Ingredient
PAR / light sensor
Also known as: photosynthetically active radiation sensor, BH1750, TSL2591, Apogee SQ-500
Sensor that measures light intensity in the wavelengths plants use for photosynthesis (PAR, 400–700 nm). The right ingredient when light is the limiting variable — supplemental greenhouse lighting decisions, indoor grow rooms, vertical farms, daylight-integrated DLI tracking. Two classes: lux meters (BH1750 ~$2, TSL2591 ~$5 — measure visible-light intensity, approximate PAR) and quantum sensors (Apogee SQ-500 ~$300+ — calibrated PAR in µmol·m⁻²·s⁻¹). Hobbyist DLI tracking is fine with lux sensors; commercial grow operations need quantum sensors.
Inputs / outputs
- Power: 3.3V or 5V, ~1 mA (lux sensors) or ~10 mA (quantum)
- Interface: I²C (lux sensors) or analog/SDI-12 (quantum)
- Range: BH1750 0–65,535 lux; TSL2591 0–88,000 lux; quantum 0–4000 µmol·m⁻²·s⁻¹
- Spectrum: lux sensors photometric (eye-weighted); quantum sensors PAR-flat
Solves / unlocks
- Daily Light Integral (DLI) tracking — sum of PAR over the day, the crop-yield-determining metric
- Supplemental lighting decisions (turn on grow lights when DLI is below crop target)
- Greenhouse shading control (close shade cloth above PAR threshold)
- [[vertical-farming|Vertical farm]] light-recipe optimization
- Plant-stress detection (sudden DLI drop from cloud or canopy issue)
Constraints
- Lux is not PAR — lux is human-eye weighted, PAR is plant-photosynthesis weighted; conversion factors are crop- and lamp-spectrum-dependent.
- Saturation — direct sun easily exceeds BH1750’s 65k-lux range; pick TSL2591 (88k) or use an optical filter.
- Quantum-sensor cost — for serious work, Apogee SQ-500 ($300+) is the standard; sub-$50 PAR sensors are unreliable.
- Mounting orientation — sensor must be horizontal at canopy height for valid measurements.
Source
- BH1750 (cheap lux): https://www.adafruit.com/product/4681
- TSL2591 (better lux): https://www.adafruit.com/product/1980
- Apogee SQ-500 (PAR quantum): https://www.apogeeinstruments.com/sq-500-full-spectrum-quantum-sensor/
See also
Auto-generated from this entry’s typed relations: frontmatter, grouped by relation type so the editorial signal isn’t flattened.
- Member of: [[ingredient]]
- Combines with: [[arduino-uno]] · [[esp32]] · [[bme280-environmental-sensor]] · [[home-assistant]]
What links here, and how
Inbound connections from across the wiki, grouped by lens and by relationship. These appear automatically — every entity page declares what it links to, and that data populates here on the targets.
Scientific
parallels
- Light as a working substrate the technology for measuring light as a budget — the PAR/DLI metric makes light a tracked resource
Practical
contains
- Farm-tech toolkit sensor / photosynthetically-active-radiation light sensor
combines
- Recipe: closed-loop greenhouse climate controller DLI tracking — the supplemental-lighting decision variable
3 inbound links · 5 outbound