A ballast regulates the current reaching an HPS, MH or CDM lamp. Without one the lamp draws until it destroys itself, so this is not an optional component – it is the thing that makes the lamp work at all.
Digital, not magnetic
Old magnetic ballasts are heavy, run hot, buzz, waste power as heat and cannot be dimmed. Digital (electronic) ballasts are lighter, quieter, more efficient, and let you run the lamp at reduced output. There is no reason to buy magnetic now.
Why dimming matters more than people expect
Summer. Drop a 600W to 400W on a hot week and keep the crop rather than losing it to heat stress.
Early flower. Ease plants up to full power over a few days instead of shocking them.
Lamp life. Running at 75% extends lamp life considerably.
Super-lumen / boost. Most digital ballasts also over-drive slightly for the final weeks. Useful, but it shortens lamp life – use it deliberately, not permanently.
Matching ballast to lamp
Ballast
Lamp
Fitting
240V digital, 250-600W
Single-ended HPS or MH
E40
400V digital, 1000W DE
Double-ended HPS
K12x30
CDM / CMH ballast
315W ceramic
PGZ18
These are not interchangeable. A DE lamp on a standard 240V ballast will not run, and a single-ended lamp on a 400V ballast will fail. If unsure, tell us the lamp you have.
Placement
Ballasts get warm and are the heaviest part of a lighting setup. Mount outside the tent where possible – it keeps the heat out of the grow space and off the tent frame. Never sit one on the floor where run-off could reach it. See grow room electrical.
We are a hydroponics shop in Croydon. Tell us the lamp and reflector you already own and we will match the ballast rather than guessing. Discreet UK and European delivery, and excellent customer reviews on Trustpilot.
