After three months under four controlled light levels, 12 species sorted themselves into three clear groups. Here's the cheat-sheet for where each one belongs on your shelf.
The experiment: 12 species · 4 intensity levels · ~3 months · Units: PPFD (µmol/m²/s)
If you only remember one thing from this whole experiment, make it this map. Plants don't simply want "bright" or "low" light — each wants a specific band of intensity, and missing it shows up fast: too little and they stretch and pale; too much and they scorch and shrink.
I plotted every species at the PPFD level where it grew best. Three zones jumped out:
Each large dot marks the PPFD level where a species did best; its color shows the light zone we'd put it in. Small open dots are the other levels tested.
The three light zones
| Zone | PPFD | Plants | What happens there |
|---|---|---|---|
| High light | 267–533 | Echeveria (both) | Compact, colorful growth; succulents tolerate the strongest light I tested and reward you for it. |
| Mid | 133–267 | Anthurium, butterwort | Want genuine light, but the top of this band is their ceiling — push higher and they stall. |
| Low light | 82–133 | Caladiums, alocasias, staghorn fern* | Understory jungle plants; best growth down here, visible damage above 267 PPFD. |
* The staghorn fern (one plant per level) gave mixed signals: its fronds grew longest at 533 PPFD, but it kept its spread and made the most spore fronds at 82. We've grouped it with the low-light plants; 82–133 PPFD is a sensible start.
How to use it on a shelf
Rack-layering cheat-sheet
- Top shelf / closest to the light (267–533 PPFD): succulents — Echeveria and friends.
- Middle shelf (133–267 PPFD): anthurium, butterwort.
- Bottom shelf or shaded edge (82–133 PPFD): caladiums, alocasias and the staghorn fern — keep the aroids out of the hot zone.
Two plants worth calling out
Anthurium is the generalist. One of the two hybrids kept growing at every level from 82 to 267 PPFD, and neither collapsed the way the caladiums did — if you have an awkward spot, an anthurium will probably take it. The variegated alocasia is the diva: with less chlorophyll to spare, it was only trialled up to 267 PPFD — and by mid-July the plants at 133 and 267 had died back, while the pair at 82 PPFD was still growing.
One caveat. These optima come from one full-spectrum light (red:blue about 3.2:1) run on a fixed daily schedule. Change the spectrum, the hours, or the season and the exact numbers shift. But the ranking — succulents high, aroids low — is rooted in where these plants evolved and holds up broadly.
More from this experiment
- Part 1 — The setup: 12 houseplants, 4 light levels
- Part 3 — Echeveria: compact rosettes and pink color
- 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 — high output for the top, sun-lovers' shelf, where Echeveria and other succulents want 267–533 PPFD.
- Barrina T5 10W magnetic grow lights — gentler, even light for the middle and lower shelves: anthurium, butterwort, caladiums and alocasias.
- Barrina Orbgrow 9W dimmable puck — for a single plant that doesn't fit its shelf's zone; dim it up or down to match.
