The Commission for Dark Skies


Home & Commercial 'Security'* Floodlighting

How-to install a 'security' floodlight

Both these steps will make criminals more visible. The UK Government Crime-prevention website states: "The form of lighting currently found many domestic locations is a 250 or 500 watt tungsten halogen floodlight controlled by a movement sensor (passive infra-red, PIR). Increasingly, over-bright and misdirected LED lights cause problems of glare, environmental disruption and skyglow. This is unfortunate, as in many locations it is inappropriately installed and other forms of lighting could make for a better choice.". See also, the advice available from the Institute of Lighting Professionals [pdf version].

Interactive image: Instructions for use

Please hover your mouse cursor over the angles on the left hand side (below) to view the effects of installing a floodlight at various angles

Select angle

The view


Schematic Diagram
with a 72o opening angle
Note: Some floodlights have a much larger spread, as below


At an angle of 90 degrees from the vertical, the light is shining directly outwards, making it impossible for onlookers to see any criminal activity.

At 67o, the problems persist as at 90 degrees, making your 'security' light a serious 'security' risk.

The floodlight has an opening angle of 72 degrees, and so the light needs to be angled at less than half that (i.e. less than 36o) to illuminate the background (in this case, a wall).

At 22o, the floodlight begins to become a 'security' aid. The house wall is illuminated, and so any intruder is highlighted against the background even if (as in this case) the background (i.e. the gate) is dark. However, when standing closeby, the light source is still visible, which impedes the ability of a nearby witness to identify an intruder.

Pointing a floodlight directly downwards is the best solution. The background wall is illuminated, and the bulb of the floodlight is no longer visible, making it easier on the eye. However, the floodlight is still over-powered (in this case, a 500W bulb); such a bulb will always generate strong shadows for people to hide in. The best overall solution is a floodlight pointing directly downwards whilst using a low powered bulb (60-120W will aid onlookers, without generating glare).

The disadvantages of using home "security" floodlights

See also our lighting and crime webpage for more information.

The response of the DIY stores

Since a 500W lamp is 14 times brighter than the Small's lighthouse, and we are all supposed to be saving energy these days, CfDS has been in dialogue with several of the major DIY/household goods retailers, with a view to having them phase out 500W lights and sell more lights (e.g. the Astrica) which shine preferentially downwards and help preserve the stars. Surprisingly, we have had little success. One manufacturer is even selling lamps labelled "sky-friendly", though they manifestly are not!

The only retailer showing any interest has been B & Q. By promoting products, in particular the Astrica range, which have been designed with the specific intention of reducing stray light, B&Q have been a willing partner in supporting the CfDS campaign. Unfortunately however, B&Q and most other DIY stores, continue to sell lighting that is, as the Government states, "...the most inappropriate form of lighting available."

Additional notes

  • * The word 'security' is in quotation marks because there is no conclusive evidence that lighting makes an area more secure. Lit premises as well as darkened ones are broken into, and crimes are routinely committed beneath lights. Lights certainly assists a criminal to see what to do and how to escape, and some 'security' lighting assists the criminal by blinding potential witnesses and cloaking the intruders' activity.
  • The floodlight in the photographs at the top of this page has a 72 degree opening angle, although some floodlights have a much greater spread (the floodlight pictured below has an opening angle of over 100 degrees)
  • All the photographs in the interactive demonstration above, were taken with a digital SLR camera, with auto-exposure. This mimics how the human eye reacts to light levels.
  • At high light levels the pupil of your eye will shrink to prevent damage, reducing the amount of light that hits the retina.
  • Similarly, at high light levels the exposure time of the camera will shrink to prevent damage, reducing the amount of light that hits the camera's detector.
  • The floodlights do have one saving grace; they have a very well defined edge in their light opening angle, as shown in the photographs to the right.