Street Lighting: A Metric for Specifying White Light

该项目将调查附属(住宅)街道的照明。近几十年来，这主要是使用低压钠(LPS)和高压钠(HPS)灯来提供的。这些灯具有很高的发光效率(光输出)和较长的工作寿命，这些特性被认为足以超过它们较差的颜色特性/橙色外观和较差的显色性。照明行人环境时，亮度是一个重要的考虑因素，因为它与人们的安全感有关/更明亮的街道被认为更安全。街道照明工程师建议，使用更白的光源，如金属卤化物(MH)和紧凑型荧光灯(CFL)，可以创造更清晰和更明亮的环境，此外，使用这些更白的光源的街道照明可以采用较低的照度(照度)，同时保持相同的亮度和清晰度。这种照度的降低将抵消MH和CFL灯的功效，后者往往低于HPS和LPS灯，甚至可能导致能源消耗的减少。这一轶事证据已经被申请人进行的一系列实验所支持(EPSRC授权参考。GR/25074/01)显示节省了约30%的资本和能源成本。这种灯类型和照度之间相互作用的一个主要原因是，人眼在夜间发现的低水平光下的反应不同于在白天典型的较高水平下的反应，但照度规范仅根据白天的反应进行校准。BSI道路照明委员会(CPL/34/8)在2003年修订的BS5489-1中考虑了白光效应。本文件根据犯罪率和交通流量对BS EN 13201-2：2003中规定的S系列附属街道照明等级进行了解读。BS5489-1：2003识别白色照明的指标是通用显色指数(CRI)，这是因为它提供了白色灯与标准HPS和LPS灯之间的明显区别。因此，当使用具有CRI&GT；60的灯时，BS5489-1：2003允许降低S系列的一个等级，即降低照度。不幸的是，根据定义和实践，CRI不能可靠地用来预测任何东西，也许除了颜色外观的自然度。这在夜间会加剧，因为CRI是基于白天光照水平下的视觉反应。即使在白天，CRI也无法预测不同类型灯下环境的视觉外观，例如LED灯下的颜色外观也不能很好地预测。虽然CRI规范可能适用于现在普遍用于路灯的灯，但有时它会给出不适当的指导，例如在推断以区分一些其他类型的灯时。需要更好的规范方法来避免误用。同样重要的是，需要提供研究证据，这些证据可以转化为指导意见，便于执业照明工程师获取。否则，它可能会被忽视，浪费改善视觉环境和能源消耗的机会。该项目将进行进一步的测试，以补充最近研究的证据，以生成一个数据集，以测试用于预测降低照度是否合适的工具。这些测试包括亮度匹配和视力，使用的灯范围更广。将利用与照明工程师的咨询来确定应该如何呈现调查结果，以确保在准确性和易用性之间取得适当的平衡。

This project will investigate lighting in subsidiary (residential) streets. In recent decades this has been provided mainly using low pressure sodium (LPS) and high pressure sodium (HPS) lamps. These lamps have high luminous efficacy (light output) and a long working life, and these characteristics were considered sufficient to outweigh their poor colour properties / the orange appearance and poor colour rendering. Brightness is an important consideration when lighting pedestrian environments because it is linked to the perception of safety / brighter streets are considered to be safer. Street lighting engineers suggested that using whiter light sources, such as metal halide (MH) and compact fluorescent (CFL) lamps, would create a clearer and brighter environment, and furthermore that street lighting using these whiter light sources could adopt a reduced illuminance (light level) whilst maintaining the same level of brightness and clarity. This illuminance reduction would offset the efficacy of MH and CFL lamps, which tends to be lower than HPS and LPS lamps, and may even lead to a reduction in energy consumption. This anecdotal evidence has been supported through a series of experiments carried out by the applicant (EPSRC grant ref. GR/25074/01) demonstrating savings of approximately 30% in capital and energy costs. A primary reason for this interaction between lamp type and illuminance is that the human eye responds differently at the low levels of light found at night-time than it does in the higher levels typical of daytime, but illuminance specification is calibrated only to the daytime response. The BSI road lighting committee (CPL/34/8) took account of the white light effect in the 2003 revision of BS5489-1. This document interprets the S-series of lighting classes for subsidiary streets specified in BS EN 13201-2:2003 according to the rates of crime and traffic flow. The metric by which BS5489-1:2003 identifies whiter lighting is the General Colour Rendering Index (CRI) and this is because it provides an obvious distinction between the white lamps and the standard HPS and LPS lamps. Thus, BS5489-1:2003 permits a reduction of one class of the S-series, a reduced illuminance, when using lamps having CRI >60. Unfortunately, CRI, by definition and in practice, cannot reliably be used to predict anything except perhaps the naturalness of colour appearance. This is exacerbated at night-time because CRI is based on the visual response under daytime light levels. Even at daytime levels CRI fails to predict the visual appearance of an environment under different types of lamp, and colour appearance under LED lamps, for example, is not well predicted. Although the CRI specification may work with lamps now commonly used for street lighting there will be occasions when it gives inappropriate guidance, for example when extrapolated to distinguish between some other types of lamp.A better method of specification is needed to avoid misapplication. Of equal importance is the need to provide research evidence that can be translated into guidance that is readily accessible to practising lighting engineers. Otherwise it may be ignored, wasting the opportunity for improvements in the visual environment and energy consumption.This project will carry out further tests, supplementing the evidence from recent studies, to generate a dataset against which to test tools for predicting whether an illuminance reduction is appropriate. These tests include brightness matching and visual acuity, using an extended range of lamps. Consultations with lighting engineers will be used to determine how the findings should be presented to ensure an appropriate balance between accuracy and ease of application.