The spectral sensitivity and long-term stability play an important role in providing reliable daylight detection. The most critical part of any PECU is the light sensor. Switching level, switching accuracy, and switching ratio. A further 100hrs/year on a typical 100W load results in an additional 10kWh/year consumption. Generally consumption is less than 5W (approx 44kWh/year) and many are less than 0.25W (which equates toīurning hours have the most dramatic effect on consumption. The amount varies according to the technology used. PECUs affect energy consumption in 2 ways: PECU Consumption Typically a 1:0.5 ratio is ideal for this (e.g. This is typically a number of minutes, and the idea of negative ratio units is that the ON level needs to predict when the lamp will achieve suffcient output, whereas the OFF level is when the light is no longer needed. Most street lighting loads have a warm-up time during which the lamp achieves full brightness. When the ON and OFF levels are the same (1:1 ratio) As can be seen from Table 1, below positive ratio units have signifcantly longer annual burning hours than negative ratio units When the ON level is lower than the OFF level (e.g if the load switched ON at 70Lux and switched OFF again at 105Lux, then the unit has a ratio of 1:1.5). The ratio between the two light levels is known as the switching ratio. They switch the supply ON to a load when the light level falls beneath a given value (usually at Dusk), and switch the supply OFF when it rises above another level (usually at Dawn). Introduction to photocells, or Photo-Electric Control Units (PECUs) light operated switches.
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