我在手机上装了个免费的照度计（ light meter)，可以很方便得测出光照度。今天阴天下雨，在南面窗台上是1000多勒克斯，离开窗台一米就只有几个勒克斯了，所以蝴蝶兰君子兰想要开花还是要尽量靠近窗台为好。
勒克斯lux，法定符号lx,是照度(Illuminance)的单位。被光均匀照射的物体，在1平方米面积上所得的光通量是1流明时，它的照度是1勒克斯。适宜于阅读和缝纫等的照度约为500勒克斯。
还有另几种非SI的光度学单位：
发光强度 烛光(candlepower) = 1 坎德拉照度
英尺烛光(Foot-candle)，字面意义是发光强度为1坎德拉的点光源的1英尺距离处的表面的照度。1ft-c = 1 lm/ft2 = 10.764 lux. 工业上常常采用1ft-c = 10 lux.
下表是英尺烛光和勒克斯的换算表：
各种兰花需要的英尺烛光值：
To grow and bloomproperly : Low end High end
• Low light orchidsneed 1,000 fc 1,500 fc
• Moderate lightorchids need 1,500 fc 3,000 fc
• High light orchidsneed 3,000 fc 4,500 fc.
美洲兜兰、文心兰、石斛等，需要养在光线明亮但是没有阳光直射的地方，适合放在朝东的阳台，给多的光照，但是要避免暴晒或直射。
喜欢中等光照的就包括蝴蝶兰和兜兰，它们喜欢放在朝东或朝西的窗台，要避免阳光直射。
Low light, Warm growing orchids enjoy a north or an east, protected west or shaded south windows of the home. Standard householdtemperatures are adequate. Orchids that are classified as low light, warmgrowing are: Paphiopedilum or Lady Slipper（拖鞋兰）, Phalaenopsis（蝴蝶兰） and Oncidium（文心兰）
Moderate to highlight, Warm growing orchids. These orchids like a lot of light and warm household temperatures. They thrive in a west or south window. From early May to late September, you should watch light levels in south windows to avoid burning; youmay have to move your orchid away from the window or place them behind a sheercurtain to decrease light intensity. These orchids like to dry betweenwatering. Orchids that are classified as moderate to high ligh are: Cattleya（卡特兰）, Dendrobium（石斛兰）, and Vanda（万代兰）.
Moderate to highlight, Warm growing orchids. These orchids like a lot of light and warm household temperatures. They thrive in a west or south window. From early May to late September, you should watch light levels in south windows to avoid burning; youmay have to move your orchid away from the window or place them behind a sheercurtain to decrease light intensity. These orchids like to dry betweenwatering. Orchids that are classified as moderate to high ligh are: Cattleya（卡特兰）, Dendrobium（石斛兰）, and Vanda（万代兰）.