How to light a framed pet portrait at home

This page explains how to light a framed royal pet portrait in a home so that people can see its colours clearly while the print keeps them as long as possible. It covers how light damage adds up, how much light people actually need, which bulbs show reds and golds correctly, why LED lamps suit art, and where to aim a lamp so it does not bounce off the glass into someone's eyes. The advice comes mostly from the Canadian Conservation Institute, which publishes lighting guidance for museums, and it works for a single portrait over a sofa. The main framing and hanging guide covers the frame and the wall.

Light damage is a dose

Every hour of light adds to the damage. The Institute measures the amount of light falling on a surface in lux, and defines the total exposure, or dose, as the light level in lux multiplied by the time in hours. A dim wall for many hours can give a print the same dose as a bright wall for a few hours.

The Institute's fading tests make the scale clear. One day of sunlight gives the same dose as one year of display at 50 lux. Eight months of sunlight equals 400 years at 50 lux. And the Institute says there is no true recovery from faded colours: restoring them means replacing the original material with new material.

Here are the light levels the Institute gives for common situations:

Two ways to lower the dose follow from the definition. You can lower the light level, with a dimmer or a weaker lamp. Or you can shorten the hours, by switching the lamp off when nobody is in the room. Both count equally.

How much light people need to see

The Institute says 50 lux became the museum benchmark because colour science showed it was enough for the eye to work in full colour vision. Research in the 1980s found that a 25-year-old looking at a light-coloured object of moderate detail sees almost as well at 50 lux as in full sunshine.

That changes with the viewer and the picture. The Institute's visibility table allows up to 3 times the light for each of four harder cases: a dark surface, low-contrast details, fine details, and an older viewer. It says a person aged 65 needs several times as much light as a 25-year-old to see as well, even with glasses. The factors multiply, so an older person looking for fine detail in a dark object could need 3 × 3 × 3 × 3 × 50, or 4,050 lux.

For a pet portrait, two of those cases are common. A black labrador, a black cat or a dark background is a dark surface. A grandparent looking at the portrait is an older viewer. So a dark portrait in a room used by older family members may need more light than 50 lux to be seen well, and it pays to choose a lamp that gives good colour at a modest level instead of a bright one.

Which lamp: halogen, fluorescent or LED

The Institute's bulletin on LED lighting compares the lamps directly. A 60 watt traditional incandescent lamp, a 35 watt halogen lamp and a 9 watt LED lamp all give about the same amount of light. The rest of the power is lost as heat and infrared: 58, 33 and 7 watts. The Institute says there is no infrared radiation from LED lamps, so the light beam is "cold". Its guide to temperature adds that incandescent lamps, including halogen, can heat surfaces because of their high infrared content.

The bulletin also compares lamp life. It gives halogen lamps 2,000 to 2,500 hours and white LED lamps 20,000 to 50,000 hours. At 12 hours a day, that is 5.5 to 6.8 months for halogen and 4.6 to 11.4 years for LED. The Institute sums it up: halogens need replacing twice a year, while LED lamps need changing once a decade.

On damage, the bulletin is careful. It says LED lamps that give good or excellent light cause no extra damage to objects. It also reports that some early consumer LED lamps with a strong blue spike faded some dyes up to twice as fast as a museum-grade lamp. The answer is to buy a good LED lamp, and the next section explains how to recognise one. On ultraviolet, the bulletin says the output of the common blue-pump LED lamps falls by a factor of 1,000 between their blue peak and the ultraviolet boundary at 400 nanometres, and keeps falling beyond it.

Colour: CRI, R9 and colour temperature

CRI

The colour rendering index, or CRI, measures how correctly colours look under a lamp compared with ideal white light. The maximum score is 100. The Institute used to recommend a minimum of 85 for fluorescent lamps and now recommends 90 or above for LED lamps. It says the Energy Star 2017 standard, the most widely used standard for general LED lamps in Canada and the United States, asks only for a CRI of 80, which the Institute does not consider adequate for museums and art galleries.

R9, the red score

CRI is an average over eight pale colours. The Institute says an additional saturated red, labelled R9, is the hardest colour for most LED and fluorescent lamps to show well, even when their CRI is high. It defines two grades:

• Good light: CRI of at least 90 and R9 of at least 50.
• Excellent light: CRI of at least 90 and R9 of at least 90.

R9 matters for royal portraits because so many of them are red. In the gallery, the Maharaja golden retriever wears a red jewelled turban, the Patiala Pomeranian sits on a red throne, and the Regal Feline wears a red and gold robe. The Institute describes lamps with an R9 below zero as completely lacking in red output, and such a lamp cannot show a red turban as it was painted. Look for the CRI and R9 figures on the lamp box or the maker's website before you buy.

Colour temperature

Colour temperature describes whether white light looks warm (yellowish) or cool (bluish), measured in kelvin (K). The Institute says it is a matter of preference, and that the old belief that viewers always prefer warm light at museum levels has been shown to be false. Its one recommendation is to use the same colour temperature for all lamps in one space. It adds that 3000 K, the colour of a halogen lamp, is still the target for many makers of good LED lamps, and calls it a pleasant all-purpose choice for anyone who does not want to experiment.

Where to aim the lamp

Glazing acts like a mirror. Florida State University's guide to reflection explains that a smooth surface reflects light at a definite angle, and that light striking a mirror at an angle is reflected at an equal angle. So a lamp that shines at the glass from the same height as your eyes bounces straight back into them.

Use that rule to place the lamp:

1. Put the lamp above the portrait and in front of it. Ceiling track lights, or a wall light fixed above head height, do this. The light hits the glass from above, so its reflection heads downward toward the floor, below the eyes of people standing or sitting.
2. Keep the lamp off to the side of the main seat. If the portrait faces a sofa, a lamp placed to one side sends its reflection to the other side, away from the sofa.
3. Check from where people sit. Sit in the usual chair and look for a bright spot on the glass. If you see one, move the lamp until it disappears.

Glare also comes from the room. The Institute says any bright lamp or window shining in a viewer's eyes reduces what they can see, and suggests louvers or extension tubes (small tubes that fit over a spotlight to narrow its beam) on lamps, and curtains or blinds on windows. It adds that current LED lamps tend to produce more glare than older lamps because of where the LEDs sit in the lamp, so a fitting that hides the bare lamp from view helps. The page on glass or acrylic for a framed print covers coated glass, which cuts reflections that lamp placement cannot.

Avoid lights fixed to the frame

Some frames carry a small lamp fixed to the top edge. The Institute advises against these. Its guide to framing works on paper says not to attach light fixtures to frames, because they produce excessive light levels, create a hot spot on the picture and add to fading. Its guide for paintings says picture lamps attached to frames are rarely successful, give uneven light and can overheat a painting. Light the portrait from a fixture set back from the wall instead.

Dimmers and timers

A dimmer lowers the light level, and a timer or a habit of switching off lowers the hours. Both lower the dose. The Institute says most LED lamps need special dimmers, because dimmers from old lighting systems may not work properly, and that the right dimmer for each lamp is listed on lamp packages and online.

A short checklist

• Choose a wall that direct sun does not reach. The page on safe places to hang a framed print explains why.
• Buy LED lamps with a CRI of 90 or more and an R9 of 50 or more.
• Use one colour temperature for every lamp in the room.
• Light from above and in front, and check for reflections from every seat.
• Turn the lamp off when the room is empty.

The lamp decides how the colours of the portrait look in your room. If you are still choosing a style, the article on how to choose a royal portrait style for your pet helps you pick colours that suit your pet's coat and your room.