Fundamentals of UV and light protection

Ultraviolet (UV) rays, UV-A 380 to 315 nm, UV-B 315 to 280 nm – Visible light (VIS) 380 to 780 nm – Infrared rays (IR) IR-A 780 to 1.400 nm, IR-B 1.400 to 3.000 nm, IR-C 3.000 to 1.000.000 nm
Ultraviolet (UV) rays, UV-A 380 to 315 nm, UV-B 315 to 280 nm – Visible light (VIS) 380 to 780 nm – Infrared rays (IR) IR-A 780 to 1.400 nm, IR-B 1.400 to 3.000 nm, IR-C 3.000 to 1.000.000 nm

Sunlight – damaging radiation

The radiation spectrum which reaches us from the sun provides to us, as we know, not merely visible light, but also the radiation invisible to us.

The radiation which reaches the earth with sunlight can, if we are overexposed to it, cause conditions such as a sunburn or heatstroke.

Yet this radiation also jeopardises historical materials and preservation materials. Since 1967, UV radiation has increased by approx. 15% for the position of the sun in February (BayFORKLIM Final Report 2000).

Historic paint stains fade, historic binding agents are destroyed by the UV radiation and chalk off; due to UV rays, paint layers become brittle and IR rays create tension which makes the coats of paint partially burst and fall off; preservation materials become yellow, etc.

To comprehend these processes, it is helpful to take a look at solar radiation:

 

Aus Norden kommt doch keine Sonne - also auch keine UV-Strahlung?

Diese Annahme ist leider gründlich falsch!

Die Begründung findet man z.B. in Rudolf W. Schulze, Strahlenklima der Erde auf Seite 90:

"Das besondere Merkmal der Ultraviolettenstrahlung gegenüber der Globalstrahlung ist ihre hohe Streuung an den Molekülen der Atmosphäre, die nach kürzeren Wellenlängen nach dem Rayleighschen Gesetz umgekehrt zu deren vierten Potenz ansteigt.

Dies hat zur Folge, daß die aus dem Himmelsgewölbe zum Erdboden kommende Ultraviolettenstrahlung meist 10- bis 20-mal stärker ist als die direkte ultraviolette Sonnenstrahlung."

Sie sehen, auch auf der Nordseite eines Gebäudes kommt man um einen UV-Schutz nicht herum wenn es gilt wertvolles Kulturgut zu schützen.

Gleichwohl stellt sich die Frage wieso dann in der Praxis viele Schäden an Kunstgegenstände in Südausrichtung zu finden sind.

Nun, neben der UV-Strahlung, welche die molekularen Struktur der Materialien schädigt, spielt die IR-Strahlung, je nach Aufbau der Kunstgegenstände eine entscheidende Rolle.
Die mit der IR-Strahlung einhergehende Erwärmung und Abkühlung der Objekte setzt diese einer ständigen Ausdehnung und Kontraktion aus. Durch diese Längenänderungen kann es zu Spannungen im Material kommen, so dass, die durch die UV-Strahlung in seiner Molekülstruktur vorgeschädigten Materialien entsprechende Risse zeigen.

Sie sehen, sind die Objekte entsprechend empfindlich bedarf es sowohl UV++ als auch IR-Schutz.

  

The degree of damage depends on the wavelength of the radiation

Now, one could claim that is does not matter in terms of the degree of damage whether materials are irradiated with electromagnetic radiation (i.e. light with 546 nm or UV radiation with 389 nm).

However, this is not the case!

In a paper by Judd and Hilvert, an analysis at 546 nm determined a relative damage factor of 1 based on the extent of the damage (i.e. the measured colour changes, brittleness etc.); however, at i.e. 389 nm, a relative damage factor of 90 – and at 365 nm, even 135! (see image)

That means that ideally, an object irradiated with i.e. 389 nm ages 90 times faster than one irradiated with 546 nm!

 

When short-wave radiation hits an object, part of it is absorbed by this object and re-emitted as longer-wave radiation (warmth); some can lead to damage in the molecular structure.
When short-wave radiation hits an object, part of it is absorbed by this object and re-emitted as longer-wave radiation (warmth); some can lead to damage in the molecular structure.
By way of absorption, the molecular structure of the material can be damaged. This also applied to many other UV-protection materials, yet not to ours (see 'Effects and Possibilities of our UV Protection').
By way of absorption, the molecular structure of the material can be damaged. This also applied to many other UV-protection materials, yet not to ours (see 'Effects and Possibilities of our UV Protection').

Not all materials react equally

According to their particular molecular structure, different materials react differently.

Here, you will find an exemplary compilation of materials with properties which can be critical in photochemical terms / Limit wavelength of the spectral transmission edge (1%), considering the colour reproduction at a rate of Ra 98%

  • 385 nm plastics with inherent UV protection (for interior application)
  • 385 nm destruction of modern binding agents (interior application)
  • 385 nm wood components, untreated
  • 385 nm organic stains in modern paint media (interior application)
  • 385nm paper (basis: rags)
  • 395 nm historic binding agents
  • 395 nm historic textiles with pre-existing damage
  • 400 nm organic stains in historic paint media
  • 400 nm stains in untreated wood
  • 400 nm historic watercolours and inks
  • 405 nm plastics without inherent UV protection
  • 405 nm stains in historic textiles
  • 405 nm protein structures (i.e. moist and dry preparations, leather, feathers, skin, hair)
  • 405 nm stains in protein structures

50 Lux – a rating with little informative value

The gauging sensor of the light intensity gauges (luxmeters) was developed to attain values adapted to the brightness sensitivity displayed by humans.

The gauging sensor of a luxmeter was NOT developed to gauge absolute energy quantities!

For this purpose, there are spectrometers which – depending on the wavelength – can detect the corresponding energy quantity.

This aforesaid positioning of a luxmeter results in the display by the luxmeter of i.e. a certain quantity of energy at 550 nm (green light) with i.e. 50 Lux, while in the blue range of the spectrum, however - at i.e. 405 nm – an approx. 100-fold higher energy quantity hits the object, whereby the value of 50 Lux is also displayed here!

 

Do you remember the analysis performed by Judd and Hilvert?

At 405 nm, the relative damage factor according to Judd and Hilvert amounts to 60! Of course, at the same amount of energy as for 546 nm!

From this, one can conclude that if the luxmeter would display 50 lux (for a light source reflecting primarily in the blue range)...

...in fact, however, a 6,000-fold higher damage factor would apply!
(100-fold higher energy amount [to attain 50 lux] x 60-fold relative damage factor)

Perhaps you would agree with us that one should change the heading of this paragraph (in light of this correlation) to ""50 Lux – a misleading value""...

...at least when the 50-lux value is viewed in an isolated context.

An interesting observation in this context, too, is also that there are simple luxmeters on the market which only measure starting at 470 nm – that is to say, between 400 nm and 470 nm, this measurement structure would leave a disastrous measurement gap! After all, most of the simple UV gauges have a capacity which extends to 400 nm. In this context, the energy quantities in these UV gauges are only viewed in an integrative context and likewise weighted – mostly in such a manner that as a rule, they weight the energy less between 380 nm and 400 nm.

 

Aber wir haben doch eine Farbverglasung - die muß doch UV-Strahlen abhalten?

Aber wir haben doch eine Farbverglasung - die muß doch UV-Strahlen abhalten?

Auch diese Annahme stimmt nur zum Teil!

Man muß sich schon die Transmissionskurven der einzelnen Farbgläser im Detail ansehen!

Dabei muß man auch unterscheiden ob es sich um durchgefärbte Gläser oder Gläser mit einem Farbauftrag handelt.

Hier haben wir Ihnen einmal verschiedene Beispiele zusammengestellt.
 

The entire area marked in yellow (displaying harmful radiation) can, as a rule, pass through the so-called UV-protection panes with 99% protection – ask to see the gauged values.
The entire area marked in yellow (displaying harmful radiation) can, as a rule, pass through the so-called UV-protection panes with 99% protection – ask to see the gauged values.

The matter of 99% UV protection - or a statistic

Essentially everywhere, one can read about 99% UV protection...

... yet just as the 50-lux value, this 99% value should be critically scrutinised!

After all, this value does not correlate to the specification of an exact wavelength, but instead only relates to the physically-defined UV range.

That is to say, if there is a range of between approx. 310 nm (here, as a rule, lies the starting point for the transmission of most of the panes used in architecture) and 380 nm, 1% energy penetrates the so-called ""UV-protection glass"", a 99% protection applies.

As a rule (see measurement curves) for a laminated safety glass pane with 1.52 mm untreated PVB film at 380 nm, one arrives at 1% transmission; for a laminated-safety glass pane with 0.38 mm PVB film, the 1% transmission edge lies at approx. 365 nm.

At 400 nm (according to the analysis by Judd and Hilvert, here, a relative degree of damage amounting to > 60 already applies!), the transmission for laminated safety glass panes with 1.52 mm of untreated PVB film and ""99% UV protection"" already once again lies at approx. 65%; that is to say, the relative degree of damage is reduced to approx. 39.

For laminated safety glass panes with 0.38 mm of untreated PVB film and ""99% UV protection"" even once again at approx. 90%; that is to say, the relative degree of damage is reduced to merely approx. 54.

In our standard UV protection panes, the 1% transmission edge lies at 400 nm. With that, we reduce the relative degree of damage at 400 nm to approx. 0.6!

In addition to our standard UV protection panes with 1% transmission at 400 nm, for custom panes, also 1% transmission edges at 410 nm, 420 nm or 430 nm are possible.

In this context, please always scrutinise the specification of percentage values, and when in doubt, ask to see a measurement curve. In addition, you will find an interesting article on this topic athere.

What's more, particularly when applied as transparent UV protection, many protective materials disintegrate over time, since the UV protection is attained by a ""sacrificial structure"". However, this does not apply to our UV protection.

You can find out how our UV protection workshere.

 

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