the difference between a high CRI LED strip and a full spectrum LED strip?
- Is violet-excited high CRI LED lighting better than a normal blue-chip white LED?
- Is 90 CRI enough, or do you need a 95 or 98 CRI LED strip?
- Which high density LED strip stops you seeing dots in a shallow cove?
- Are high CRI LED strips available in 24V, and do they dim without changing colour?
- Can you use a full spectrum LED strip to grow plants?