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Light Spill and Light Glare are related but they are not the same. We are often asked to quantify Light Spill (Lux) and Light Glare (UGR) by running a computer model. And explaining results in a Light Spill and Light Glare Report.
Lighting glare takes in to account not only the "power" of the light emitting the glare. But also the back ground ambient light level. It is there for a measure of contrasting lighting levels.
Example: A single candle in a dark room, will have a glare. This is because it the flame is very bright compared to the background (ambient) light level. . . . Now imagine that same candle, in a room where the lights are turned on. It would have very low glare as the background light level is much higher, and the contrast in lighting intensity is much less.
Spill is created when a light fitting spills lights all over the place.
Example 1: A candle. A candle produces a lot of spill, the light is not focused at all.
Example 2: A laser. A laser does not create any spill at all, as all of the light is focus in one place. . . . we don't often use lasers in lighting design though. Although some customers do request it. :-) Apologies for below picture, this is to prove this page was written by a human being, rather then AI.
In most quantitative assessments we right there is a threshold. For Lighting Spill & Lighting Glare there are two thresholds we tycpially follow, although councils do suggest different ones sometimes.
Need a Light Spill & Light Glare Report? Please hit big yellow button at top of page, to send us an email.
"UGR, at its most fundamental definition, is a calculation-based metric recommending best practices for minimizing discomfort glare experienced by humans indoors. It is based on the British glare index system where:
UGR and all other systems can be traced back to initial studies in the 1950s. One study in particular, carried out by Petherbridge and Hopkinson, attempted to quantify levels of discomfort glare in human subjects by exposing them to background light paired with glare sources."
Reference: White Paper on Unified Glare Rating (UGR) - NEMA - 2021
Over the last 10 years LEDs (Light Emitting Diodes) have become one of the most predominant sources of light across the world. The "emitters" can give off a very intense light, and as such are prone to producing glare.
For example back in the 90's the bench mark torch for power, was the 6 Cell Maglite, with an Incandescent Bulb. This torch gives out approx. 178 Lumens.
Fast forward 2024, and a small upgrade of the same torch with an LED emitter array and it will produce 3500 lumens.
The intensity of lighting for a given area has increased 20 fold over the last 10 years, and as such the potential for glare has also increased.
The requirements for Lighting Spill & Lighting Glare Assessment pops up from time to time over the UK.
For example we have recently seen below Response from Royal Borough Kensington and Chelsea
In the absence of sufficient light mitigation measures and a lighting strategy, the proposals would result in an unacceptable impact from light glare and light spill on local residential amenity including neighbouring properties. Therefore, the proposals are not acceptable and are contrary to policies CD9 and GB10 of the Local Plan 2024. Note
So in the case of Royal Borough Kensington and Chelsea policy GB10 reads as follows:
“Development must not create an unacceptable impact from light glare and light spill on local residential amenity including neighbouring properties and communal gardens, biodiversity, highway and waterway users.”