Every LED flat panel is one of two designs. Edge lit panels shine light in from the frame and spread it across a light guide plate. Backlit panels put the LEDs right behind the diffuser. They look almost the same in the box. They do not age the same in the ceiling.
The short version
| Edge lit panel | Backlit panel | |
|---|---|---|
| Where the LEDs sit | Around the inside of the frame | Across the back of the housing |
| How light spreads | Through an acrylic light guide plate | Straight through the diffuser |
| Depth | Very thin, often under 1 inch | A little deeper, still fits any drop ceiling |
| Efficiency | Good | Usually higher lumens per watt |
| Long term look | Light guide can yellow with age and heat | No light guide to yellow |
| Price | Often higher for the same output | Often lower |
How an edge lit panel works
A strip of LEDs runs around the inside edge of the frame and fires sideways into a sheet of acrylic called a light guide plate. Tiny dots etched into that sheet bounce the light down through the diffuser. That is what makes edge lit panels so thin, and why they became the classic "flat panel" look in offices.
The weak point is the light guide itself. Acrylic can yellow over the years, especially in warm plenums, and some light is lost every time it bounces. Cheap panels show it first as a warm, uneven tint near the edges.
How a backlit panel works
A backlit panel, sometimes written back-lit or called direct lit, spreads the LEDs across a board at the back of a shallow housing and lets them shine straight through a diffuser. Fewer parts in the light path means more of the light actually reaches the floor, and there is no light guide to discolor.
The trade off is depth. A backlit housing is deeper than an edge lit one, but in a standard lay-in T-bar grid that does not matter. It only matters in tight surface mount or very shallow plenum situations.
Which one should you buy?
- Standard drop ceiling, large quantity, budget matters. Backlit. Better efficiency and usually a lower price per fixture.
- Very shallow plenum or surface mount where depth is tight. Edge lit.
- Warm ceilings, kitchens, or anywhere you want the panels to look new in ten years. Backlit, because there is no acrylic light guide to yellow.
- You need to match existing panels already on the floor. Match what is there so the ceiling looks uniform.
Rebates do not care which one you pick. What matters for a utility rebate is the DLC listing on the installation date, not the design. Check the DLC badge on the product page either way.
Sizes and options
Both styles come in the three standard grid sizes: 2x2, 2x4 and 1x4. Most commercial panels now have field selectable wattage and color temperature, 0-10V dimming, and versions with an occupancy sensor or emergency battery backup built in. If you are still deciding between a panel and a troffer, read panels, troffers and center baskets.
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Backlit and edge lit panels in every grid size, at contractor pricing with freight quoted at real cost.
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