Care Fundamentals
Grow lights for Lithops: PAR, DLI, and spectrum
What 'enough light' actually means for indoor Lithops, in numbers you can measure rather than rules of thumb that fall apart in winter.
Three numbers that matter
PAR (photosynthetically active radiation) measures the photon flux density actually usable by the plant, in µmol/m²/s. DLI (daily light integral) is PAR integrated over the photoperiod, in mol/m²/day. Spectrum is the wavelength mix the lamp emits.
Lithops in habitat receive a DLI of 35 to 50 mol/m²/day in summer. Indoor growers do not need to match that — most cultivated plants do well at 18 to 25 mol/m²/day, which corresponds roughly to 350–500 µmol/m²/s of PAR for 14 hours.
Practical setups
A modern 30 W full-spectrum LED bar at 25 cm above the canopy delivers about 400 µmol/m²/s on a 30 × 30 cm area. That is plenty for a single shelf of Lithops on a 14-hour timer.
A typical south-facing windowsill in winter at mid-latitude delivers a DLI of 4 to 8 mol/m²/day — well below the threshold for healthy growth. This is why etiolation is almost universal among indoor winter Lithops without supplemental light.
Spectrum and colour rendering
Full-spectrum white LEDs in the 3500 K to 5000 K range, with CRI above 90, are the right choice. They produce the broadband light the plant evolved under and they let you see the window colour accurately for diagnosis.
Pink/purple 'blurple' lamps work for growth but make every plant look the same colour. You lose the ability to spot the early stress signals you should be watching for.
How to verify
Buy or borrow a PAR meter once. Measure at canopy height in three or four spots, write the numbers down, and trust them. PAR drops with the inverse square of distance — moving the light from 20 cm to 30 cm above the plants halves your reading.
Frequently asked questions
- Will a regular desk lamp work?
- No. Even bright incandescent or low-end LED desk lamps deliver under 50 µmol/m²/s at canopy height. The light is also poor spectrum.
- How long should the photoperiod be?
- 12 to 14 hours in active growth seasons, 8 to 10 hours during the rest period. Mimic the natural day length of the habitat range rather than running 24 hours.
- Do I need to dim the lights in summer?
- Only if you are also getting strong window sun. The two add up and the canopy can easily exceed habitat DLI, which causes its own kind of stress.
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Written by the Editorial Team. Spotted an error or want to add a regional note? Send corrections or apply to contribute.