| angle between a defined datum axis related to the luminaire and the horizontal when the luminaire is mounted for photometric measurement Note 1 to entry: The defined datum axis can be any feature of the luminaire, but it will usually relate to a feature that is nominally aligned with the horizontal such as an axis through the luminous opening or an axis through an array of LEDs or a fixing spigot entry axis. Note 2 to entry: The tilt during measurement is expressed in radian (rad) or degree (°).
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