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Quick Reference

Essential LED terminology explained in plain language.

A19

The most common household light bulb shape in North America. The 'A' stands for 'Arbitrary' (the standard pear shape), and '19' indicates the diameter in eighths of an inch (19/8 = 2.375 inches). When someone says 'light bulb,' they're almost always picturing an A19. Most A19 LEDs use an E26 base and are available from 40W-equivalent (450 lm) to 100W-equivalent (1,600 lm).

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Beam Angle

The angle between the two directions where light intensity drops to 50% of its peak value. A narrow beam angle (15–25°) creates focused spotlight effects ideal for accent lighting and artwork. A wide beam angle (60–90°+) spreads light broadly, suitable for general room illumination. PAR and BR bulbs are specifically designed to control beam angle, while A19 bulbs emit light in nearly all directions (~270°).

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BR (Bulged Reflector)

A bulb shape with a bulged (rounded) reflector, commonly used in recessed ceiling downlights. BR30 (3.75” diameter) is the most common residential size, fitting standard 6-inch recessed cans. BR40 (5” diameter) fits 6–8 inch cans. Unlike PAR bulbs, BR bulbs have a softer, more diffuse beam edge, making them better for general room lighting rather than accent or task lighting.

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CCT (Correlated Color Temperature)

The numerical measurement of a light source's color appearance, expressed in Kelvin (K). CCT describes where a light falls on the warm-to-cool spectrum by comparing it to the color of a heated black body radiator at a specific temperature. CCT and 'color temperature' are used interchangeably in consumer lighting. Common CCT values: 2700K (warm white), 3000K (soft white), 4000K (cool white), 5000K (daylight).

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Color Temperature

The perceived warmth or coolness of white light, measured in Kelvin (K). Lower values (2200–3000K) appear warm and yellowish, resembling incandescent or candlelight. Higher values (4000–6500K) appear cool and bluish, resembling daylight. Color temperature profoundly affects mood, perception, and even circadian rhythm. Most residential lighting uses 2700–3000K; offices and workspaces typically use 3500–5000K.

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Cool White

A color temperature range of approximately 3500–4500K, producing a neutral to slightly blue-tinted white light. Cool white is often preferred for kitchens, bathrooms, garages, and commercial spaces where a clean, alert atmosphere is desired. It provides good visual clarity and contrast but can feel clinical in living spaces designed for relaxation.

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