The Lux two-minute explainer: IP ratings

Everyone knows about IP Ratings. We throw around IP44s and IP65s with abandon, confident that we know all there is to know about these things. Then, one day, someone asks us what they actually mean . . . and we discover that there is some important, and surprising, information tucked away in the small print.

 

Let’s open the box on see what’s going on behind the numbers.

As we know, the basic meaning behind the IP Rating system is to provide a guide to the degree of protection that a luminaire has against the ingress of solids and liquids.

 

The First Number (IPn…) relates to solids and ranges from 0 – 6. 

The ratings offer a logical progression from larger to smaller objects, so the lowest number (zero) indicates that there is no protection against touching live parts within the equipment.

The actual sizes on which the tests are based may be arbitrary, but it all makes sense as a way of going about things.

The most common rating for a light fitting intended for general interior use is IP20, which tells you that nothing larger than 12.5mm diameter can reach a live part when the equipment is fully assembled.

The idea that the rating is based on a complete piece of equipment is an important one. There are many electrical fixtures that use a protective cover to conceal the live parts. The IP rating only holds good with that cover in place.

 

The Second Number IP...n) relates to liquids and ranges from 0 – 9. 

A luminaire being tested for IPx6 at a manufacturer's laboratory

Unlike the natural progression assigned to the ingress of solids, the second number relates to styles of liquid ingress; drips, sprays, splashes, jets and immersion. 
Note this: protection against one type of ingress must not assume protection against other types of liquid ingress. This is a common misunderstanding with IP liquid ratings.

There is general consensus that light fixtures divide into two categories; those that offer some protection against water ingress and those that don’t. The first group generally come under the IP20 rating mentioned above, but those fixtures that are intended to come into contact with water will be rated between IP44 to IP68, depending on the severity of the contact.

Surprisingly, a lot of street lighting is rated at IP44 although it might be assumed that such exposure would call for a higher rating because of the location of the equipment. However, street lighting lanterns are unlikely to be exposed to the type of water attack that the other tests apply, so IP44 is appropriate for their task. There is also a commercial aspect to this; if a luminaire requires a higher rating then it will demand a higher price to cover the additional engineering.

But it is with the higher ratings where care needs to be taken, as all may not be as it seems. The IP ratings come with caveats and protection against specific site conditions cannot be assumed. The actual protection that is provided should be explained in the manufacturer’s documentation.

What may also not be clear is that the ratings may refer to the luminaire in a given situation. An IP65 downlight may be appropriate for installing into the ceiling of a shower cubicle, but it doesn’t necessarily mean that the IP rating is good in, say, an exterior canopy. Lighting for a ‘shower cubicle’ fixture often assumes that the luminaire is installed in a solid ceiling, where water can only attack the luminaire from below. That may not be the case in an exterior canopy.

Some manufacturers provide the additional information that tells you the IP rating at the back of the fixture. It’s not common, but not unknown, and is certainly worth confirming with the manufacturer if you’re looking for under-canopy lighting.

A Komee floodlight on test 

The conditions required with immersible ratings must also be checked with care. The shorthand for an IP67 luminaire is that it can be immersed up to a shallow depth of only 1000mm. But the manufacturer’s data may put a time limit on that immersion, so an IP67 feature uplight fitted permanently in a garden pond may or may not be fit for purpose.

The gold standard of IP68 also needs to be examined, because a similar situation may also prevail there. Not all IP68 luminaires are designed for complete protection against water ingress. An IP68 rating can be given for a luminaire where water can enter but only in such a way that it does no harm.

 

What about other IP numbers

The most common Additional Number in the lighting industry is the one that covers Mechanical Impact Resistance. It’s most commonly seen in relation to exterior public area lighting where there is a higher likelihood of damage being done and equipment being left dangerously exposed. This used to be known as the ‘third’ IP number but this has been superceded by an IK number, and there are 10 ratings available.

The problem with the IK rating is that it’s not easy to imagine what a 500g object dropped from a height of 200mm actually means. As a guide, many manufacturers have their outdoor equipment rated at IK08 and it’s useful to take that as a minimum specification rating.

 

Things that experience has taught us about IP ratings

X does not mean NO

There are also instances where a number is replaced by an X (IP nX or IP Xn). This does not mean that the fixture has no protection against solid or liquid ingress. It means that no data is available for a rating to be provided. 

In the case of solids ingress, a common-sense judgement call could be made depending on the ingress of liquids rating. It’s safe to assume that a housing that doesn’t permit water ingress at IPX4, the lowest number that tests liquid in all directions, would also provide protection against ingress of solids. This remains an assumption, however, and should be declared in any specifications documentation. And, of course, this assumption does not work the other way round. No such assumptions can be made for liquid ingress on the basis of solids ingress ratings.

 

An IP rating is not a cover-all

Just because a product has an IP rating does not mean that it can be used in every environment. A fixture rated at IP65 may have a plastic body that may not be suitable for long-term exposure to sunlight. Similarly, an aluminium or steel housing may not be appropriate to a marine environment. This goes beyond the remit of the IP ratings and requires an understanding of the environment into which the equipment is to be installed. A conversation with manufacturers as to the suitability of their equipment is highly recommended. Be sure to get the information in writing as it could affect guarantees if fittings then fail due to environmental conditions.

 

IP ratings can’t be swapped around

The IP liquids ratings are not cumulative in the way that the solids rating are. An IP66 rating is not ‘inferior’ to an IP68 rating, it’s a different test procedure. Using an IP68 fixture in an IP66 environment can cause a lot of problems. The IP68 rating is based on immersion in water, so any heat generated within the housing is dissipated by the surrounding water. That fixture operating in open air can over-heat and fail as a consequence.

 

Lab tests are not the real world

IP ratings are based on tests carried out in laboratory conditions, in specific conditions, as described in the tables below. In the field, conditions over time will expose any shortcomings and even fixtures with higher grade ratings may still leak over time. This is where it’s important to trust the manufacturer. Do they have history and credibility in the area of usage that you’re concerned with? Trustworthy manufacturers will carry out long-term testing on their products and will also be examining materials and finishes for degradation (paint finishes and plastics are a particular long-term concern)

 

Damage prevention is something else altogether

If the intention is to stop the light from a light fixture, the most effective tool for the vandal is a can of black spray paint. There is no ‘vandal resistance’ rating in the IK system. None of the tests relate to a hooligan with a brick, baseball bat,  airgun or aerosol spray. This is a different standard and another subject.

 

The most usual IP numbers to see associated with luminaires

IP20: for most general purpose interior luminaires
IP44: common for street lighting and basic bollards and floodlights.
IP65: very common for outdoor lighting in public areas and for professional floodlighting
IP67: considered as a luminaire that can be immersed in water, but beware the time-limit caveat on this one.
IP68: an absolute requirement for underwater luminaires, but ONLY underwater.

 

And here are the IP numbers

Protection rating against ingress of solids (IPn…)
0: No protection against contact and ingress of objects at all
1: Protection against objects  >50mm, but no protection against deliberate contact with a body part
2: Protection against objects >12.5mm, such as fingers or similar objects
3: Protection against objects >2.5mm, typically tools and thick wire
4: Protection against objects >1mm, which includes most wires and slender fixings (screws, etc)
5: Protection again ‘dust’, though not entirely prevented, is not sufficient to interfere with satisfactory operation  of the equipment
6: ‘Dust Tight’, meaning that there is NO ingress of dust and provides complete protection against contact with internal parts

Protection rating against ingress of liquid (IP…n)
0: No protection against liquid ingress
1: Protection against vertically falling dripping water.
       Duration: 10 minutes (water equivalent to 1mm of rainfall per minute)
2: Protection against dripping water when the equipment is tilted at 15deg. from its normal position.
    Duration: 10 minutes (water equivalent to 3mm of rainfall per minute)
3: Protection against a spray of water at any angle up to 60deg. from the vertical.
    Duration: 5 minutes. Water volume: 0.7L/min. Pressure: 50-150kPa
4: Protection against water splashing against the equipment from any direction.
    Duration: 5 minutes. Water volume: 10L/min. Pressure: 50-150kPa
5: Protection against water projected from a nozzle from any direction.
    Duration: (at least) 3 minutes. Water volume: 12.5L/min. Pressure: 30kPa at 3m.
6: Protection against a powerful jet of water from a 12.5mm nozzle from any direction.
    Duration: (at least) 3 minutes. Water volume: 100L/min. Pressure: 100kPa at 3m.
7: Protection against a harmful quantity of water when the equipment is immersed, under defined conditions of pressure and time.
    Duration: 30 minutes. With the lowest point of the equipment 1000mm below the surface of the water, or the highest point being 150mm below the surface, whichever is deeper. 
8: Protection against continuous immersion in water beyond a depth of 1m, under conditions specified by the manufacturer.
    Duration: continuous. Depth specified by the manufacturer, generally up to 3m

The IK numbers relating to mechanical impact resilience
00: Unprotected, or where no test has been carried out.
01: Impact energy of 0.15J (Joules), equivalent to dropping a 200g object from a height of 75mm onto the equipment.
02: Impact energy of 0.2J, equivalent to a 200g object dropped from a height of 100mm. 
03: Impact energy of 0.35J, equivalent to a 200g object dropped from a height of 175mm.
04: Impact energy of 0.5J, equivalent to a 200g object dropped from a height of 250mm.
05: Impact energy of 0.7J, equivalent to a 200g object dropped from a height of 3350mm.
06: Impact energy of 1J, equivalent to a 500g object dropped from a height of 200mm.
07: Impact energy of 2J, equivalent to a 500g object dropped from a height of 400mm.
08: Impact energy of 5J, equivalent to a 1.7kg object dropped from a height of 200mm.
09: Impact energy of 10J, equivalent to a 5kg object dropped from a height of 200mm.
10: Impact energy of 20J, equivalent to a 5kg object dropped from a height of 400mm.