Advantages: Low cost for initial purchase.

Disadvantages: Inefficiency, low output of light for energy level, and therefore banned for domestic use.

Effect on light sensitive patients: Generally safe although very light sensitive individuals may need to avoid high wattage bulbs.

Advantages: Efficiency. They last about twice as long as regular incandescent bulbs and give off 95% of their initial light output at the end of their lives, and slightly more energy efficient.

Disadvantages: They are on average 5 to 10 times as expensive as their non-halogen counterparts. They are also due to be banned for domestic use.

Effects on light sensitive patients: Many report a severe adverse reaction to halogen bulbs, as they emit more UV and blue light than their Tungsten counterparts.

Advantages: Cheaper to run.

Disadvantages: More expensive to install. More difficult (and toxic) to dispose of. Also due to be banned as they are so much less efficient than LEDs (and they contain Mercury).

Effects on light sensitive patients: Because fluorescent lighting involves the emission of UV radiation it is unsafe for light sensitive individuals (unless covered by protective film or of the ‘double envelope’ type) and for many, unless the ballast is at least 5m from the sufferer. Research by German scientists at Berlin’s Alab Laboratory indicates that compact fluorescent lamps released several cancer-causing chemicals (April 2011).

Advantages: Sodium Vapour lamps are ten times more efficient than incandescent bulbs, in fact these are the most efficient bulbs made and one of the cheapest HID bulbs to purchase.

Disadvantages: Yellow tone of light, and still less efficient than LEDs, so being phased out.

Effect on light sensitive patients: This spectral range has no adverse effect and can safely be used for floodlighting and lighting of public places.

Advantages: Very economical, with the most long-lasting bulbs.

Disadvantages: Cool and bright white LEDs can be blinding, and cause migraines and skin rashes. A study (Environmental Science and Technology, January 2011) has found that LEDs contain lead, arsenic and a dozen other potentially hazardous substances.

Effects on light sensitive patients: They emit almost no UV, far less even than an incandescent bulb, which is a good point. However, the popular ‘cool white’ and ‘bright white’ emit large amounts of (near UV) short-wavelength blue which for many is as dangerous as UV. The warm white can be tolerated my many, especially with a shade/diffuser. The ‘heritage’ range (normally only in lower powered bulbs), although expensive to buy, should be safe for most people. They emit a yellowy light like the very old-fashioned incandescent bulbs. The filament-style bulbs are usually the safest. BUT: Some very sensitive people cannot tolerate any LEDs, maybe because of features other than the light emissions.