¹ - The term 'efficiency' is actually fairly meaningless. Lamp Type Power Luminous Efficacy (lm/W) Efficiency ¹ The figures here are representative only, and in some cases significant variations may be seen, depending on the source of the information. However, it does not refer to the quality of light emitted from the various sources listed. This allows more-or-less direct comparisons between different light sources, as shown in the following abridged table. The lumen output gives the total luminous flux of a light source by multiplying the intensity (in candela) by the angular span over which the light is emitted.Įspecially since LED lighting has become popular, it's common to refer to the luminous efficacy of lamps in lumens per watt (lm/W). Up until fairly recently it was mainly used by lighting professionals, but the introduction of 'high efficiency' lighting has pushed the term into more common usage. The term 'lumens' (abbreviation lm) refers to the total light output from a source. Night vision is exclusively the regime of the rods, but it is possible to have red light for illumination and it won't cause a loss of night vision because the rods don't respond to red light. Rods are around 100 times more sensitive than cones. Our eye-brain combination tells us that we are seeing in shades of grey, even though the rods respond most strongly to light within the blue-green range (centred on and around 498nm). This is based on rods alone being activated, so there is no colour differentiation. Colour vision is impaired in the mesopic region, so colours appear muted.įinally, at very low light levels, we have scotopic vision. The rods are more sensitive than the cones, but only respond to light intensity on the grey scale, and they do not react to colours. At lower light levels, we are in the mesopic region, and vision is from a combination of cones and rods. We have full colour vision in this range because the colour receptors in our eyes, the cones, (red, green and blue) are all activated. Photopic vision is the way we see when the area is well lit (daylight for example), with an luminance levels of more than 3cd/m2. See the table below for some examples of light levels.įigure 1 - Vision And Receptor Regimes (Osram Sylvania, 2000) It also takes up to 5 minutes for our eyes to adapt to bright light from darkness. It takes time (20-30 minutes, age dependent) for our eyes to adapt to low light levels after being subjected to bright light. The human eye has a huge range of light sensitivity, from starlight (about 1E-6 cd/m²) up to somewhat greater than direct sunlight (1E6 cd/m²), although at any particular time the range is less (around 1,000:1). Luminous emittance is also known as 'luminous exitance'. Luminous emittance is the luminous flux per unit area emitted by an illuminated surface. Illuminance refers to the light that falls on a surface per unit area. Luminance ( L) is a measure of how bright a light source appears, and is typically measured in candelas per square metre (cd/m²). In addition, we may also refer to luminance and/or illuminance. Candelas and Lumens describe the light emitted from a source, and Lux describes the light level at a given distance from the light source - typically at a work or road surface, etc. Which one is used depends on how the measurement was taken, and whether it describes the light output or the amount of light available at the 'destination'. There are basically three different ways to describe how much light a given light source provides.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |