Both succulents barely changed width over the summer — but that's not the story. The real signal is in their height and their color.
The experiment: 12 species · 4 intensity levels · ~3 months · Units: PPFD (µmol/m²/s)
If you're expecting dramatic before-and-after size photos, succulents will disappoint you: they're slow, and a summer indoors won't bulk up an Echeveria much. The interesting response to light isn't size — it's shape and color. And on both counts, more light won.
The same Echeveria rosettes on 14 May and 17 July under strong light: they held their width and flushed pink.
Echeveria 'Chihuahua' on 17 July, four light levels side by side. Left to right, as PPFD rises, the rosettes turn pinker.
Height is a compaction signal (and lower is better)
For a rosette succulent, plant height is really a stretch gauge. When light is too weak, the plant etiolates — the stem lengthens, leaves space out and angle upward as it reaches for more. When light is strong, the opposite happens: the rosette pulls in tight and flat. So a height line that drops under strong light is good news.
'Chihuahua' height over time. Every group tightened over the summer, but the 267 PPFD rosettes pulled in the most — from 1.77 to 1.17 cm — while holding their footprint. That's compaction, not decline.
'Amber' tells a similar story: all four groups tightened, with 133 and 267 PPFD finishing lowest.
The color payoff
Look again at the lineup photo. From about 267 PPFD up, the leaves flush pink and red — anthocyanin pigments the plant produces as mild sun-stress protection. It's the exact "stressed" coloration succulent growers chase, and it simply doesn't appear under low light, where the same plants stay blue-green.
What to actually do
Echeveria, practical settings
- Give them your strongest light — 267–533 PPFD is ideal (267 gave the tightest rosettes, 533 the deepest color).
- Don't expect fast growth; expect tight, colorful rosettes that hold their form.
- Low light (82 PPFD) keeps them alive, but they stay blue-green — the pink never shows. Over longer stretches, weak light is what makes a rosette stretch and open up.
Myth check: "succulents burn under indoor LEDs." Not these, not at these levels. Typical household grow-light intensities rarely approach real midday sun — for most indoor succulents the problem is far more often too little light than too much.
More from this experiment
- Part 1 — The setup: 12 houseplants, 4 light levels
- Part 2 — The brightness map: which plant goes where
- Part 4 — Caladiums and alocasias: the shade-lovers
- Part 5 — Butterwort and staghorn fern
- Part 6 — Five light colors on one dwarf tomato
Lighting we'd recommend
- Barrina T8 42W grow lights with reflectors — enough output to put a whole shelf of succulents into the 267–533 PPFD range; hang them close above the rosettes and check the PPFD chart on the product page.
- Barrina TX36 2 ft grow light — a compact, high-output bar for a small succulent shelf.
- Barrina Orbgrow 9W dimmable puck — concentrated light for one or two pots on a desk or windowsill; dimmable, so you can raise intensity gradually and avoid sunburn.
Slim, low-output tube lights suit foliage plants better than succulents: one 1 ft T5 delivers only about 140 PPFD even 10 cm away.
