Troffers and flat panels are the workhorses of commercial ceilings. They light offices, schools, clinics, and back-of-house spaces by the thousands, which means a good buying decision pays off across a whole building. This guide walks through the formats, settles the backlit versus edge-lit question, and lays out the specs that actually decide value.
Troffer, flat panel, or retrofit kit?
A troffer is a recessed fixture that drops into a modular ceiling grid. The three standard grid sizes are 2 foot by 4 foot, 2 foot by 2 foot, and 1 foot by 4 foot. Troffers usually sit recessed above the grid, though surface-mount versions exist for ceilings without a plenum.
A flat panel is a slim LED fixture that drops into the same grid sizes. Panels come in two constructions, edge-lit and backlit, which we compare below.
A retrofit kit converts an existing fluorescent troffer to LED without replacing the housing. Kits range from full door-and-lens assemblies to magnetic LED strips that mount inside the old fixture. Retrofits save on labor and disposal when the housings are in good shape, which is why the Department of Energy publishes a dedicated troffer retrofit guide.
Backlit vs edge-lit panels
The two panel types put the LEDs in different places, and that drives the trade-offs.
| Edge-lit | Backlit | |
|---|---|---|
| LED placement | Along the panel edges, firing into a light guide plate that spreads the light across the face | Across the back of the panel, firing down through a diffuser |
| Profile | Slimmer | Thicker, often around twice the depth of an edge-lit panel |
| Light spread | Light guide plate helps limit bright spots | Even output across the face |
| Aging | Acrylic light guide plates can yellow over time | Less prone to that yellowing |
| Efficiency | Long the assumed efficiency leader | Modern designs often match or beat edge-lit using fewer LEDs |
The short version: edge-lit wins on thinness, and modern backlit designs have closed the efficiency gap and often pull ahead while giving very even output. The performance difference between good examples of each is narrower than it used to be, so the best move on a large order is to compare a sample of each in the actual ceiling before you commit.
The specs that decide it
Efficacy (lumens per watt)
Efficacy is light out per watt in, and it drives the energy bill for the life of the fixture. As a benchmark, the federal FEMP purchasing program points buyers toward roughly 123 lumens per watt on a 2x2 troffer, 140 on a 2x4, and 120 on a 1x4. Treat those as a floor to shop above, not a ceiling.
Color temperature and selectable CCT
The common commercial color temperatures are 3500K, 4000K, and 5000K. Warmer 3000K suits hospitality and retail, neutral 4000K suits general offices, and cooler 5000K suits warehouse and industrial work. Many fixtures are now field-selectable: a small switch sets the color temperature at install, so one product covers several jobs and you stock fewer SKUs.
CRI: 80 or 90
Color Rendering Index rates how accurately a light shows color against a reference at the same color temperature. 80 CRI is fine for general offices, circulation, and warehouses. Step up to 90 CRI in color-critical spaces such as retail displays, where products need to look true, and in clinical settings where color judgment matters. Higher CRI usually costs some efficacy, so many designers use 90 in focal areas and 80 elsewhere.
Dimming and controls
0-10V dimming is the commercial standard and is built into nearly every commercial LED fixture made in the last several years. It is simple to wire and dims smoothly. DALI adds digital, addressable control for larger or more complex systems at a higher cost. One thing to keep straight: a wattage-selectable or lumen-selectable switch sets the output once at install and is not the same as dimming. For the full picture on dimming methods, see our guide to 0-10V dimming.
Glare in offices
In spaces full of screens, glare control matters as much as brightness. Unified Glare Rating puts a number on direct glare, and open offices with computer work typically target UGR 19 or lower. Lensed and low-glare optics help panels and troffers hit that target without dimming the room.
DLC listing and rebates
The DesignLights Consortium keeps a Qualified Products List of high-performing commercial lighting, and hundreds of utility rebate programs require a product to be on that list before it qualifies for an incentive. Some utilities pay more for DLC Premium products, which meet higher efficacy and lumen-maintenance bars, than for DLC Standard. If a rebate is part of your budget, confirm the fixture's DLC status and check your utility's program before you order.
Location and mounting
Most troffers and panels are dry-location fixtures for normal indoor spaces. For covered exterior soffits or areas with occasional moisture, choose a damp-location rating, and for anywhere exposed to direct water, a wet-location rating. Mounting options cover recessed lay-in for a grid ceiling, surface-mount boxes for hard ceilings, and suspended kits for open plenums.
Quick guidance by space
- General office: 2x4 backlit panel or troffer, 4000K, 80 CRI, 0-10V dimming, UGR 19 or lower, DLC listed.
- Retail or display: 90 CRI, 3500K to 4000K, and consider selectable CCT to tune the look.
- Warehouse or back-of-house: 5000K, 80 CRI, high efficacy, and look at high bays for taller ceilings.
- Retrofit: match the kit to your existing grid size and confirm DLC listing for the rebate.
Browse our troffers and LED flat panels, the wider interior lighting and lighting controls ranges, or the full commercial LED light fixtures collection. Not sure what specs to compare? Our guide to reading a lighting spec sheet breaks down the numbers.
Frequently asked questions
What is the difference between a troffer and a flat panel?
A troffer is a recessed fixture that drops into a ceiling grid in a 2x4, 2x2, or 1x4 size. A flat panel is a slim edge-lit or backlit LED fixture that drops into the same grid. Both are common in offices, schools, and healthcare.
Is backlit or edge-lit better?
Edge-lit is slimmer and fires its LEDs into a light guide plate. Backlit places LEDs across the back for very even output and, in modern designs, often equal or better efficiency. Compare a sample of each in your actual ceiling before committing on a large order.
What efficacy should a commercial troffer have?
As a benchmark, the federal FEMP purchasing program points to roughly 123 lumens per watt on a 2x2, 140 on a 2x4, and 120 on a 1x4. Higher efficacy means lower energy use for the same amount of light.
Do I need 80 or 90 CRI?
80 CRI is fine for general offices and warehouses. Choose 90 CRI for color-critical spaces such as retail displays and clinical areas, where colors need to look accurate. Higher CRI usually costs some efficacy.
What dimming do commercial panels use?
0-10V is the commercial standard and is built into almost every commercial LED fixture. DALI adds digital, addressable control for larger systems. A wattage-selectable switch sets output at install and is not the same as dimming.
Does the fixture need to be DLC listed?
For most commercial utility rebates, yes. The DesignLights Consortium Qualified Products List is required by hundreds of utility programs, and some pay more for DLC Premium than Standard. Check your utility's program before buying.
Lighting a full floor or a whole building? Request a quote or contact us and we can match troffers and panels to your layout and rebate. New to Rock? Create a contractor account for pricing.
This guide is general information. Product performance and rebate eligibility vary by manufacturer, model, and utility program. Confirm current specifications and DLC status on the manufacturer spec sheet and with your utility before purchase.