Adjust the Spectrum on Dimmable LED Grow Lights

What "adjust the spectrum" means on a listing

A dimmable LED grow light listing can carry two separate promises. Dimmable means the brightness of the whole fixture can be reduced. Adjusting the spectrum means changing the mix of wavelengths the fixture emits, which the grower does by controlling separate LED channels. A listing that says only dimmable does not promise spectrum control. A listing that names a VEG/BLOOM switch, a red channel, or dual channel dimming does. See fixed spectrum versus multi-channel for the difference.

On a multi-channel light, each channel drives one group of LEDs, for example a white channel and a red channel. The word ratio in a title or bullet means the share of the output that comes from each channel. The bullet list states which channels exist; the maker's manual states how to set the ratio. Compare single-channel versus dual-channel dimming to understand what a listing can state.

DesignLights, a lighting program that publishes horticultural lighting requirements, describes horticultural LEDs as able to deliver the right spectrum, intensity, and duration for different crops. That describes the product category; it is not a specification for a particular model. The specification for a model is read on the listing and the maker's page.

Growth stages as listing words

Plants require light for photosynthesis, as the University of Minnesota Extension explains, and a grow light exists to provide it. Many listings name growth stages such as seedlings, vegetative growth, and flowering as context for the channel settings. The listing states the stage words; the maker's page and manual state which channel setting the maker recommends for each stage. Read that pairing on the maker's page rather than guessing. The guide on flowering versus foliage explains how the words appear.

The purpose of a channel switch is to let the grower change the light mix without replacing the fixture. What the mix should be for each stage is an instruction the maker prints in the manual. This site reads only the stated details of the listing; it does not add a recipe. See full spectrum versus targeted wavelengths for how listings describe the two approaches.

Reading the channel words on a listing

Words such as VEG/BLOOM, full spectrum plus red, dual channel, or independent red and white dimmers are the listing terms that describe spectrum control. A wavelength name such as 660nm red is a description of the LEDs in that channel, not a measurement of the light output. The title names the feature; the bullet list names the controls. The difference between a white light and a so-called blurple light is covered in white LED versus blurple spectrum.

When a title names two light types, such as quantum board and panel, the channel words still work the same way: each channel is one group of LEDs. The coverage area in square feet is a separate listing word, and the manual explains how a chosen setting relates to that coverage. The basics of reading channel colors appear in blue light versus red light.

Dimmer knob, switch, remote, or app

The control shape is a listing word too. A dimmer knob usually changes the brightness of one channel. A fixture with two knobs lets a grower set two channels separately. A switch labeled VEG/BLOOM picks a preset. Remote and app controls appear on listings as words, and the manual describes how they connect. Compare knob versus remote versus app dimming.

Some listings say linear dimming and some say stepped dimming. Linear dimming means the brightness changes continuously over the knob range; stepped dimming means the fixture offers a fixed set of levels. The manual states the exact behavior of the model. See linear versus stepped dimming for how the words are used.

Where the numbers are stated

This catalog does not list PAR, PPFD, or DLI for any channel setting. Those terms describe light in the photosynthetic range: PAR is the range of wavelengths plants use, PPFD is the flow of that light over an area, and DLI is that flow summed over the day. Figures for each setting appear on the maker's page and in the manual. The relationship between the terms is explained in PAR versus PPFD versus lux.

A buyer who wants the figures for a chosen setting looks them up on the maker's product page. Makers such as VIVOSUN and GE Lighting publish product information on their sites. The DesignLights Horticultural QPL page also lists qualified horticultural fixtures and their performance claims, which a buyer can read alongside the maker's page.

What to check before you choose

For a first light, a dimmable fixture with one channel is often enough to start. For a tent with separate stages, a fixture with two channels or a stage switch offers more choice. The best dimmable LED grow lights guide groups picks by stated details, and the guides for quantum boards and strips cover those light types.

• Does the title name a channel or preset, such as VEG/BLOOM or 660nm red?
• Does the bullet list name the controls: knob, switch, remote, or app?
• Does the listing state a coverage area in square feet, or does it leave the area unstated?
• Does the maker's manual state which setting matches which growth stage?
• Follow the maker's manual and local electrical rules for setup, and read the maker's page for the figures this site does not state.

What to pick for your job

Questions

Can every dimmable LED grow light adjust its spectrum?

No. Dimming changes brightness; spectrum adjustment needs a fixture with separate channels or a mode switch. Read the listing words: dimmable alone does not promise spectrum control, while VEG/BLOOM or dual channel does.

What does a VEG/BLOOM switch do on a listing?

It selects between two preset channel combinations. The listing names the presets; the maker's manual states which preset is designed for which stage. This site only relays the listing term.

Where is the wavelength ratio printed?

On the listing's bullet list and on the maker's product page. The manual shows how to set the ratio on the fixture. Figures such as PPFD for a setting are on the maker's page, not in this catalog.

Is spectrum control the same as a timer?

No. A timer controls the on and off schedule; spectrum control changes the wavelengths while the light is on. A light can have both, and each appears as a separate listing word.

Can I set the spectrum with an app?

Some listings state app control. The manual and the maker's page describe the app setup. Check the listing's stated details and follow the maker's instructions.

Do channel settings affect the coverage area stated on the listing?

The listing states a coverage area in square feet. How a chosen setting relates to that coverage is described by the maker in the manual.