Dưới 20W LED lighting

Wattage is the power a fitting draws, not the light it gives. They are different numbers, and confusing them is the most expensive mistake in a retrofit. Brightness is measured in lumens; to judge whether a fitting is worth its price, look at lumens per watt rather than watts alone.

The most common error is a like-for-like swap: removing a 250W discharge lamp and fitting a 250W LED to be safe. In practice a 100W LED typically replaces a 250–400W discharge lamp. The correct method runs the other way: start from the light level the space needs, work from area and mounting height, then divide into fixture count and wattage per fixture.

Over-specifying is not the safe option. It wastes energy for the whole life of the installation, and under low ceilings it causes glare — staff sitting beneath it all day get tired eyes even though the space is over-lit on paper. Brighter than necessary does not make work easier; light in the right place does.