We all know that LED light bead is a semiconductor light-emitting device, semiconductor is a heat-sensitive device, that is to say it is very sensitive to temperature. Or that the temperature will directly affect its performance and parameters. As an electric - light conversion device it is the most important indicator is how many watts of electric power input, output how much luminous flux (lumens), we call the luminous efficacy (luminous efficiency), this indicator represents the most important quality indicators of the LED lamp beads. This index represents the most important quality index of LED lamp beads. The user is also according to the luminous flux he needs (lumens) to choose the lowest wattage LED lamp beads.
However, although the LED bead device itself has a luminous efficacy, but it does not mean that the user can directly enjoy the luminous efficacy, because the LED bead device assembled into a lamp will lose part of the luminous efficacy. We first do not consider the light mask transmittance (assumed to be 100%, in fact, usually about 90%), and mainly to consider the light effect of the LED light source itself. This light effect we also divided into cold light effect and hot light effect. Most people may not pay attention to the difference between these two kinds of light effect, so we are here to discuss the cold light effect and hot light effect.
Simply put, the cold luminous efficacy is the luminous efficacy measured when the LED bead light source is at room temperature (25C), while the hot luminous efficacy is the luminous efficacy measured after the LED bead light source is thermally stabilized. Specifically, we usually use an integrating sphere to measure the luminous efficacy of LED light beads, then the luminous efficacy measured immediately after the power is turned on is the cold luminous efficacy (assuming that the room temperature at that time is 25 degrees), and this "immediately" is about 5 seconds or less. The hot luminous efficacy is to wait at least half an hour to three quarters of an hour to reach thermal equilibrium (or thermal stabilization). Nowadays, we usually say that the light effect is cold light effect, or most of the light effect indicators that we usually indicate on the shell or packaging are cold light effect.