What belongs in an indoor grow-light specification?
How can a grower compare fixtures without losing sight of the light delivered to the crop and the electricity used by the facility?
Scope of this review
A targeted review of university lighting guidance, product qualification requirements and a primary paper on far-red photons. The intended output is a procurement and commissioning brief. No light fixtures were tested by Hamfy for this review.
How we assessed the evidence
We separated four evidence questions: metric definitions, daily dose, spatial distribution and wavelength coverage. We recalculated the two DLI examples from their stated inputs, then developed a proposed acceptance record. We did not rank manufacturers or estimate a crop’s return on investment.
What the evidence supports
Dose can be checked independently
The MSU guide supports the DLI calculation. Our two schedules both produce 14.4 mol/m²/day arithmetically. The comparison is deliberately limited to dose and makes no claim that the crops would respond equally.
Fixture performance and canopy delivery are different levels
The DLC requirements address product characteristics; MSU’s uniformity guide addresses light at the crop. Our proposed handover record joins those levels with a defined measurement plane, grid and operating setting.
The photon range belongs beside the metric
The far-red experiment is a reason to check spectral definitions carefully. For purchasing, our conclusion is to compare metrics on an identical wavelength basis and assess any different spectrum against evidence relevant to the proposed crop.
What this review does not establish
- No spectral programme, PPFD target or photoperiod in the worked example is recommended for a specific crop.
- Predicted distribution depends on geometry and assumptions that must be checked in the installed room.
- A lighting electricity calculation is not a whole-facility energy model or a measured production-cost outcome.
Hamfy’s proposed next step
Request a fixture test record, spectrum information, predicted canopy map and input-power schedule. Agree on the installed measurement grid before procurement. Connect those documents to the electrical and HVAC design, then retain the measured commissioning map as the reference for later changes.
Evidence to collect for a real project
- Crop and stage-specific light targets with the measurement wavelength range.
- Installed geometry and a defined canopy measurement plane.
- Fixture input power and spectral data at the intended operating settings.
- A commissioning light map and a complete production-period energy record.
Source notes
- University technical guide · 2021Indoor Lighting GuideMichigan State University
Source for conventional PPFD and DLI definitions and the constant-light dose calculation.
- University technical guide · Accessed 2026Urban Agriculture: Light Intensity and UniformityMichigan State University
Informs the distinction between average light level and distribution across the crop.
- Product qualification requirements · Version 4.0 · 2025Horticultural Lighting Technical RequirementsDesignLights Consortium
Reference for tested fixture metrics. This voluntary programme is not described here as a European legal requirement.
- Peer-reviewed experiment · 2020Far-red substitution, canopy quantum yield and photon capture in lettuceZhen & Bugbee · Frontiers in Plant Science
Supports checking wavelength definitions and the context of far-red findings. It does not supply a universal lighting recipe.