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LED light quality not determined by the specs on the box

LED light quality not determined by the specs on the box

I recently read an article in MIT Technology Review (How to Choose an LED Light Bulb) that provides ways to distinguish between the good and not-so-good LED light bulbs on the market. One point of reference was the quality of light emitted.  Since light quality is extremely important to us at Leapfrog (it’s our main focus in our LED lamps), I was especially interested in how buyers are advised to assess the quality of light.

 Three specification values were specifically cited:

  • Number of lumens – The higher the lumens the brighter the light.
  • Color temperature (or CCT) – The lower the CCT the more yellow the light. The higher the CCT the more white the light. 2700K – 3000K is the norm for most indoor lighting. Note: For a CCT light appearance scale, see our FAQ under What is CCT?
  • Color quality, known as CRI – The measure of a light source’s ability to render color accurately compared to that of the sun. A perfect CRI would be 100, meaning the light source renders color the same as the sun; however, good color rendering is achieved with a CRI of at least 85.

Lumens, CCT, and CRI are undeniably valid metrics in measuring light quality. With recent LED performance improvements, a good ranking of these metrics is getting much easier to achieve than previously. As long the metrics are understood, a simple glance at the box or lamp datasheet will provide all three specifications. However, they paint an incomplete picture when isolated from other information.

LED light quality incomplete picture

What else plays a role in the quality of light? While there are many, many parts that affect light quality, here are three that we pay a whole lot of attention to:

  • Optics: Lens design is extremely important in providing a glare-free, evenly distributed, soft-edged light. This is generally attempted through light diffusion or reflection techniques, though all manufacturers use different designs to try to reach this effect. Good results are hard to achieve. For a more in-depth analysis, see Light Quality of LED lamps. Ask your lighting representative about glare, light distribution, and especially for down lighting, the spot light “edge”. If your lighting representative is unsure, speak directly to the manufacturer.
  • Components: Not only should all components be of top quality, but the manufacturer needs to independently validate the specifications provided by the supplier for any given component and ensure cohesion between components provided by different suppliers. Ask your lighting representative how the manufacturer tracks the supply chain and tests the components. Again, speak directly to the manufacturer if your lighting representative is unsure.
  • Composition (materials): As far as the optical components are concerned, Poly-Methyl-MethAcrylate, or PMMA, is the most common material used to produce a good optical surface finish (it’s also called Perspex or Plexiglas).  That said, where the PMMA comes from and the level of impurities matter, as the loss figure ranges from 0.1dB/com to 0.7dB/com—the difference between 5% and 50% loss for some optics designs. Ask your lighting representative or manufacturer whether the PMMA is “optical grade”.

While optics, components, and composition are not available on the box or packaging, they have a big impact on the quality of light and should be factored into any purchase decision. As a matter of fact, even assembly can affect light quality (the better the optical efficiency, the more sensitive it is to correct placement).  So be sure to look beyond the specifications—as they alone do not tell the whole story.


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5 Responses to LED light quality not determined by the specs on the box

  1. Interesting and illuminating, but the discussion arose out of consumer concerns and the relevance of “40w equivalent” type ratings.

    Realistically, I don’t think consumers will sign up to a classification that offers three parameters, let alone six.

    I think they’d rather continue to be confused by the current system. Which is a shame, as it is unhelpful and unreliable as a buying metric.

  2. Another concern that even your company’s specifications do not address is the light output stability. I’ve been very disappointed to find that many LED lamps flicker severely at line frequency. I happen to perceive this directly, but it is also a concern for anyone using video equipment around the lamps. Please encourage your engineers to include specifications for depth and frequency of any output “ripple” from your lamps.

  3. Hi Loren – In response to your comment about the stability of light output (flicker): you raise a very good point. At Leapfrog Lighting, we look at flicker performance as part of our product assessment.

    Flicker is usually due to the switching frequency or other characteristics of the power supply – such as a thermal fuse flicking in and out or due to certain dimmers that are in the lighting circuit. Energy Star requires that LED lamps have flicker above 120Hz (i.e. higher than 120 flickers per second), but there are lots of anecdotal stories about people being affected by 120Hz flicker from fluorescent tubes, so a higher flicker frequency is desirable. All LED lamps will have some degree of flicker, this can not be avoided. The trick is to make sure that any such flicker is at a high enough frequency that it is not visible to humans. Leapfrog Lighting’s lamps have flicker that is well into the kHz range (i.e. thousands of flickers per second, as opposed to hundreds per second). No way a human will ever see it.

  4. I have 4 LED bulbs in my home now. I love them. I bought them before incandescent bulbs were discontinued. I am slowly replacing all my florescent bulbs which is the only type of lighting I have in my home. I bought them before all the information was made available. I like natural daylight lighting, do you have any suggestions. I do want to say I have no flickering and my newest one is about 6 months old.

    • @Hilah, if you like natural daylight lighting, you would look for an LED lamp with a color temperature between 5000K and 6500K. You can find a color temperature guide near the bottom of this page:
      As for flickering, a variety of things should be examined before purchasing. Incompatible dimmers are a big cause of flickering. If you plan on dimming, check with the manufacturer whether the LED light bulb is dimmable AND whether your dimmer is compatible. Other things can cause flickering as well, such as the load on the system.

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