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  • Wuxi Kinglux Glass Lens Co.Ltd
  • ADD:No.286,Changjiang North Rd,New Dist,Wuxi,JS prov,China
  • Tel: 86-510-66759801
  • Fax: 86-510-84602998
  • Mobile phone: 86-18168862789
  • E-mail: ledglasslens@163.com
  • Contact person: Huimin Zhang
  • LED Primary Optic
    Mar 28, 2018

    When we think of an LED optic, we tend to think of a clear plastic lens that is placed on top of the LED itself to focus or spread the light. If this is your thought process, you’ve gone too far. xp-lLets take a step back and look at the LED itself. See that small protective dome over the diode? That is actually called the primary optic which serves to protect and shape the output of the small diode. The light from the LEDs primary optic is still too broad for most applications, lacking intensity over distance. This is why most LED fixtures use secondary optics (lenses, reflectors, TIR optics, etc.) to collect all that light and magnify its intensity towards the target.

    Creating lenses and reflectors for LEDs (solid-state lighting) is much different than just scalingUntitled Banner (1)them down from other light sources. This might seem like a logical way of creating them, as LEDs have much smaller form factors than other light sources, but they also differ in how they emit the light. As you can see from incandescent bulbs, they illuminate in 360 degrees, but LEDs are directional lighting, illuminating only 180 degrees. This is attributed to the design of an LED, as you can see to the left, a light emitting diode consists of one or more die, mounted on a heat-conducting material, with the primary optic enclosing the die. Therefore, the maximum angle LEDs can emit is 180 degrees as the substrate is on the back side of the die.LED break down

    The Primary Optic

    Typical spatial distribution is what manufacturers use to describe the light coming from an LEDs primary optic. This basically means the shape or spread of the light from the center of the diode. As we talked about earlier, LEDs face in one direction, so imagine a line running straight down from the center. Spatial distribution is measured in degrees from this center point.

    Let’s take the Cree XP-G2 for example, which is rated at 115 degrees, meaning the beam will extend 57.5 degrees on either side. Just because it is rated for this, does not mean you get the entire lumen output of the LED across the whole spectrum. The light will be stronger the closer you are to the center, like other point of light sources. Take a look at the ‘Typical Spatial Distribution’ graph of the XP-G2, a graph like this will be on the emitters data sheets, which can be found on all LED product pages on the site.Spatial Distribution Cree XP-G2 LED

    Along the center axis, the LED emits 100% of its relative luminous intensity and will lose intensity the farther away you move from the center. Say we are running a Cool White Cree XP-G2 at 350mA, we know from the data sheets that at this drive current, the LED will give off 139 Lumens, it’s rated output, at the central axis. At 30 degrees from center, the output of the LED drops to 125 Lumens. Going down the distribution curve at 40 degrees, the output reaches only 111 Lumens. This continues to drop until at 57.5 degrees you are only getting about half the lumen output at 70. It is obvious when you are losing this much light output over the spectrum, that a secondary lens or optic is needed to intensify that light and use the brightness and efficiency of LEDs to their full capacity.