Abstract: A novel apparatus and method is disclosed for measuring the reflectance of a colored area of skin in response to green light as a means for assessing the degree of erythema or pigmentation of the area of skin. The apparatus has a mutually screened, green light emitting diode and photosensitive electrical component (typically a cadmium sulphide photoresistor or a silicon photodiode), arranged in a holder and connected to conventional electronic circuitry, so that the amount of light reflected by the area of skin and impinging on the component may be measured and then displayed on a voltmeter allowing a quantitative assessment of erythema or pigmentation. The apparatus has both medical, veterinary and cosmetic applications, for example in assessing the response to treatment of inflammation of the skin, or a safe level of exposure to UV light.