LV: Lighting

Lighting

The goal of lightning is to provide adequate lighting in the appropriate places without any glare

• General lighting - there should be an even distribution of light with extra for hazardous areas. Ceilings and walls should be light coloured and non-reflective. Patients should face away from the window in daylight to avoid glare
• Local lighting - take into account inverse square law and also cosine law (put paper as close to 90 degrees to light source as possible to get maximum illuminance
• NB 60yr old needs 3 times the illumination of a 20 yr old due to senile miosis, media opacities and loss of neurons

Glare

• Discomfort Glare - subjective visual discomfort - px feels visually uncomfortable or fatigued. VA not affected by glare and discomfort relieved by tints. EG In uveitis, ocular albinism, cone-rod dystrophy, RP. Can be measured by getting patient to adjust light to a certain level of unpleasantness. No clinical relevance tho
• Disability Glare - Loss of retinal image contrast as a result of intraocular light scatter or stray light. This reduces visual performance. The degree of glare depends on the angle between the task and the glare source & the relative luminance
• Media opacs lead to IO light scatter and veiling luminance across retinal image and a reduction in contrast. Eg ageing, cataract, pos. chamber IOL, PCO, Keratoconus, Corneal Oedema, RK, vit opac

Disability glare can be measured objectively - px viewing an acuity/low contrast chart under controlled lighting conditions. This allows for simulation of everyday situations like flu overhead lighting, sunlight on cloudy day etc. Optom measures VA while shining penlight into pxs eye at a fixed distance and angle (eg 10cm and 30 degrees). Drop in VA of 2 lines or more indicates a significant degree of glare.

Reducing Disability Glare

• Environmental control, task lighting, avoidance of shiny surfaces, tints to reduce retinal illuminance, visors and hats
• People who may benefit from tint - media opac, albino, RP, Cone dystrophies, aniridia (though cone dystrophy may be better), corneal dystrophies, diabetics, uveitis
• Prescribe tints wrt subjective comfort or objective w/low contrast charts vs high contrast charts, varying illumination.

CIBSE Recommended levels for normally sighted px
(in lux)

• Living Room 50, Sewing/Sustained Reading 300, Kitchen 300, Hall/Stairs 150, Bathroom 50, Bedroom 50.
• 50-100% increase in those figures if you're over 65
• 5 times to 10 times increase if you're a VIP. Usually compromise w/1000 lux, adjustable

Bulbz

• Fluorescent is best. Gives poor colour rendering because usually at discreet wavelength but this is irrelevant in a low vision context.
• Discharge tube can be folded to give more compact bulb
• 9w or 11w, high efficacy
• Stays cool even after prolonged application
• NB Px can use any light source and it will not affect the way they read