Outdoor lighting

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Lighting types

The available lighting types are covered in Lighting category articles. The types most often used outdoors are filament lamp, linear halogen, CFL and sodium. LEDs are now becoming a realistic option too for city gardens.

  • Low pressure sodium
    • extreme energy efficiency, can put out 10-20x as much light per watt as filament lamps
    • pure yellow light
    • Long 9 minute warmup time so only for photocell/timer use
  • High pressure sodium
    • very high energy efficiency
    • golden orange light
    • slow 2 minute warmup, so only for photocell use.
  • White sodium
    • a variation of HPS. White light, but lamp colours tend not to match each other well. Good where one is used, less so where more are used.
  • HID
    • very high efficiency
    • good white light if you avoid high colour temperature bulbs.
    • lamps can explode at end of life.
  • Linear fluorescent
    • very high efficiency
    • can be fitted under soffits, but not a very warm & homely appearance.
    • Pick an electronic ballast suitable for sub-zero starting, or it might fail to light in a cold winter.
    • Can be used on PIR, tube life suffers quite a bit in hours, but not in days of use.
  • CFL
    • medium to high energy efficiency
    • Light output can be reduced, initial light output low, and warmup time prolonged in subzero weather. Outdoor lamps somewhat resistant to this are available.
    • PIR use reduces bulb life, but the more expensive electrodeless CFLs are immune to this issue.
  • LED
    • medium energy efficiency, but limited power
    • Light quality tends to be cold
    • Many LEDs fade with use
    • Various colours available for parties etc
  • Mercury
    • horribly cold white light
    • medium energy efficiency
    • under a minute warmup time
    • obsolescent
  • Halogen, linear
    • low energy efficiency
    • often far too bright
    • Using them on PIR keeps run costs down
  • Halogen reflector lamps, low voltage
    • can light individual trees, shrubs & other features
    • don't overdo the wattage, 50w is generally excessive outdoors
  • Halogen reflector lamps, mains
    • as above but lamps fail easier & earlier and produce less light.
    • Best avoided.
  • Filament lamp
    • lowest energy efficiency, high run cost if kept on. Best used on a PIR.


Control methods

Switch

Lights get left on by mistake, and the switch is often not where you need it. Wasteful of energy & money, inconvenient, and a trip hazard. Pet paws can be badly injured by being trodden on in the dark.

PIR

PIRs (passive infra-red) detect the movement of warm bodies, and switch off after a short time of no detected movement. These are usually the best option for outdoor lighting, but like anything they have their issues.

PIRs shouldn't stare into the sun, doing so can affect their ability to detect consistently. However sometimes its the one practical option, and they sometimes do work ok like this, sometimes not.

  • detector angle & positioning

The power switching device in a PIR is either a relay or a triac. Triacs are a bit cheaper, but are prone to being killed when a filament lamp blows (especially with halogens). Also triac PIRs can misbehave with CFLs. Relays click when switching, triacs are silent. Relay PIRs are compatible with all current and future lighting types, triacs can only be counted on to work with filament lamp types.

Modern PIRs also detect outdoor light level, and don't come on if its daylight. Check the setting on this, it can come preset way off (adjust it at dusk).

Extending the detecting range of a PIR is unlikely to be possible, due to the way the detector and its lens work. If you need more range, fit a 2nd PIR detector in a suitable place.

PIR detection angle can be reduced to some degree by taping over the sides of the lens, but this affects straight ahead detection performance too.

If a PIR is triggered by pets, pointing the detector up a bit more may stop this.

Timer

As dawn & dusk times varies considerably, timers are wasteful of energy, and the unnecessary on time reduces lamp life in days (not in hours). Timers should be replaced with a photocell when a light needs to be on all night, or with a PIR when the lamp type and application are suitable for that.

Photocell

Switches on when it gets dark, switches off when it gets light. Take care over setting the light level switching points, they're often left set way off. Clean the light detecting cover occasionally.

Photocells run lamps much more of the time than PIRs, a PIR is preferable in most home situations.

Photocells & timer

The 2 can be combined with good results, if for example you want lighting on from dusk to 1 am. Best used with very high efficieny lighting types.

Mini PIR

Mini PIRs with a short detection range are useful where the house is very close to the street. They're the same as a conventional PIR but without the fresnel lens.

Run down timer switch

Press the switch and it stays on for a presettable time. These are sometimes used as stairwell light switches in flats.

Beam break

In situations where a PIR is unworkable, such as a shallow porch that opens onto the pavement, its possible to use a beam break detector. When someone walks into the porch, they break the light or IR beam crossing the entrance, but passers by don't trigger a response. Beam break detectors are now uncommon, having been almost totally displaced by PIRs. You may have to use a security system beam break detector with a separate relay.

IR beam should be used where security matters. Commercial detectors use IR. Visible light beam is easier to set up in some situations, eg when multiple mirrors are used.

Split control

Where more than one light fixture is used, if they cover different areas its often an advantage to control them separately, reducing total energy use.

Multiple control

Large sites can benefit from multiple control methods, eg an 18w sodium lamp on all night providing low level security lighting, and white lighting on a PIR for security and access.

Old options

These are little used now, but have their uses on occasion:

  • Pressure switch mats - standing on the mat switches the light on. Use these mats with a run-on timer
  • Pneumatic: rubber tube operates a pressure switch when driven over. They only detect vehicles in practice, and are easy to defeat. Useful for very long driveways, private roads etc

Matching control system to lamp type

They don't all work properly together.

PIRs: with several lamp types the PIR must have a relay, not a triac. With all lamp types, relay PIRs are more reliable.

Sodium & mercury are slow to warm up, so are only workable with control methods that stay on a long time, and come on well before light is wanted, ie photocells and timers.

Control systems that stay on a long time (photocells, timers, switches) are best used with high efficiency lighting, or tend to end up costly to run.

Low efficiency lighting (filament, halogen) has the highest run cost unless used for short times only. PIR or beam break switches are ideal.

If colour lighting is wanted, CFL, linear fluorescent and LED are available in various colours. Halogen and filament are too, but colouring these lamps is done in a way that massively reduces their energy efficiency, and its poor to begin with.

If you're looking for minimum run cost security lighting on a large site, high pressure sodium is it, with upto 200 lumens per watt.


Common issues

Wattage

Lighting of unsuitable wattage is often seen, especially when linear halogen is used. The prime offender is 500w linear halogens. End users should also be aware that that LEDs & all types of discharge lighting put out several times as much light per watt than filament lamps.

Glare

Its best to avoid lighting up roads, neighbouring properties, adjacent hillsides etc. It annoys people, and wastes light youre paying for, so you need a higher wattage lamp at greater cost to do the job. It can also create an accident risk on roads, and consequent legal liability.

Carriage style light fixtures can have glass panels removed and replaced with sheet ali or mirrored glass to cut down on lost light. No, not all of them :) Mirrored glass needs the back painting to prevent loss of silvering.

PIR dimming fittings

These run a lamp dimly, and swich it to full power when motion is detected. Just one of these can cost you thousands in wasted electricity. See Dimmed PIR Lights for explanation.

Height

High output lights intended to cover a wide area need to be mounted high up. Otherwise they fail to light much of the area, and cause heavy glare. Many linear halogens have been fitted only 8' off the ground, causing intense dazzle and lousy visibility. Access for relamping is also important, mounting a light fitting near an upstairs window can achieve more coverage while still allowing easy relamping. High power lighting really needs more height to get decent coverage. Lighting posts aren't cheap, but they do cut down on the necessary power consumption a lot.

When budget is restricted, trees can sometimes be used to mount lighting. Allowance should to be made for tree growth, and a light type used that won't set fire to leaves & twigs.

Catenary wires also work, but their appearance often isn't liked for domestic use. Such wires should be fairly tight or the light swings about in the wind. Not all walls, posts etc can handle the sideways pull.

Light pollution

Any light that heads upwards is money and energy wasted, and causes problems for astronomers. Many decorative fittings are far from ideal in this respect. High power fittings such as halogens should always be set to eliminate light pollution.

Astronomy facilities can filter out low pressure sodium light pollution, but not other light types.

Placement

Positioning a light fitting above the entrance door has the advantage that it lights up the visitor's face, and doesn't create glare for the person indoors. A light further away can do the exact opposite on both counts.

Relamping

Relamping fixtures mounted high up can be a real issue. This is especially true if you're liable to reach pension age in the current property. If you need a lot of light, a few lights within reach are a lot easier to maintain.

Difficult to reach fittings should definitely use long lived lamp types. Leaving them on all night if not needed is better avoided, it only hastens their demise.

Lamp life:

  • Low pressure sodium
  • High pressure sodium
  • White sodium
  • HID
  • Linear fluorescent 20,000 hours for T8, but much less on a PIR
  • Thinner linear fluorescent aren't suitable for the low temps of outdoor use
  • CFL 3,000-12,000 hours, but much less on a PIR
  • LED widely varying lifetimes, 15,000hr typical, some less, some up to 50,000hr
  • Mercury
  • Halogen, linear 1,500hrs
  • Halogen reflector lamps, low voltage 1,500hrs
  • Halogen reflector lamps, mains 1500hrs, but expect premature failures
  • Filament lamp 1,000hrs
  • Longer life versions of filament & halogen are also available, with upto 4500hr life. They put out less light per watt. The same can be achieved by running a 240v bulb on 220v, using an 18v transformer. see Lamp life

Overlapping areas: if you may be unable to relamp promptly, placing fittings with overlapping lighting areas enables good lighting to be maintained with some dead bulbs.

MICC

MICC cable is unique in that its insulation sucks water vapour out of the air, and its too easy to make end seals that don't remain totally vapour tight long term. Hence this type of cable has an extra failure mode compared to other cable types when used on outdoor lighting. SWA is more reliable.

Water

All fittings should shed rain coming from above, and drain any rain that gets in out of the bottom. Sometimes fittings are seen that don't obey these basics, and they have a habit of eventually filling with water and taking out the power.

Globe breakage

Glass globes can be shattered if the screws retaining them are tightened at all. Its best to leave a very little bit of movement.

Screws on fixtures

Screws rust and jam. Screws in aluminium fixtures corrode the ali as well. Replacing them with wire ties or cable ties avoids this problem.

Fences

Its not good practice to fix cable or lights to wooden fencing. Fences rot & collapse after a while.

Junction boxes

These should be above ground & suitably waterproof. Anything below ground will fill with water at some point.

Feed arrangement

Outdoor lighting is much more prone to failure than indoor. Outdoor lighting should not be fed from the same RCD/MCB as indoor lighting, or failures are often imported to the indoor lighting.

If multiple lights are fed from multiple MCBs/RCDs/rcbos rather than one, a fault only takes out one part of the system, rather than all of it.

Climbing plants & fire

Lamp types vary widely in their ability to set fire to plants. Linear halogens run extremely hot, and plant life must always be kept away from them. Sodiums & LEDs run fairly cool, and can be nestled among foliage.

T&E cable

Regulations have become a good bit more demanding in the 17th edition. Lots of old installs exist using T&E clipped direct, which has 2 issues. There is a theoretical risk of cable degradation, but practically it doesn't seem to be a problem. Also such cable can be cut into by secateurs.

Diagram

Unless its obvious, keep a diagram of your lighting setup, or at least where the cables run. Fault finding years later when the details have been forgotten is much harder.

Low voltage lighting

12v lighting is a lot easier to install for a DIYer that isn't upto speed on wiring regulations.

  • Lamp types are restricted to halogen, LED, 12v CFL and miniature flourescent tube.
  • Max cable length is limited
  • Underwater pond lights are available


See also