How to Read a Lighting Spec Sheet: The Numbers That Actually Matter

A lighting spec sheet (or "cut sheet") packs a fixture's whole performance story onto one or two pages. If you know which numbers to read, you can compare two fixtures in under a minute and avoid the classic mistakes: a "bright" light that renders colors badly, an efficient fixture with the wrong beam spread, or a part that won't meet code. Here's what each spec means and how to use it.

Lumens: how much light

Lumens measure the total visible light a fixture produces. More lumens means more light output. This is the number to compare for brightness, not wattage. Two fixtures can both draw 40 watts and put out very different lumens.

Quick rule: when someone asks "how bright is it," they mean lumens.

Watts: how much power

Watts measure power drawn, not brightness. With LED, watts only tell you operating cost and circuit load, not how much light you get. Don't shop by wattage the way people did with incandescent. Use it for load calculations and energy budgeting.

Efficacy (lumens per watt): the efficiency number

Efficacy, written as lumens per watt (lm/W), is lumens divided by watts. It's the single best measure of how efficiently a fixture turns electricity into light. Higher is better. Modern commercial LED fixtures commonly fall in roughly the 80-150 lm/W range; higher efficacy lowers operating cost and helps with energy-code compliance. When two fixtures hit the same lumens, the one with higher lm/W costs less to run.

CCT (color temperature): warm vs cool

Correlated Color Temperature (CCT), measured in Kelvin (K), describes the color tone of the white light:

• 2700K-3000K: warm, slightly yellow. Hospitality, residential, lobbies.
• 3500K-4000K: neutral white. Offices, retail, common areas.
• 4000K-5000K: cool, crisp white. Task areas, warehouses, garages, exteriors.

Lower Kelvin is warmer; higher Kelvin is cooler. Keep CCT consistent across a space so fixtures don't visibly mismatch. Many products are now offered as field-selectable CCT, so check whether the spec lists a single value or a switch-selectable range.

CRI (color rendering): how true colors look

Color Rendering Index (CRI) measures how accurately a light shows colors compared with a reference source, on a scale up to 100. Higher CRI means truer colors. As a rule of thumb, 80+ CRI is the common baseline for commercial and office spaces, and 90+ CRI is preferred where color accuracy matters, such as retail, healthcare, and display lighting. CRI is independent of brightness and color temperature; a bright fixture can still render colors poorly.

For more demanding color work, some spec sheets also list R9 (how well deep reds render) or TM-30 metrics (Rf/Rg), which give a fuller picture than CRI alone.

Beam angle: how the light spreads

Beam angle describes how wide the light spreads from the fixture, in degrees:

• Narrow (under ~60°): concentrated light for accent, spot, or high-mounting applications.
• Wide (~90° and above): broad, even coverage for general area lighting.

Beam angle matters most for downlights, floods, high bays, and accent fixtures, where the same lumens spread narrow vs wide changes the footcandles on the floor completely.

Power factor and THD: the "clean power" specs

Power factor (PF) measures how effectively the fixture uses the current it draws, from 0 to 1. Commercial specs and utility rebates often require PF of 0.90 or higher. Total Harmonic Distortion (THD) measures electrical "noise" the driver puts back on the line; lower is better. These matter most on large installs and for rebate eligibility.

Voltage and dimming: compatibility specs

• Input voltage: confirm the fixture matches the circuit (e.g., 120V, 277V, or a universal 120-277V range; 347V for some Canadian/commercial work).
• Dimming: check the dimming protocol the spec lists, such as 0-10V, ELV, TRIAC/phase, or DALI, and match it to your control system. A 0-10V fixture won't dim correctly on a phase dimmer. (See our explainer on 0-10V dimming.)

Lifespan, warranty, and ratings

• L70 / rated life: hours until the LED is expected to fade to 70% of initial output (e.g., L70 at 50,000 hours). It's a depreciation estimate, not a hard burnout point.
• Warranty: typical commercial LED warranties run about 5 to 10 years; confirm the term per product.
• Ratings and listings: look for UL/cUL or ETL listing, the IP rating for wet/dusty locations (e.g., IP65 outdoors), DLC listing if you need utility rebates, and wet/damp location labeling for exterior or covered fixtures.

A fast way to compare two fixtures

1. Lumens - is it bright enough?
2. Efficacy (lm/W) - which is more efficient at that brightness?
3. CCT - right color tone, and consistent with the rest of the space?
4. CRI (and R9 if it matters) - will colors look right?
5. Beam angle - does the light land where you need it?
6. Voltage + dimming - does it match the circuit and controls?
7. Listings (UL, DLC, IP, wet location) - does it meet code, rebate, and environment needs?

Run those seven in order and you've evaluated almost any fixture.

Need help reading a spec or matching a fixture?

Rock Lighting & Electric stocks commercial and outdoor LED from authorized brands, with contractor pricing and nationwide shipping. If you've got a spec sheet and want an equivalent that holds the same lumens, CCT, CRI, and listings at a better price, send it over. Browse RAB Lighting, see our RAB LED wall pack buying guide for spec-reading in action, or contact us with the cut sheet.

FAQ

Typical value ranges above are general industry rules of thumb, not the rating of any specific product. Always confirm the actual figures on the manufacturer's current spec sheet for the fixture you're buying.