BIOS Lighting – Dimming Control

When it comes to dimming control systems, our engineers know the importance of quality components and device adaptability.


All BIOS Icarus Horticultural LED fixtures come with two dimming control wires, which are accessible.  (Please refer to the table at the end of this article for wire colors)

The light level emitted from the fixture is proportional to the voltage on these dimming control wires.  Roughly, 10V = 100% output, 5V = 50% output, etc.

Any off-the-shelf light dimming control that says it supports 0-10V dimming control will work with BIOS Icarus Horticultural LED Lights.  Below are three off-the-shelf dimmers tested and recommended by BIOS.

Number of Fixtures for Each Dimmer

The maximum number of fixtures that can be connected to one dimmer depends on how much current the dimmer is capable of dissipating.

Each fixture connected to a dimmer sources the current used for dimming at a constant current between 2uA and 2mA (the amount depends on the driver or ballast).  This is known as ‘sinking’ the current. To account for cabling distances and accompanying voltage drops, BIOS always recommends running the calculations conservatively using 2mA for these calculations.

Add too many fixtures, and the amount of current on the circuit can exceed what the dimmer is capable of ‘sinking’, which will likely blow a fuse inside the dimmer.

Maximum current for three dimmer manufacturers, and the corresponding number of BIOS LED fixtures that can be connected per dimmer.

Dimming vs. Other Controls

When growers connect an off-the-shelf dimmer (see three examples above) to an Icarus fixture, they may notice the dimmer is not powered.  This is because BIOS follows industry standards for electronic ballasts (IEC 60929 annex E) which has the dimmer ‘sink’ the current which is ‘sourced’ by the ballast.  However, this is opposite of most control circuits.

Most industrial control systems (ie. HVAC, air handlers) ‘source’ the current instead of ‘sink’ the current.  The reason industry standards ‘sink’ has to do with reducing flicker and electrical noise prevention.

This can be an issue if the grow facility wants to use their industrial controllers, or PLCs, to also dim their LED fixtures.  In the past, BIOS provided instructions on building an adapter.  Soon BIOS will have a small interface box that can be installed in an instrumentation cabinet that will easily handle this conversion.

Elegant Control: “dim to off”

Powering LEDs from off to on is hard on the system because of an inrush of current to the circuits and relays.  This is why the dimming controls on all BIOS fixtures support “dim-to-off,” meaning that setting the dimming control voltage to something below 0.8V actually shuts off the output to the LEDs.  The supply then remains powered, but in a very low power sleep state until the dimming control voltage is again brought up above 0.8V.

This is an elegant control mechanism that eliminates the need for relay banks on light circuits, and avoids potential in-rush current problems caused from repeatedly turning on/off large numbers of super-efficient LED drivers simultaneously.

Digital and Wireless LED drivers

BIOS has always been on the cutting-edge.  Recently, BIOS has integrated Urban-Gro’s Soleil wireless controls into the Icarus Gi2 and Vi fixtures, giving BIOS customers the option to use digital, wireless control systems.

Wiring Table

From the beginning, BIOS Lighting has put their focus into research and building high quality, durable products.

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