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Start at leaf level

Houseplant light level & DLI calculator.

Use your own readings. Convert lux and foot-candles, calculate daily exposure from measured PPFD, or combine several light periods. Window direction and distance alone cannot determine brightness.

Light sensor at leaf height beneath a grow light.
AI-generated botanical illustration.

1. Enter a meter reading

Use a suitable meter at leaf level. An empty field is not a zero reading. A lux meter does not directly measure PPFD.

2. Read the calculation

Illuminance conversion
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PPFD (μmol/m²/s)
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Daily Light Integral (DLI)
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Enter your measured reading.

This DLI calculation assumes the PPFD stays constant for the entered hours. It does not rate a location as safe or suitable for a species.

Changing light through the day

For changing daylight, divide the observed day into separate periods. Enter an average PPFD for each period and its duration. Do not repeat one midday reading across the whole day. Leave unused rows empty.

Light period 1
Light period 2
Light period 3

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Add non-overlapping periods only, totaling no more than 24 hours. This estimates exposure for the periods you entered; it is not a full-day measurement unless they cover your actual light day.

Worked example: measured light

Example inputs, not a Doofer growing experiment: a steady PPFD of 200 for 8 hours gives 5.76 mol/m²/day. Two observed periods, 100 for 4 hours and 300 for 4 hours, also give 5.76. Equal totals do not prove equal plant responses.

The calculation is PPFD × hours × 0.0036. For several periods, add those products. Lux and foot-candles convert with 1 FC = 10.764 lux; converting either to PPFD requires information about the light spectrum, so this tool does not invent that conversion.

Compare two real locations

  1. Record the date, weather, meter, leaf height, and whether curtains or lamps are in use.
  2. Measure both locations with the same sensor orientation at comparable times.
  3. Repeat on another day before treating a difference as typical. Check the identified species before moving the plant.
Indoor Plant Lighting Guide
Common questions

Frequently Asked Questions

Answers to common questions about plant care and this tool.

Foot-candles and Lux measure illuminance based on human eye sensitivity (peaking at ~555 nm green light). PPFD (Photosynthetic Photon Flux Density, measured in μmol/m²/s) counts actual photons within the 400–700 nm Photosynthetically Active Radiation (PAR) spectrum that plant chlorophyll pigments can use for photosynthesis.

Daily Light Integral (DLI) adds up the photosynthetic photons reaching one square meter over a day, measured in mol/m²/day. It depends on intensity and duration: moderate light for 14 hours can give the same DLI as stronger light for 6 hours.

Follow the fixture manufacturer’s recommended distance and measure light at leaf height. Output, beam shape, and heat vary between lamps. Move plants gradually when increasing light and check for bleaching or scorch.

A windowless room needs suitable artificial lighting. Low-light plants still need light for photosynthesis. Watch for weak, stretched growth and adjust the lamp output and daily schedule to the plant’s needs.

Further reading and references

  1. Lighting for indoor plants and starting seeds — University of Minnesota Extension Guidance on light availability and supplemental lighting. Doofer’s examples demonstrate arithmetic, not measured plant outcomes. [Source ]