Controlled chamber experiment, 12 trays, 288 plants

Controlled experiment poster example

A controlled experiment poster has to show that one thing changed and everything else was held fixed. This A0 portrait example grows 288 lettuce plants in 12 trays under three LED spectra for five weeks in one chamber. From the same 0.8 g start, the red heavy spectrum ends at 118 g a plant against 96 g under balanced white, 23% more.

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The whole board

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AVU

Does the light recipe change the harvest? Lettuce grown for five weeks under three LED spectra in a controlled chamber

O. Fairbanks ¹, R. Matsuda ¹ ²

1 School of Plant Sciences, Ashcombe Vale University · 2 Controlled Environment Facility, Ashcombe Vale University

Before: seedlings at week 0

Indoor growers choose a light recipe once and live with it for years. We tested three LED spectra at the same light intensity so that colour was the only thing that changed: a balanced white, a red heavy recipe and a blue heavy recipe. On day 0, 288 butterhead lettuce seedlings of one cultivar, sown on the same day and grown under the same white light for 14 days, were sorted by mass and dealt into 12 trays of 24 so that every tray started alike. Mean fresh mass at transplant was 0.8 g in every tray, with tray means between 0.78 g and 0.82 g. Four trays went under each spectrum, placed by a random draw across the three shelf zones of one chamber, so that a warm or bright corner could not favour one recipe. Everything else was held fixed: the nutrient solution, the 16 hour day, 22 degrees by day and 18 by night, and the carbon dioxide level.

PROPOSED PROTOCOL

Treatments. Three LED spectra at the same intensity: balanced white, red heavy and blue heavy, 16 hours a day.

Units. 12 trays of 24 plants, 288 plants in all, 4 trays per spectrum. The tray is the unit of analysis.

Chamber. One controlled chamber at 22 and 18 degrees, fixed humidity, carbon dioxide and nutrient feed.

Measures. Fresh mass of 6 marked plants per tray every week; every plant weighed at harvest in week 5.

Analysis. One way analysis of variance on the 12 tray means, then each spectrum against white.

Figure 1. Mean fresh mass per plant, g, at weeks 3 and 5 from a 0.8 g start. Bars left to right: balanced white, red heavy, blue heavy.

Source: 12 trays, 288 plants, controlled chamber.

After: harvest at week 5

All 288 plants were harvested. Mean fresh mass per plant was 96 g under balanced white, 118 g under red heavy and 104 g under blue heavy, from the same 0.8 g start. Red heavy beat white by 22 g, or 23%, 95% CI 14 to 30 g, and blue heavy by 8 g, or 8%, an interval that crossed zero. The red heavy trays led from week 1 and the gap widened every week after: 0.9 g at week 1, 3 g at week 2, 7 g at week 3, 14 g at week 4 and 22 g at harvest. Tray means within a spectrum sat within 6 g of each other.

REFERENCES

1.Delacroix, M. and Oyelaran, F. (2023) Red to blue ratio and leafy green yield indoors. Journal of Controlled Environment Horticulture, 17(2), 95 to 113.

2.Matsuda, R. (2024) Tray as the unit in chamber experiments. Plant Experiment Design Notes, 5(1), 12 to 25.

3.Fairbanks, O. (2025) Light recipes for butterhead lettuce. Ashcombe Vale Horticulture Report 8, 2025.

23% more

fresh mass under the red heavy spectrum

118 g against 96 g under balanced white at week 5; 4 trays each, 95% CI 14 to 30 g

Leaf count and colour

Leaf count and colour at harvest, mean per plant. Balanced white: 14.2 leaves, colour score 3.6 of 5. Red heavy: 15.8 leaves, colour score 3.1. Blue heavy: 14.9 leaves, colour score 4.3. The colour score is a trained panel rating where 5 is the deepest green. The red heavy recipe grew the most mass and the most leaves, but its heads were paler, and pale heads sell for less in a supermarket bag. The blue heavy recipe gave the deepest green with a mass that was not clearly different from white. So the choice depends on the buyer: a grower paid by weight would choose red heavy, and one paid on appearance blue heavy. One chamber and one cultivar limit the result: another lettuce, or a chamber with different air flow, could rank the spectra differently. Each spectrum had four trays, so the tray to tray spread, within 6 g, is the real measure of noise.

Key finding

Changing only the light colour moved the harvest by 22 g a plant.

Red heavy 118 g, blue heavy 104 g, balanced white 96 g

Red heavy 23% heavier than white, 95% CI 14 to 30 g

Red heavy heads were paler, colour score 3.1 of 5

Blue heavy gave the deepest green, score 4.3 of 5

Block by block

What each block on the board is for, in the order a reader walks it.

Title band and two authors: The title asks whether the light recipe changes the harvest. Two authors from the fictional Ashcombe Vale University.
Before: seedlings at week 0: The before panel says how 288 seedlings were dealt into 12 trays so every tray started at 0.8 g, and what was held fixed.
Protocol: Five entries: treatments, the tray as the unit, the chamber, what was weighed and when, and the analysis. This design prints PROPOSED PROTOCOL as the heading over a finished experiment, and the heading cannot be changed.
Figure 1 and after: harvest at week 5: Bars compare the three spectra at weeks 3 and 5. The after panel gives final mass, the 22 g difference with its interval and the gap by week.
Key number and leaf count and colour: The stat block gives 23% more. The leaf count and colour table from the row is written as three entries in the next section, followed by what the trade off means for a grower.
References, key finding and takeaways: Three references, a one line callout and four checked takeaways close the board.

What makes this board work

The unit is the tray, and it says so

288 plants sound like a large sample, but the spectra were applied to trays, so the analysis uses 12 tray means, 4 per spectrum. Stating the unit stops a reviewer asking whether plants were treated as independent.

Before and after carry the design

The before panel shows the start was equal: 0.8 g, tray means 0.78 to 0.82 g. The after panel then needs no baseline caveat, because the 96, 118 and 104 g at harvest all grew from the same start.

The winner has a cost

Red heavy grew the most mass and the most leaves, but its heads scored 3.1 of 5 for colour against 4.3 for blue heavy. Putting the trade off on the board turns a ranking into a decision.

Questions people ask

What should a controlled experiment poster say about controls?

Which variable changed, which were held fixed and how, and how units were assigned. This board holds intensity, day length, temperature, carbon dioxide and nutrients fixed, deals seedlings into trays by mass and places trays by random draw across three shelf zones. That one paragraph is what makes the comparison fair.

Why plot weeks 3 and 5 instead of every week?

Six weeks with three bars each put a tick label under the chart legend on this layout. Two weeks still show the gap growing, from 7 g at week 3 to 22 g at harvest, and the full weekly gap, 0.9, 3, 7, 14 and 22 g, is in the after panel.

How do I report a result whose interval crosses zero?

Give it plainly, with its size. Blue heavy beat white by 8 g, or 8%, and the board says the interval crossed zero, so the two are not clearly different on mass. Leaving it out would hide the colour result that makes blue heavy interesting.

Why does the methods block say proposed protocol?

The before and after design prints that heading on its method block and it cannot be set from the content, so it reads PROPOSED PROTOCOL over a finished experiment. For a planned study it fits. For completed work, choose another layout or tell readers that the five entries describe what was done.

How many replicates should a chamber experiment poster show?

State the replicate at the level the treatment was applied. Here that is 4 trays per spectrum, 12 in all, with 24 plants per tray. Add the spread between replicates, within 6 g here, so a reader can judge the 22 g difference against real noise.

Why put a colour score on a growth experiment poster?

Because mass is not the only thing a buyer pays for. The red heavy recipe won on mass, 118 g, but its heads scored 3.1 of 5 for green depth against 4.3 under blue heavy. Reporting the second outcome keeps the board honest about the trade off a grower would face.

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Sources

Written and checked by the OneCraft team. Last checked 4 October 2026.