Solar RGB versus Solar RGB II

Question

Does the Solar RGB II materially improve usable PAR distribution and edge coverage over the original fixture on a 90P?

Background

The original fixture produces strong center output while PPFD varies substantially across the tank, and raising it to widen the footprint costs more at the ends than it gives back. Whether a different fixture geometry produces a more even field across a 90 cm tank, and whether that matters to the plants at the outer positions, is a measurable question that no published figure currently answers.

Hypothesis

Three separate claims, kept apart on purpose. The retailer's: listings for the Solar RGB II quote up to 31,000 lux ± 10% at 30 cm, and give 30 cm above the water as the intended mounting distance. The figure of roughly 1.5 times brighter than the original circulates widely and is close to the ratio of the two published illuminance figures, but it does not trace to anything ADA publishes directly. ADA's own Solar RGB page lists LED count, wattage and color temperature without an illuminance figure at all, so treat 1.5× as a retail claim of uncertain provenance rather than a manufacturer specification. There is a second problem with it: lux is a point measurement weighted for the human eye, taken under the middle of the fixture. It is not PPFD, and it says nothing about what happens 45 cm to either side. A fixture could be half again as bright directly underneath and leave the ends of a 90 cm tank exactly where they are now. What was measured here: the constraint on this tank is coverage rather than peak output, and raising this particular fixture cost more at the ends than the wider footprint gave back. The prediction, which is neither of the above and is stated so it can be shown to be wrong: if a replacement starts with roughly 1.5 times the output, that surplus may be enough to cover the loss from hanging it higher and still leave the ends better off than they are now.

Recorded before measuring, so it can be shown to have been wrong.

Equipment

Method

Not run yet. The method is set out under Measurements below.

Measurements

• ·Planned: the II's dimmer setting recorded against every reading. The original has no dimming and therefore one output; the II does, so its setting is a variable that has to be stated or the comparison is not like-for-like
• ·Planned: a first pass with the II set as close to the original's output as it can be made, so geometry is compared rather than brightness
• ·Planned: PPFD at the same nineteen live positions for both fixtures
• ·Planned: center-to-edge ratio at a matched mounting height, compared against the standing survey; this is the first thing to measure, not peak PAR
• ·Planned: the same ratio again with the fixture raised to whatever height the extra output can afford
• ·Planned: how far it can be raised before the ends fall back to where they are today, which is the number that decides whether the extra output is worth anything on this tank
• ·Planned: substrate and canopy readings, since those diverge as stems fill in
• ·Planned: DLI derived from PPFD and photoperiod, so the two fixtures compare on daily light rather than instantaneous intensity

Observations

No observations yet. This experiment has not produced data.

Future work

• ·Obtain a Solar RGB II to test.
• ·Photograph the same scape under both fixtures at matched camera settings.
• ·Publish the result either way. If the ends end up higher than the standing survey while the center stays reasonable, it worked; if they do not, that is worth publishing too.

Related documentation