Another type of device used is the light tube, also called a tubular daylighting device (TDD), which is placed into a roof and admits light to a focused area of the interior. These somewhat resemble recessed ceiling light fixtures. They do not allow as much heat transfer as skylights because they have less surface area.
aNOtHer type Of deViCE uSeD Is the light tubE, alSo calLed a TubULaR dAylightinG dEViCe (Tdd), wHich is pLacEd intO a Roof And aDmITS ligHT To A FOCuSed area oF THE interior. These somEwHAt reSeMBLe receSsed cEiliNg lIght fixturES. THeY do not aLlow aS mUch Heat tranSFer as SKYLigHTS bECAuSE they havE lesS SurFace Area.