Luminaires, Lamps, Ballasts, and Drivers
Domain 3 - Luminaires, Lamps, Ballasts, and Drivers
This domain tests component-level knowledge: LED versus HID sources, ballasts and drivers, optical distributions, environmental ratings, and how component performance changes delivered light over life. Questions often hinge on what a datasheet value does and does not include.
Core rules
- LED luminaires use drivers that regulate current; HID uses ballasts (magnetic or electronic). Ballast factor (BF) multiplies lamp lumens; driver output current and forward voltage determine LED power.
- Lumen depreciation for LED is often stated as L70 or L80 at a given hour rating; HID uses lamp lumen depreciation curves and group relamping schedules.
- IP rating covers dust and water ingress; BUG covers backlight, uplight, glare; CCT and CRI describe color, not efficacy.
- Surge protection, thermal management, and driver lifetime are critical for roadway reliability. Dimming may use 0–10 V, DALI, or proprietary protocols; photocell receptacles commonly follow ANSI C136.10.
- Luminaire delivered lumens = bare lamp lumens × ballast factor × optical efficiency for HID; for LED, use tested luminaire lumens.
Worked example
A luminaire is rated 15,000 lm initial. Lamp lumen depreciation is 0.90 and luminaire dirt depreciation is 0.95 at the maintenance interval. Maintained lumens = 15,000 × 0.90 × 0.95 = 12,825 lm. If the layout needs 12,000 maintained lm per luminaire, it passes - but only if the 15,000 lm is a luminaire rating, not a bare-lamp rating.
Traps that cost marks
Comparing bare-lamp lumens with luminaire lumens, ignoring ballast factor, treating CCT as a proxy for efficiency, assuming IP65 means vandal-resistant, and forgetting that driver surge ratings and ambient temperature affect warranty and output.