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Project Notes

#471 Fluorescent Ring LED Replacement

Understanding fluorescent lighting and installing an LED replacement.

Build

Notes

My home has fluorescent lighting fixtures circa the late 1990s. The ballasts are starting to fail, and so I am gradually replacing the units with higher efficiency LED alternatives.

Typical Installation

Mostly I have circular ceiling units that are the problem. These use the preheating/switchstart system involving:

fluorescent_installation

How Fluorescent Lighting Works

In fluorescent lighting, an electric current excites low-pressure mercury vapor, producing short-wave ultraviolet light that causes a phosphor coating on the inside of the lamp to fluoresce.

The noble gas used in the tube (commonly argon) must be ionized before the arc can strike. Larger tubes require higher voltages for this (up to thousands of volts).

The starter is a very basic switching oscillator that can generate the required voltages in the ballast - in essence we have the basics of a switching boost converter. Once the arc has struck, the starter is bypassed and stops.

When in operation, the ballast acts as a governor for the tube, preventing the current draw from running away and blowing itself up.

fluorescent_installation

“EXPLAINED : Working of tubelight” by brain amplifier provides a very good explanation of the internals of this kind of system:

clip

LED Replacement

I found a 15W LED Ring PANEL Circle Light AC220V - 240V SMD 5730 LED Round Ceiling from a seller on aliexpress. These turned out to be a perfect replacement for the 30cm fluorescent rings with a diffuser cover.

The LED ring is 201mm in diameter, and has 15x 5730 LEDs in series, with each of the 15 serials stages containing 2 LEDs in parallel. Hence the model number: ø201mm-5730-2P15S!

kit_parts

Note: there are some LED ring units that connect directly to mains and do not need a separate driver unit (the driver is built-in to the LED board), such as the

alt_without_driver

LED Driver

The LED driver is a simple switching converter

kit_driver

kit_driver_rear

The driver follows a standard circuit recommended for the WS3441 high precision buck constant current LED driver. This is my re-drawing of the actual circuit:

Schematic

It uses an MB10 full bridge rectifier on the input.

Wiring Standards

In Singapore, the Cable Colour Code changed from 2009-03-01.

sg_wiring_code

My property is pre-2009, so I have:

  • blue: line
  • black: neutral
  • yellow-green: earth

Installation

The LED ring fits quite nicely in the same dome housing as the original 30cm circular fluorescent tube.

kit_installed

Credits and References

About LEAP#471 LEDPowerLighting

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

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About LEAP

LEAP is my personal collection of electronics projects - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting.

Projects are often inspired by things found wild on the net, or ideas from the many great electronics podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know or send a pull-request.

NOTE: For a while I included various scale modelling projects here too, but I've now split them off into a new repository: check out LittleModelArt if you are looking for these projects.

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