Light is the first thing to check when a carnivorous plant grows pale, stretched or stops making traps. Pick your plant, enter the reading from a lux meter or a PAR (PPFD) meter taken at leaf level, and add how many hours a day the light is on. The checker compares your numbers with the lighting guide of the International Carnivorous Plant Society (ICPS) and the PPFD ranges published by the nursery Carnivero, and works out your daily light integral (DLI).
How to Take a Reading
Hold the meter where the leaves are, facing the light. The ICPS guide uses lux, and notes that a lux meter measures light with the same sensitivity as the human eye. It also warns that there is no definitive way to measure exactly how much of a lamp’s light is useful to plants, so most of the time light levels come down to trial and error. The ICPS lux ranges are for white light, and it notes that meters marketed for plant lighting give a number that could be of little value. Carnivero publishes its ranges as PPFD (photosynthetic photon flux density, in µmol/m²/s), the reading a PAR meter gives.
Where the Numbers Come From
| Plant | ICPS rating (white light) | Carnivero PPFD (µmol/m²/s) |
|---|---|---|
| Venus flytrap (Dionaea) | Intense: about 15,000 to 25,000 lux | 100 to 400 |
| Sundews, most species (Drosera) | Intense | 100 to 500+ |
| Sarracenia | Intense (rated for seedlings) | Low-growing 100 to 400; upright 200 to 500+ |
| Heliamphora | Intense | 100 to 400 |
| Cephalotus | Intense | 45 to 300 |
| Darlingtonia | Not rated | 75 to 400 (estimate) |
| Nepenthes | Moderate: about 8,000 to 15,000 lux | 30 to 200 |
| Butterworts (Pinguicula), Mexican and temperate | Moderate | 30 to 200 |
For scale, the ICPS puts full noon sun at about 100,000 lux, bright shade at about 15,000 lux and typical office lighting at 1,000 lux. It says intense-light plants need the lights on for 12 to 16 hours a day, and that plants survive with less light but do not grow as well. Carnivero’s figures assume a 12 to 14 hour photoperiod; it suggests starting around the low-middle of each range and adjusting to how the plant responds, and notes that some ranges come from greenhouse experience rather than tests under lights.
What the Daily Light Integral Means
PPFD is how much light reaches the leaves each second; the daily light integral is the total over a day. The conversion published by Apogee Instruments multiplies PPFD by 3,600 seconds and divides by 1,000,000 to turn micromoles into moles, which gives 0.0036 mol/m² per hour of light. So DLI = PPFD × hours × 0.0036. Apogee notes this is accurate only under electric lights: sunlight changes through the day, so one reading by a window cannot give you a daily total.
Related Guides
- Nepenthes light requirements and grow lights
- Butterwort light requirements
- Venus flytrap care
- Sundew care
- Sarracenia care
- Temperature and humidity checker
Sources
- International Carnivorous Plant Society, LED plant lighting, John Brittnacher [carnivorousplants.org/grow/SoilsWaterLight/LEDplantlighting]
- International Carnivorous Plant Society, Heliamphora growing guide [carnivorousplants.org/grow/guides/Heliamphora]
- Carnivero, Genera specific PPFD recommendations [carnivero.com/pages/grow-light-ppfd-recommendations]
- Apogee Instruments via Hort Americas, Conversion: instantaneous PPFD to integrated PPFD [hortamericas.com/grower-resources/conversion-instantaneous-ppfd-to-integrated-ppfd]
This tool is editorially reviewed and its limits are checked against the cited sources. Last reviewed: October 2026.