Photochromic ShieldSafety Analysis

by Steve Reed

IntroductionPhotochromic safety shields have tremendous consumer appeal based on their outstanding convenience and safety benefits. Although the technology is advanced, the function is simple. A photochromic shield automatically “shifts” between tint in daylight and clear at night. It is the UV from sunlight which activates the photochromatic tint, therefore car head lamps and streetlights have no effect and the shield remains clear at night. The motorcyclist who rides in varying lighting conditions ranging from bright sunlight to darkness of night benefits most from a photochromic shield because of its ability to automatically shift between clear and dark tint, thereby eliminating the need to switch shields and carry extra shields.

However, one decades old ophthalmic lens concern is sometimes correlated with photochromic shields. What happens when a driver wearing photochromic corrective glasses enters a dark tunnel during sunny conditions? Could this present a danger due to inadequate light transmittance through tinted photochromic glasses which do not instantly shift to clear? This sounds reasonable, however out of the millions of photochromic ophthalmic users there are no known lawsuits associated with this assertion. So in practical terms this has been a non-issue. Furthermore, since motorcycle helmet shields are not ophthalmic devices, the original argument does not even apply. Therefore, even though entering a tunnel with a photochromic shield is not a safety issue, various shield configurations are thoroughly analyzed nonetheless with regard to entering tunnels.

Based on real-world conditions and the riding habits of a typical motorcyclist, the following comparative analysis concludes that a photochromic shield is the safest overall option because it combines the best safety features into one shield thereby eliminating almost all dangers found with other types of safety shields, and it is more safe than a clear shield when entering a tunnel. The analysis below provides details supporting this conclusion.

Product liability is an important consideration with any safety product. Adequate product labeling and sufficient warnings are essential. Inclusion of educational product literature regarding photochromic characteristics and care instructions is highly recommended.

Diamond OptixSuwanee, GA

USA

Steve Reed(770) 833-0320

steve@diamondoptix.com

AnalysisSunglasses - Worst Safety Score

Unfortunately this is probably the most common practice among motorcyclists. Even though it’s uncomfortable, wearing Sunglasses inside a helmet to bypass the inconvenience of switching between clear and tinted shields and carrying an extra shield at all times in preparation for day and night conditions, proves how inconvenient switching shields is. This common practice creates two potentially serious dangers:

Wearing sunglasses subjects the motorcyclist to possible serious injury to eyes and face in the event of an impact.

When entering dark tunnels, quick removal of sunglasses from the line of sight is typically impossible. Restoring proper vision would require taking a hand off the handlebars, lifting the shield, removing the sunglasses, and then holding the sunglasses while continuing to operate the motorcycle (all with gloves on). Riders do not attempt this maneuver for obvious reasons; it is dangerous and very difficult. Therefore, a rider wearing sunglasses entering a dark tunnel can experience limited vision during an extended period of time with no remedy.

Wearing sunglasses inside a helmet is therefore dangerous.

*See Addendum A for an un-edited first hand account from a motorcyclist describing the serious consequences he experienced while riding and wearing sunglasses inside a helmet.

“Drop-Down” Inner ShieldsThis configuration combines two shields in an attempt to make both clear and tinted shields available for varying light conditions. A clear shield is fitted to the helmet in a conventional position, and a secondary tinted “inner shield” rotates up and down from within a pocket located in the helmet’s shell above the rider’s forehead. A mechanism controlled by the rider physically moves the inner shield back and forth.

The clear shield is safe for use at night (with the tinted inner shield moved out of view) and the tinted inner shield can be relocated in front of the rider’s viewing area during daylight.

When entering a tunnel the tinted drop-down shield can be manually moved out of the line of sight relatively quickly with minimal effort, and the outer clear shield remains in place. The tinted inner shield is then repositioned again when exiting the tunnel. The ability to move the tinted inner shield in and out of view is advantageous, however there are unfortunately a number of disadvantages and safety concerns associated with this configuration.

Inner shields leaks light from around the edges to varying degrees and cannot conform to every face, especially the nose area. The inner shield and its exposed edges are in close proximity to the face and eyes which in an impact could cause serious damage to face and eyes.

Helmets with drop-down shields are inherently larger and heavier due to the shell’s design requiring extra space to house the drop-down shield and associated internal mechanisms which can break and typically cannot be fixed since the actuator resides within the helmet’s shell.

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Heavier weight causes additional neck and shoulder fatigue plus more force and torque on the neck during an impact. Increased wind noise is also common.

Therefore drop-down shield configurations result in larger size, heavier weight, possible internal mechanism breakage, and increased potential dangers to eyes and face. Additionally, this design is not conducive to prescription eyewear due to the close proximity of the inner shield to the eyes.

Aside from the fact they are unappealing from a fashion standpoint, there are multiple dangers and disadvantages associated with drop-down shields.

Clear ShieldClear shields are preferred in night conditions. Its major drawback is during daylight as it offers no tinting ability, which can lead to impaired vision and eye strain from bright light and glare. Unfortunately use of sunglasses is common, presenting serious potential dangers to eyes and face in an impact.

Although the human eye adjusts relatively quickly to variances in light conditions, it cannot adjust instantaneously when transitioning from brightly lit surroundings into a dark tunnel. Nor can anything be done to accelerate this adjustment period. The result is a short period of blindness typically lasting 2 - 4 seconds. Therefore, use of a clear shield when entering a dark tunnel from brightness is dangerous because vision is severely impacted for a period of time with no remedy. At night entering a tunnel is not an issue.

Tinted ShieldTinted shields are preferred during daytime but are not suitable for night use. It is not uncommon for a rider wearing a tinted shield during the day to get caught in diminishing sunlight or darkness without a clear shield to switch with the tinted shield.

The most obvious contradiction to the photochromic “tunnel scenario” is the common use of standard tinted shields which have no shifting capability. The tinted shield has been commonly used for decades, yet there is no perceived safety issue when entering a tunnel. When needed, a tinted shield is raised enough to restore suitable vision immediately upon entering a dark tunnel, and the elapsed time for vision adjustment is minimal. Raising the shield exposes the face to the elements, and therefore caution should always be taken with this action. However this technique is commonly used and accepted, and is the exact same technique which is used with a photochromic shield.

Use of a tinted shield at night is dangerous at all times.

Photochromic Shield - Best Safety ScoreDiamond Optix™ photochromic technology effectively turns one shield into two, automatically shifting from tint in sunlight to clear at night with varying degrees of tint in between.

A Diamond Optix™ photochromic shield is safe for night use because in the absence of sunlight it is clear. But its unique ability to automatically adjust tint level according to the strength of sunlight is what differentiates it from standard shields during day use. Additionally a

photochromic shield eliminates the danger of inadvertently getting caught at night riding with a tinted shield and the need to carry extra shields. No need to stop and switch shields, possibly near traffic.

Prescription glasses can be worn in conjunction with photochromic shields. However, wearing contacts when possible is recommended due to the same safety-related concerns as wearing sunglasses inside a helmet as described above.

When entering a dark tunnel with a photochromic shield in the tinted state, the shield is used in the same manner a standard tinted shield. The shield can be raised if needed (even with gloves on), allowing the eyes to adjust quickly to the sudden change in light conditions. This will expose the face to the elements, and caution should be applied such as lowering speed and allowing extra vehicle distance. This is the same method used with tinted shields for decades. A photochromic shield is clear at night and therefore entering a tunnel at night is not an issue.

Photochromic shield users also benefit from less haze than is found in some tinted shields dependant upon factors such as pigment and polycarbonate quality as well as injection molding process parameters. Therefore compared to some tinted shields enhanced clarity is of benefit.

Photochromic shields by Diamond Optix block over 99% of harmful UV rays.

Addendum AFirst-hand account of the dangers of wearing sunglasses inside a helmet

The following is an un-edited account of events from motorcyclist Scott Otoole.

4-22-07

The bike was a CBRF4i. Nice. It was totaled. I was on city streets going not more then 25 on a bright sunny day. A Ford F150 hit me side on. He was turning left in front of a car that was waiting in traffic in front of me. I drove beside the car to get on the freeway, 880 south. Upon colliding he continued into a parking lot maybe another 25 feet.

I was wearing a full face helmet with sunglasses under a clear visor. Kevlar jacket and gloves. I was told by my plastic surgeon, after recovery, that because of the sunglasses, I had a blown left orbital. I had 6 hours of plastic surgery to fix this and now have metal there. Good thing is the surgeon was excellent and no one can tell. The surgery was all done through lifting skin away from my eye with no cutting.

Other things. I was in a coma for 11 days. I had a badly broken left leg, more pins, and was paralyzed [for a time] from the brain injury. Loss of some short term memory. Will never remember the accident as it happened too fast.

Fully recovered in about 7 months and went back to work. Better than the original speculation that I may not be able to take care of myself again.

-ScottOtoole

Safety Features Clear Tinted Drop-Down

Sun-glasses

Photo- chromic

UV protection • • • • •tinted in sunlight • • • •clear in darkness • • •adequate space between shield and face

• • •shield edges are not exposed to face • • •unobstructed peripheral vision • • •tint covers full viewing area • •discourages use of sunglasses • • •no additional weight to helmet • • • •no internal mechanism • • • •accommodates prescription glasses • • •can move out of vision path quickly • • • •clear shield will never need to be raised while entering a dark tunnel during daylight

• •

Totals 10 11 6 4 12

Addendum BWhich is safest?

Safety Ranking: score 12 Photochromic Best 11 Tinted 10 Clear 6 Drop-down 4 Sunglasses / Clear shield combo Worst

Diamond Optix - All rights reserved v1.5 updated 3-25-2015