LED Glare

LED Glare - Learning Objectives

1. What is glare?
2. Why is glare a bigger problem than ever before?
3. How many types of glare are there?
4. How to minimize glare?​

Since LED light sources do not mimic daylight, there is a need to have some metrics for comparison to familiar light sources of sunlight, incandescent and halogen. Lighting Facts is a good start, for more details consider the Kelvin, CRI, and TM-30 metrics.

Good lighting design should always include analysis of color rendering, light intensity, beam spread, flicker, and glare.

Too bright!

GLARE = Visual Disability Due to the extremely small light source of LEDs, glare can cause visual disability - squinting and averting the eyes.

The angle of incidence = the angle of reflection.

If you think about glare like a game of billiards, the way to win is to understand that 'the angle of incidence = the angle of reflection'. 
If you see a reflection of the light source in your computer, tv, or art, move the light or move the reflective surface. 

The two photos show the same creek. In one image you can see the rocks below the surface, in the other the reflection of the sun on the surface prevent you from seeing what is beyond. This example shows how important it is to calculate the angle of your light source and the reflections it will create.

Direct Glare can cause temporary blindness.

Have you ever made the mistake of looking directly into a flashlight? You cannot seen anything immediately after exposure to that bright light the filled your field of vision.  This is a example of direct glare, where you are temporarily blinded by a too bright light.
Whenever your eyes see a terribly bright light, you squint, if you don't squint fast enough, you are temporarily blinded. Aging Eyes are even more debilitated by the blinding effects of direct glare.
No one wants to look at the sun. With LED lights becoming so bright, and because they are a 'point source' they are especially risky when it comes to direct glare.
Your peripheral vision is also vulnerable to direct glare.

How to avoid Direct Glare?

Several solutions reduce the risk of direct glare; shielding and diffusing.
SHIELDING - hiding the light source behind a fixture, or 'regressing' the light source far inside a fixture such as a downlight or streetlight will reduce the opportunity for direct glare.
DIFFUSING - softening the harshness of a LED light with a diffuser specifically designed to reduce the surface brightness of the LED while distributing the light over a wider area is a useful technique; however, with LEDs being overly bright, diffusing alone may not be enough to mitigate the extreme point source brightness and may also require shielding.

Related Topics

Manufacturer's Educational Links, LED for your B&B, Color in Paint - Why they Fade

Footnotes

1. Professor David Heeger - Light/Dark Adaptation
2. www.lightingfacts.com
3. IES RP-28-16 Seniors and Low Vision http://www.ies.org/
   

Photo Credits

• Lighting Facts Card - DOE - Department of Energy
• Test Colors for CRI & Light Source Color Rendering Chart - EYE Lighting
  
• TM-30 Test Colors - IES TM-30-15 Errata

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