光學測量基本參數

　　問幾乎任何電氣工程師，甚至適度的模擬和電源的專業知識，以評估電源的效率，他或她會知道如何做到這一點，或至少如何開始的過程。你得到一個虛擬負載或（甚至更好）的有源負載，測量電壓和電流到電源，測量相同的參數在電源的輸出，做一些基本的計算，你有初步的答案。如果需要，在一個輸入值和負載范圍內運行測試，以及在靜態和動態情況下。它可能會有點復雜，但基本的設置和過程有這樣做。

　　現在要求同一個工程師測量光源的效率，如LED或CFL，有很多混亂。為什么？因為測量光學參數帶來了一系列新的問題，其中許多問題比基本的電學測量更為復雜和微妙。例如，你想在所有波長的光輸出功率，只有可見光譜，或選定的頻帶（如IR，或在可見光片）？你想要的力量，在所有方向，或只是一個特定的方向和立體角度？

　　Optical measurements have a very long history， going back hundreds of years. Some of the terms and concepts are unchanged over the years， while some have been updated to SI-based units （International System of Units）， so there is occasional confusion as old and new terms are used， or old terms have been formally redefined （what is a “candlepower” unit， anyway？）。

　　Before you can get the right instrumentation and set-up， you have to be familiar with basic optical parameters and terminology of photometry （measurement of visible light） and colorimetry （measurement of colors）， so you can be sure you are measuring what you really need to know. Also keep in mind this critical and basic difference between electrical measurements and optical ones： in most cases （but not all， RF is an exception） when you measure electrical power， you measure voltage and current， and then calculate power via analog circuitry or digital processing. However， when you measure optical power， you really are measuring the power itself via a transducer with output voltage or current which has a well-defined correlation to the impinging optical power.